Basic of Pumps

Fundamental principlesof pump technology

Pump Basics

2005Subject to technical modifications. In appliance of our General Terms of Delivery and Service (see www.wilo.com)

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C O N T E N T

Subject to modifications 03/2005 WILO AG Wilo Pump Basics 03/2005

C O N T E N T

Fundamental principles of pump technology 5

History of pump technology 7

Water supply 7

Wastewater disposal 8

Heating technology 9

Pumping systems 12

Open water pumping system 12

Closed heating system 13

Water – our means of transport 15

Specific heat storage capacity 15

Volume increase and decrease 16

Boiling characteristics of water 17

Expansion of the heating water and protection against excess pressure 18

Pressure 19

Cavitation 19

Design of centrifugal pumps 21

Self-priming and non-self-priming pumps 21

Function of centrifugal pumps 22

Impellers 22

Efficiency 23

Power consumption of centrifugal pumps 24

Glandless pumps 25

Glanded pumps 27

High-pressure centrifugal pumps 29

Curves 31

Pump curve 31

System curve 32

Duty point 33

Adjusting the pump to the heat demand 35

Weather fluctuations 35

Pump speed selection 36

Infinitely variable speed control 36

Control modes 37

Rough pump design for standard heating systems 41

Pump flow rate 41

Pump delivery head 41

Application example 42

Effects of the rough pump design 43

Pump planning software 43

Hydraulics from start to finish 45

Adjusting electronically controlled circulating pumps 45

Connecting multiple pumps 46

Conclusions 50

Did you know... 51

History of pump technology 51

Water – our means of transport 52

Design features 53

Curves 54

Adjusting the pump to the heat demand 55

Rough pump design 56

Connecting multiple pumps 57

Legal units of measure, partial listing for centrifugal pumps 58

Informational materials 59

Imprint 63

Wilo Pump Basics 03/2005 5

In the field of building technology, pumps have avery important role. They are used for a variety offunctions. The most familiar of these is theheating circulating pump. Therefore, it will be thefocus of our discussions on the following pages.

In addition, pumps are used in the fields of watersupply and wastewater disposal:• In pressure booster stations, which are used

whenever the city water pressure is not suffi-cient for supplying a building;

• Drinking water circulation pumps, which ensurethat hot water is always available at each tap;

• Wastewater lifting pumps, which are requiredwhen wastewater or sewage comes from belowthe backflow level;

• Pumps in fountains or aquariums;• Pumps for fire-fighting applications;• Pumps for cold and cooling water;• Rainwater utilisation systems for toilet

flushing, for washing machines, cleaning andirrigation;

• Many other applications.

It is important to remember in this regard thatdifferent media have different viscosity levels(such as raw sewage or water-glycol mixtures).Certain standards and guidelines specific to eachcountry must be followed, which may requirespecial pumps and technologies to be selected(such as explosion protection, German DrinkingWater Ordinance).

Fundamental principles of pump technologyPumps are a vital element of life and comfort for all human beings. Pumps move the fluid whether it is hot or cold, dirty or clean. They do it in a way that is extremely efficient and conserves the environment.

The objective of this brochure is to providefoundational knowledge of pump technology topersons who are currently in vocational or pro-fessional training or retraining. Using simple,explanatory sentences, drawings, and examples,it is intended to provide a sufficient base ofknowledge for real-world use. This should makethe proper selection and use of pumps a matterof everyday routine.

In the chapter entitled Did you know... you can,for each section, test your own comprehensionof the material by answering a series of multiple-choice questions.

As an additional option for gaining more in-depth knowledge based on these “Pump Basics,”we also present our selection of informationalmaterials. It includes resources for self-study aswell as the field-experience-oriented, hands-ontraining seminars we offer.

Refer to the chapter on“Informational materials,”page 59

An ingenious improvement on this concept wasdevised in 1724 by Jacob Leupold (1674-1727),who built bent pipes into a wheel. Turning thewheel forced the water to be lifted to the middleaxis of the wheel. The flow of water in a river alsoserves as the drive of this lifting plant. A particu-larly noteworthy feature of this design is theshape of the bent pipes. It is remarkably similarto the shape of today's centrifugal pumps.


History of pump technology

Water Supply

When thinking of pumps and their history, onemight recall that since the earliest times, peoplehave sought technical means of lifting fluids–particularly water–to a higher level. This wasused both to irrigate fields and to fill the moatsthat surrounded fortified cities and castles.

The simplest scooping tool is the humanhand–and two hands are better than one!

Thus, our prehistoric ancestors quickly had theidea of making clay vessels into scoops. This wasthe first step towards the invention of thebucket. Multiple buckets were then suspendedfrom a chain or wheel. People or animals usedtheir energy to set this water scoop in motion andlift water. Archaeological digs have found bucketconveyors of this kind in both Egypt and Chinafrom around 1000 BC. The following illustration isa reconstruction of a Chinese scoop wheel. Thisis a wheel with attached clay pots, which pourout the water when they reach the top.

Here, too, the operating behaviour is remarkablysimilar to today's centrifugal pumps. The pumpcurve–which, of course, was an unknown conceptat the time–shows the same relationshipbetween the delivery head and the flow rate.Information gathered from various historicalsources has revealed that these screw pumpswere operated at inclines between 37° and 45°.They produced delivery heads of between 2 m and6 m and maximum flow rates of about 10 m3/h.

Refer to the chapter on“Impellers,” page 22

Worm

Drivingfeature

Water is lifted

Illustration of a Chinese scoop wheel

Illustration of Archimedes' screw

Illustration of Jacob Leupold's water wheel

Archimedes (287-212 BC), the greatest mathe-matician and scientist of ancient times,described the screw that would later be namedafter him in 250 BC. It lifted water by turning aspiral/worm in a pipe. However, some of thewater always flowed back, as effective sealingwas then unknown. As a result, a relationshipwas observed between the incline of the screwand the flow rate. A choice could be made inoperation between a greater quantity or agreater delivery head. The steeper the incline ofthe screw, the higher the delivery head when thequantity decreases.

Direction of flow

Illustration of a hypocaust heating system from Roman times

8 Subject to modifications 03/2005 WILO AG Wilo Pump Basics 03/2005 9

H I S T O R Y O F P U M P T E C H N O L O G YH I S T O R Y O F P U M P T E C H N O L O G Y

Wastewater disposal

Although water supply has always been the mostbasic necessity for human life, it was onlylater–almost too late, in fact–that effectivewastewater disposal came into existence.

Wherever settlements, towns and cities formed,excrement, filth and sewage polluted streets,paths and other open areas.

Aside from the horrible smell, this also causeddiseases and epidemics. Bodies of water werepolluted and the groundwater became undrink-able.

The first sewers were built between 3000 and2000 B C. Under the Palace of Minos at Knossos(Crete), brick-lined channels and terra cottapipes have been discovered that served to col-lect and drain rainwater, bath water and sewage.The Romans built sewers in and underneath thestreets–the largest and most famous being thecity's Cloaca Maxima, parts of which are remark-ably well preserved to this day. From here, waterwas fed to the river Tiber (the city of Cologne,Germany also has some underground tunnels youcan walk through that were sewers in Romantimes).

Since no further progress was made in the thou-sands of years that followed, untreated sewagewas still being fed into streams, rivers, lakes andseas as late as the nineteenth century. Industri-alisation and the growth of cities made effectivewastewater disposal essential.

The first centralised sewer and wastewatertreatment system in Germany was created inHamburg in 1856.As late as the 90s, many household sewagesystems in Germany still consisted of septic pitsand drainage pits. Only later did legal decisionsand regional requirements require these to beconnected to the public sewer system.

Today, the drains of almost all houses areconnected directly to the public sewer system.Where this is impossible, lifting plants or pres-sure drainage systems are used.

Industrial and household wastewater is fedthrough far-reaching sewer systems, retentionponds, treatment plants and clarification ponds,and biologically or chemically cleaned in theprocess. After treatment, the water is returnedto natural circulation.

Heating technology

Hypocaust heating systems Relics of what are called hypocaust heatingsystems from Roman times have been found inGermany. These are an early form of floor heat-ing. The smoke and hot air from an open firewere channelled through special chambersunderneath the floors, thus heating the floors.The gases then escaped to the outside throughwall flues.

In the centuries to follow, particularly in castlesand fortresses, the chimneys, which likewisecovered open fires, were not built in a strictlyvertical direction. Instead, the hot fumes werechannelled past living quarters–one of the firstforms of central heating. Another invention wasa system separation using walled stone cham-bers in the cellar. The fire heated fresh air, whichcould then be guided directly into the commonrooms.

Steam heating system Steam heating systems were a by-product of thesteam engine, which came into widespread usein the second half of the eighteenth century. Theleftover steam, which did not condense in thesteam engine, was guided into offices and livingspaces by heat exchangers. One thought was touse the residual energy of a steam heatingsystem to drive a turbine.

Gravitational heating systemwith boiler, expansion tankand radiator

Outer wall

Wall heating flue

Inner wallFloor

Supporting columnsof the floor

CombustionchamberHeating cellar

Disposal channelfor ashes

The most varied pumps and pump systems areused in wastewater disposal. Here are just a fewexamples:• Lifting plants• Submersible pumps• Sump pumps (with and without macerator)• Drainage pumps• Agitator pumps

Gravitational heating system The next stage of development was the gravita-tional heating system. Experience showed thatto provide a room temperature of 20°C, wateronly needed to be heated to approx. 90°C, whichis just under the boiling point. The hot water roseupwards in pipelines with very large diameters.Once it had given off some of its heat (cooledoff), it flowed back to the boiler through gravity.


H I S T O R Y O F P U M P T E C H N O L O G Y

Middle Ages, to approx. 1519 AD

Double-pipe heating

Roman Empire, to approx. 465 AD

Industrial revolution, 19th Century

Modern age, 20th Century

Ceiling/wall radiant heating

In the beginning, there was fire

Roman hypocaust heating

Oven heating Gravitational hotwater heating

Wilhelm Opländer'scirculation accelerator, 1929

Single-pipe heating system

Chimney heating

Hot-air heatingof manors

Steam heating system

Underfloor heating

Evolution of the heating system

TichelmannsystemHot water circulating heating

H I S T O R Y O F P U M P T E C H N O L O G Y

10 Subject to modifications 03/2005 WILO AG

The different gravitational forces push the waterup and down.

As early as the early twentieth century, the slowstart-up of this kind of gravitational circulationsystem led to the idea of building what areknown as “circulation accelerators” into thepipelines of a heating system.

The electric motors of those days were notsuitable for use as drives, as they operated withopen slip ring rotors. These could have causedmajor accidents in a water-based heatingsystem.

Feed TV = 90 °C corresponds to G = 9,46 N

Return TR = 70 °C corresponds to G = 9,58 N

9,46 N9,58 N

Schematic of a gravitational heating system

A pump wheel in the shape of a propeller wasinstalled in a pipe elbow. It was driven by a sealedshaft which, in turn, was driven by the electricmotor.

However, no one yet thought to use the termpump for this accelerator. Only later was thisterm used in this context. This is because, as wehave already seen, pumps were associated withlifting water.

These circulation accelerators were built untilapproximately 1955, and their use allowed theheating water temperature to be lowered evenfurther.

Today, there are a variety of heating systems, themost modern of which work with very low watertemperatures. Without the heart of the heatingsystem–the heating circulating pump–heatingtechnology of this kind be impossible.

First heating circulating pumpIt was not until Swabian engineer GottlobBauknecht invented the enclosed or “canned”electric motor that it became possible to use onefor a circulation accelerator. His friend, theWestphalian engineer Wilhelm Opländer, devel-oped a design of this type, for which he wasawarded a patent in 1929.

First heating circulating pump, the “elbow pump”, model year 1929,HP type DN 67/0.25 kW


P U M P I N G S Y S T E M S

Pumping systems

Inlet

Inlet tank

Higher level tank

Ascending linegeodetic delivery head

PumpFloat valve

Float valve

Pump system for pumpingwater to a higher level

Open water pumping system

Open water pumping system Closed heating system

Circulating system using theexample of a heating system

Feed

Pump Return

Ventilation

Heat consumer

Control equipment

Diaphragm expansion tank

Closed heating system

At the right is a schematic illustration of thefunctional differences between a heating systemand a water pumping system.

While a water pumping system is an open systemwith an open outlet (a tapping point such as afaucet), a heating system is a self-enclosedsystem.

To understand the principle even more easily,consider that all the heating water does is keepmoving or circulating in the pipelines.

The heating system can be divided into thefollowing components:• Heat generator• Heat transport and distribution system• Diaphragm expansion tank for pressure

continuity and pressure control• Heat consumers • Control equipment• Safety valve

Heat generators are defined here as units such asboilers that use gas, oil, or solid fuel, as well ascirculating water heaters. They also includeelectric storage heating systems with centralwater heating, district heating stations and heatpumps.

The heat transport and distribution systemincludes all pipelines, distribution and collectionstations, and, of course, the circulating pump.The pump output in a heating system is to bedesigned only to overcome the overall resistanceof the system. The building height is not takeninto consideration, as the water that the pumpforces into the feed line pushes the water in thereturn line back to the boiler.

The schematic diagram at the left shows thecomponents that belong to a pump system thatpumps a fluid from a low-lying inlet tank to atank that is at a higher elevation. The pumptransports the water from the bottom tank tothe required height.

Here, it is not sufficient to design the capacity ofthe pump for the geodetic delivery head. This isbecause there must still be enough flow pressureat the last faucet, such as a shower on the topfloor of a hotel. The pipe friction losses thatoccur in the ascending line must also be takeninto account.

Pump delivery head = geodetic delivery head +flow pressure + pipeline losses

The individual sections of the line must be ableto be blocked off using fittings so that necessaryrepairs can be carried out. This is particularly truefor pumps, as otherwise large quantities of waterhave to be drained from the ascending linesbefore the pump is repaired or replaced.

Furthermore, float valves or other controllerunits must be provided in the lower-lying inlettank and in the higher-level tank to prevent anyoverflows.

In addition, a pressure switch can be installed atan appropriate location in the ascending line toswitch off the pump when all taps have beenclosed and no more water is being withdrawn.

The diaphragm expansion tank is responsible forcompensating for the changing water volume inthe heating system, depending on the operatingtemperatures, while simultaneously maintainingpressure continuity.

Heat consumers are the heating surfaces in therooms to be heated (radiators, convectorheaters, panel heaters etc.). Heat energy flowsfrom points at a lower temperature to points at ahigher temperature–and the greater the tem-perature difference, the quicker the flow. Thistransfer takes place by means of three differentphysical processes:• Heat conduction• Convection• Radiation.

Today, no technical problem can be solvedwithout a good control system. Thus, it is onlynatural that control units are a part of everyheating system. The most easily understood ofthese are thermostatic radiator valves for main-taining constant room temperature. Nowadays,there are also highly advanced mechanical,electrical and electronic controls in heatingboilers, mixing valves and, of course, in pumps.

Refer to the chapter on “Adjusting the pump to theheat demand,” page 35

Refer to the chapter on “Rough pump design forstandard heating systems,”page 41

Note to remember:The building height is nottaken into consideration, as the water that the pumpforces into the feed linepushes the water in the returnline back to the boiler.


Water – our means of transportIn hot water central heating systems, water is used to transport heatfrom the generator to the consumer.

The most important properties of water are:• Heat storage capacity• Increase of volume, both when heated and

when cooled• Decrease of density with increasing and

decreasing volume• Boiling characteristics under external pressure• Gravitational buoyancy

These physical properties will be discussedbelow.

An important property of every heat-carryingmedium is its heat storage capacity. Whenexpressed in terms of the mass and temperaturedifferential of the material, this is referred to asthe specific heat storage capacity.

The symbol for this is c, and the unit of measureis kJ/ (kg • K)

The specific heat storage capacity is the quantityof heat that must be transferred to 1 kg of thematerial (such as water) in order to heat it by 1°C.Conversely, the material gives off the sameamount of energy when it cools.

The average specific heat storage capacity forwater between 0°C and 100°C is:

c = 4.19 kJ/(kg • K) or c = 1.16 Wh/(kg • K)

The quantity of heat that is absorbed or givenoff Q, measured in J or kJ, is the product of themass m, measured in kg, the specific heatstorage capacity c, and the temperature differ-ence ∆� measured in K.

This is the difference between the feed andreturn temperature of a heating system. The formula is:

Q = m • c • ∆�m= V • �

V = Water volume in m3

� = Density kg/m3

The mass m is the water volume V, measuredin m3, multiplied by the density � of the water,measured in kg/m3. Therefore, the formula canalso be written as follows:

Q = V • � • c (�V - �R)

It is true that the density of the water changesalong with the water temperature. However, tomake energy considerations simpler, the calcula-tion uses � = 1 kg/dm3 between 4°C and 90°C.

The physical terms “energy,” “work” and “quan-tity of heat” are equivalent.

The following formula is used to convert Joulesinto other permitted units:

1J = 1 Nm = 1 Ws or 1 MJ = 0.278 kWh

Note: The specific heat storagecapacity is the quantity ofheat that must be transferredto 1 kg of the material (such as water) in order toheat it by 1°C. Conversely, thematerial gives off the sameamount of energy when itcools.

Specific heat storage capacity

� = Theta� = Rho


WAT E R – O U R M E A N S O F T R A N S P O R TWAT E R – O U R M E A N S O F T R A N S P O R T


Boiling characteristics of water

If water is heated past 90°C, it will boil in an opencontainer at 100°C. If the water temperature ismeasured during the boiling process, it remainsconstant at 100°C until the last drop has vapor-ised. Therefore, the constant supply of heat isused to completely vaporise the water and thusto change its aggregate state. This energy is alsoreferred to as latent (hidden) heat. If the heatcontinues to be applied, the temperature risesagain.

The condition for the sequence reflected here thata normal air pressure (NN) of 1.013 hPa must existat the water level. At any other air pressure, theboiling point moves away from 100°C.

If we were to repeat the experiment justdescribed at a height of 3000 m–for example onthe Zugspitze, Germany's highest mountain–wewould find that water already boils at 90°C. Thecause of this behaviour is the fact that the airpressure decreases at higher elevations.

The lower the air pressure on the surface of thewater, the lower the boiling temperature will be.Conversely, the boiling temperature can beincreased by increasing the pressure on thesurface of the water. This principle is used inpressure-cookers, for example.

The graphic to the right shows how the boilingtemperature of water changes depending on thepressure.

Heating systems are purposely pressurised. Thisprevents gas bubbles from forming in criticaloperating states. This also prevents air frompenetrating the water system from the outside.

All materials on the earth expand when heatedand contract when cooled. The sole exception tothis rule is water. This unique property is calledthe anomaly of water.

Water has its greatest density at +4°C, which is1 dm3 = 1 l = 1 kg.

0 6 8 10 122 4 14 16 18 20

1,0016

1,0012

1,0008

1,0004

1,0000T [C°]

Volu

me

of 1

g w

ater

[ml]

Volume change of water when heated/cooled. Highest density at 4°C: �max = 1000 kg/m3

When water is heated orcooled, its density becomeslower, meaning that itbecomes specifically lighterand the volume increases.

1,013

T [C

°]

0 3 4 5 62 [1000 hPa]pressure

150

50

0

100

100

heat volume

T [C

°]

Change in water volume

Change of aggregate state at increasing temperatures

Boiling point of water as a function of pressure

Volume increase and decrease

Water also expands when cooled to a tempera-ture below +4°C. This anomaly of water is whyrivers and lakes freeze over in winter. It is why icefloes float on the water, allowing them to bemelted by the spring sun. That would not happenif the ice sank to the bottom because it wasspecifically heavier.

However, this expansion behaviour can be per-ilous when human beings use water. For exam-ple, auto engines and water pipes explode if theyfreeze. To prevent this, antifreeze compoundsare added to the water. In heating systems,glycols are often used; refer to the manufac-turer's specifications for the proportion ofglycol.

If the water is heated or cooled from thistemperature point, its volume increases, mean-ing that its density decreases and it becomesspecifically lighter.

This can be seen quite well in a tank with meas-ured overflow.

In the tank, exactly 1,000 cm3 water are at atemperature of +4°C. If the water is heated,some of it will flow through the overflow into themeasuring glass. If the water is heated to 90°C,there are precisely 35.95 cm3, which correspondto 34.7 g, in the measuring glass.

solid

solid andliquid liquid

liquidandvapour

Transition heat (latent heat)

vapour

10 cm

4°C 90°C

10 c

m

1000 cm3 = 1 l 1000 cm3 = 1 l

Water cube of 1000 cm3

contains 1000 g at 4°C1000 cm3 water at90°C = 965.3 g

Overflow quantity 35.95 cm3 = 34.7 g


WAT E R – O U R M E A N S O F T R A N S P O R TWAT E R – O U R M E A N S O F T R A N S P O R T


Pressure

Definition of pressurePressure is the measured static pressure of fluidsand gases in pressure vessels or pipelines relativeto the atmosphere (Pa, mbar, bar).

Standing pressure Static pressure when no medium is flowing.Static pressure = level above the correspondingmeasuring point + inlet pressure in diaphragmexpansion tank.

Flow pressure Dynamic pressure when a medium is flowing.Flow pressure = dynamic pressure - pressuredrop.

Pump pressurePressure generated on the discharge side of thecentrifugal pump during operation. Dependingon the system, this value can differ from thedifferential pressure.

Differential pressure Pressure generated by the centrifugal pump toovercome the sum of all resistances in a system.It is measured between the suction and dis-charge side of the centrifugal pump. Because ofthe decrease in pump pressure due to the lossesalong the pipelines, the boiler fittings and theconsumers, the operating pressure differs ateach location of the system.

Cavitation

Cavitation is defined as the formation andimplosion of gas bubbles (cavities) as a result oflocal negative pressure formation under thevaporisation pressure of the pumped fluid at theimpeller inlet. This results in decreased output(delivery head) and efficiency, and causes roughrunning, noise and material damage to theinterior of the pump.

Through the expansion and collapse (implosion)of tiny air bubbles in areas of higher pressure (forexample, in an advanced state, at the impelleroutlet) microscopic explosions cause pressureimpacts that damage or destroy the hydraulics.The first signs of this are noise from or damageto the impeller inlet.

One important value for a centrifugal pump isthe NPSH (Net Positive Suction Head). Thisspecifies the minimum pressure at the pumpinlet that is required by this pump type to workwithout cavitation, meaning the additionalpressure required to prevent evaporation of thefluid and to keep it in a fluid state.

Pump factors that affect the NPSH are theimpeller type and pump speed. Environmentalfactors that affect it are the fluid temperature,water coverage and atmospheric pressure.

Preventing cavitationTo prevent cavitation, the pumped fluid must befed to the centrifugal pump at a certain inletheight. This minimum inlet height depends on thetemperature and pressure of the pumped fluid.

Other ways to prevent cavitation include:• Increasing the static pressure• Lowering the fluid temperature (reducing the

vapour pressure PD)• Selecting a pump with a lower maintained

pressure head (minimum inlet height, NPSH)

Positive operating pressure

Negative operating pressure

Flow pressure (dynamic pressure)

Flow pressure (dynamic pressure)

Standing pressure(static pressure)

Air pressure 1013 hPa(normal)

In heating systems In the atmosphere

Erosion, noise, burst

Positive differentialpressure

Cavitation,noise,compression

Absolute zero point

Negative differentialpressure

(+) Positive

pressure

(-) Negativepressure(suction pressure)

System pressure, pressure build-up

Operating pressure Pressure that exists or can exist when operatinga system or individual parts of it.

Permitted operating pressure Maximum value for the operating pressuredetermined for safety reasons.

Feed

Return

Ventilation

Heat consumer

Control equipment


Pump

90°C

34.7 G

The above considerations did not take intoaccount the fact that the heating circulatingpump increases the system pressure even more.

The interaction of the maximum heating watertemperature, the pump selected, the size of thediaphragm expansion tank and the responsepoint of the safety valve must be considered verycarefully. Selecting the parts of the systemrandomly – or even based on the purchase price –is never an acceptable option.

The tank is delivered filled with nitrogen. Theinlet pressure of the diaphragm expansion tankmust be adjusted to the heating system. Theexpansion water from the heating system entersthe tank and compresses the gas cushion via adiaphragm. Gases can be compressed, but fluidscannot.

Compensation for the changing water volume inthe heating system:

Illustration of a heating system with integrated safety valve

Hot water heating systems are operated at feedtemperatures of up to 90°C. The water is nor-mally at a temperature of 15°C when filled, andthen expands when heated. This increase of volume may not result in excesspressure or cause the fluid to escape.

DET inlet pressure 1.0/1.5 bar

KFEKV

(1) DET condition at installation

Nitro-gen

Water reserve DET inlet pressure +0.5 bar

KFEKV

(2) System filled /cold

Nitro-gen

(3) System at max. feed temperature

Water quantity = water reserve + expansion

KFEKV

Expansion of the heating water and protection against excess pressure

1000 cm3 = 1 l

When the heat is switched off in summer, thewater returns to its previous volume. Therefore, asufficiently large holding tank must be providedfor the expansion water. Older heating systemshave open, built-in expansion tanks. They arealways located above the highest pipeline sec-tion. When the heating temperature rises, caus-ing the water to expand, the water level in thistank also rises. Likewise, it falls when the heatingtemperature falls.

Today's heating systems use diaphragm expan-sion tanks (DET).

It must be ensured that when the system pres-sure is increased, the pipelines and other parts ofthe system are not pressurised to an extentbeyond that permitted. Therefore, it is mandatoryto equip each heating system with a safety valve.

When there is excess pressure, the safety valvemust open and blow out the expansion waterthat cannot be held by the diaphragm expansiontank. However, in a carefully designed and main-tained system, this operating state should neverhappen in the first place.

Note to remember: When there is excess pressure,the safety valve must openand blow out the expansionwater.


Design of centrifugal pumpsIn the plumbing and HVAC industries, centrifugal pumps are used inthe most varied fields. Their distinguishing features are the type oftheir design and the way they convert energy.

Self-priming and non-self-priming pumps

A self-priming pump is conditionally able tobleed the suction line, i.e. to evacuate air. Thepump may need to be filled multiple times atcommissioning. The theoretical max. suctionhead is 10.33 and is dependent on the air pressure(1013 hPa = normal).

For technical reasons, only a max. suctionhead hs of 7-8 m can be attained. This valuecontains not only the height difference from thelowest possible water surface to the suction portof the pump, but also the resistance losses in theconnection lines, pump and fittings.

When designing the pump, note that the suctionhead hs must be included in the designed deliv-ery head, preceded by a minus sign.

The suction line must be at least the same nomi-nal diameter as the pump port, or one nominaldiameter larger if possible. Its length should bekept as short as possible.

Long suction lines create increased frictionresistances that are highly detrimental to thesuction head.

The suction line should be positioned so that it isalways going uphill towards the pump. If hosematerial is used for the suction line, spiral suc-tion hoses are preferable because of its strengthand resistance to leaks. It is imperative to pre-vent leaks as otherwise damage and malfunctionof the pump may result.

For suction operation, a foot valve is alwaysrecommended to prevent the pump and suctionline from running empty. A foot valve withstrainer also protects the pump and downstreamsystems from coarse impurities such as leaves,wood, rocks, and bugs. If it is not possible to usea foot valve, for suction operation, a non-returnflap/valve should be installed ahead of the pump(pump suction port).

hs

Foot valve

Non-return flap / valve

Suction head of the pump hs

Positioning the suction line

Suction operation

Installation with foot valve ornon-return flap/valve

correct incorrect

A non-self-priming pump is not capable ofevacuating air from the suction line.

When non-self-priming pumps are used, thepump and suction line must be completely filledat all times. If air gets into the pump through leak points suchas the stuffing box of the gate valve or through afoot valve in the suction line that does not close,the pump and suction line must be refilled.

Minimum water level


D E S I G N O F C E N T R I F U G A L P U M P S

Pump efficiency

The efficiency of any machine is the ratio of itspower output to its power input. This ratio issymbolised by the Greek letter � (eta).

Since there is no such thing as a lossless drive, �is always less than 1 (100 %). For a heating circu-lating pump, the total efficiency is made up ofthe motor efficiency �M (electrical and mechani-cal) and the hydraulic efficiency �P. Multiplyingthese two values together yields the total effi-ciency �tot.

�tot = �M • �P

Depending on which of the many pump typesand sizes are examined, the efficiency can varyquite widely. For glandless pumps, the efficien-cies �tot are between 5 % and 54 % (high-efficiency pump); for glanded pumps, �tot isbetween 30 % and 80 %.

Even within the pump curve field, the currentefficiency at any given time also changesbetween zero and a maximum value.

Although a high pump pressure is generated ifthe pump works against a closed valve, becauseno water is flowing, the efficiency of the pump iszero. The same holds true for an open pipe.Although there is a large quantity of water, nopressure is built up and thus no efficiency isachieved.

Function of centrifugal pumps

Pumps are necessary for transporting fluids andfor overcoming the flow resistances encounteredin the pipe system. In pump systems with differ-ent fluid levels, this also involves overcoming thegeodetic head difference.

Because of their design and the way they con-vert energy, centrifugal pumps are hydraulic fluidflow engines. Although there is a variety oftypes, one feature shared by all centrifugalpumps is that the fluid enters an impeller axially.

An electric motor drives the pump shaft onwhich the impeller is seated. The water thatenters the impeller axially through the suctionport and the suction neck is deflected by theimpeller vanes in a radial movement. The cen-trifugal forces that affect each particle of fluidcause both the speed and pressure to increasewhen water flows through the vane area.

After the fluid exits the impeller, it is collected in the volute housing. The flow velocity is slowedsomewhat by the housing construction. Thepressure is further increased by the energyconversion.

A pump consists of the following maincomponents:• Pump housing• Motor• Impeller



Impeller types

Axial impellerSemi-axial impellerRadial impeller Radial impeller 3D

A pump never operates at a single defined point.Therefore, when designing the pump system,make sure that the duty point of the pump is inthe middle one-third of the pump curve for mostof the heating season. This will ensure that itworks in the optimum efficiency range.

The pump efficiency is determined by thefollowing formula:

Cut-away view of a glandless pump

The fluid enters the impelleraxially and is deflected radially

Pump curve and efficiency

Impellers

Impellers come in a variety of types and can beeither open or closed.

The impellers in the majority of today's pumpshave a 3D design that combines the advantagesof an axial wheel with those of a radial wheel.

Pumps with motor power P2 �totup to 100 W approx. 5 % – approx. 25 %

100 to 500 W approx. 20 % – approx. 40 %

500 to 2500 W approx. 30 % – approx. 50 %

Pumps with motor power P2 �totup to 1.5 kW approx. 30 % – approx. 65 %

1.5 to 7.5 kW approx. 35 % – approx. 75 %

7.5 to 45.0 kW approx. 40 % – approx. 80 %

Efficiency of standard glandless pumps (guide values)

Efficiency of glanded pumps (guide values)

Flow rate Q [m3/h]

H

�

Del

iver

y he

ad H

[m]

�P = Pump efficiencyQ [m3/h] = Flow rateH [m] = Delivery headP2 [kW] = Output at the pump shaft367 = Conversion constant � [kg/m3] = Density of the fluid

The efficiency (or output) of a pump depends onits design.

The following tables provide an overview of theefficiency depending on the selected motorpower and the pump design (glandless/glandedpumps).

Q • H • ��p = ------------

367 • P2

The best total efficiency of the heating circulat-ing pump is in the middle field of the pumpcurve. In the catalogues of pump manufacturers,these optimum duty points are specially identi-fied for each pump.

Pump housing

3D impeller

The output curve shows the following relation-ships: the power consumption of the motor islowest when the flow rate is also low. When theflow rate increases, the power consumptionlikewise increases. However, the power con-sumption changes at a significantly higher ratiothan the flow rate.

The effect of the motor speedIf the speed of the pump changes, but all otherconditions of the system remain the same, thepower consumption P changes roughly propor-tionately to the speed n cubed.

Based on this knowledge, the pump can becontrolled in a logical way and adapted to theheating energy demand. If the speed is doubled,the flow rate increases in the same proportion.The delivery head increases fourfold. Therequired drive energy is then multiplied byapproximately eight. If the speed is lowered, theflow rate, the delivery head in the pipe systemand the power consumption are all reduced inthe same proportions described above.

Design-related fixed speedsA distinguishing characteristic of centrifugalpump is the delivery head, which depends on themotor used and the fixed speed that is defined.Pumps with a speed of n > 1500 rpm are calledhigh-speed pumps, and pumps with a speed ofn < 1500 rpm are called low-speed pumps.

However, the motor design of low-speed pumpsis somewhat more complex, and thus they can bemore expensive. However, in situations whereuse of a low-speed pump is possible or evennecessary due to the conditions of the heatingcircuit, using a higher-speed pump would resultin unnecessarily high power consumption.Therefore, the higher purchase price of a lower-speed pump is offset by the substantial savingsof drive energy. This quickly pays back the higherinitial outlay.

By providing a controlled decrease in speedcorresponding to decreased heat demand, theinfinitely variable control of the pump electronicsprovides a significant savings.

As we have seen in a previous section, an electricmotor drives the pump shaft on which theimpeller is seated. The pressure boost generatedin the pump, and the flow rate through thepump, are the hydraulic output of the electricaldrive energy. The energy required by the motor iscalled the power consumption P1 of the pump.

Output curve of the pumpsThe output curves of centrifugal pumps areshown in a diagram: the vertical axis, the ordi-nate, plots the power consumption P1 of thepump in watts [W]. The horizontal axis orabscissa plots the flow rate Q of the pump incubic metres per hour [m3/h]. (This is also truefor the pump curve, which we will discuss later.)The scale gradations are selected based on thesame scale. In catalogues, these two curves arefrequently superimposed to clearly illustrate therelationships.



Glandless pumps

The installation of a glandless pump, either inthe feed or return, moves the water quickly andintensively. As a result, pipelines with smallerpipe cross-sections can be used. The lowers thecosts of the heating system. This also meansthat there is significantly less water in the linesof the heating system. The heating system canreact more quickly to temperature fluctuationsand can be regulated better.

FeaturesThe distinguishing feature of the impeller of acentrifugal pump is its radial acceleration ofwater. The shaft that drives the impeller is madeof stainless steel; the bearings of this shaft aremade of sintered carbon or ceramic material. Therotor of the motor, which seated on the shaft,runs in the fluid. The water lubricates the bear-ings and cools the motor.

A “can” surrounds the voltage-carrying stator ofthe motor. It is made of non-magnetisablestainless steel or carbon fibre and has a wallthickness of 0.1 to 0.3 mm.

For special applications such as water pumpingsystems, pump motors with a fixed speed areused.

If the glandless pump is used in a heating circuit,for example, and thus has to supply heat energyto the radiator, it must adjust to the changingheat demand of the house. Depending on theexternal temperature and external heat, a differ-ent quantity of heating water is required. Thethermostatic radiator valves, which are installedahead of the heating surfaces, determine thedelivery rate.



0 1 2 3 4 5 6

0 1 2 3 4 5 6

Q150

125

100

75

50

25

0

6

5

4

3

2

1

0

Wilo-TOP-S 25/5Wilo-TOP-S 30/51~230 V - Rp1/Rp11/4

0 0,5 1 1,5

0 5 10 15 20 [lgpm]

[l/s]

min. (3

)

(2)

min.

max.

0 1 2 3

0 0,5 1 1,5 2

v

[m/s]Rp1

Rp11/4

max. (1

)

[m3/h]

[m3/h]

P 1[W]

H[m

]

Relationship between pumpcurve and output curve

Power consumption of centrifugal pumps

P1 3

� �P2

n1

n2

�

Refer to the chapter on“Curves,” page 31

Refer to the chapter on“Infinitely variable speedcontrol,”page 36

Pump heating system

Wilo-TOP-S pump curve

Advantages: smaller pipe crosssections, less water content,faster reaction to temperaturefluctuations, lower installationcosts

First fully electronic glandlesspump with integrated,infinitely variable speedcontrol

Feed

Pump Return

Ventilation

Heat consumer

Control equipment


Thus, the motors of glandless pumps areswitched between multiple speeds. The speedcan also be changed manually using switches orplugs. Automation can be provided by addingswitching and control systems that operatedepending on time, pressure differential ortemperature.

Since 1988, there have been designs with inte-grated electronics that provide infinitely variablespeed control.

The electrical connection of glandless pumps,depending on the size and required pump out-put, is either 1~230 V AC or 3~400 V three-phasecurrent.

Glandless pumps feature very smooth runningand because of their design, have no shaft seal.

Today's generation of glandless pumps is built onthe modular principle. Depending on the pumpsize and required pump output, the modules arebuilt into different configurations. Therefore,any repairs that may be required can be carriedout more easily by simply replacing spare parts.

An important property of this kind of pump is thatis capable of bleeding itself at commissioning.

Pump housing

Can3D impeller

RotorWinding



Glanded pumps

FeaturesGlanded pumps are used for pumping at highflow rates. They are also better suited for pump-ing cooling water and aggressive media. Unlikeglandless pumps, the fluid does not contact themotor.

Another difference from the glandless pump isthe way the water-carrying pump housing/ shaftis sealed off from the atmosphere. This seal iscreated by a stuffing box packing or a mechanicalseal.

The motors of standard glanded pumps arenormal three-phase motors with a fixed basicspeed. They are normally controlled via an exter-nal, electronic speed control system. Today,glanded pumps are available with integratedelectronic speed control which, thanks to tech-nical developments, is available for increasinglylarge motor outputs.

The total efficiency of glanded pumps is sub-stantially better than that of glandless pumps.

Glanded pumps are divided into three differentprimary designs:

Inline pumpsPumps in which the suction port and dischargeport are in a single axis and have the same nomi-nal diameter are called inline pumps. Inlinepumps have an air-cooled and flange-mountedstandard motor.

This type of pump has proven very useful whenlarge outputs are required in building systems.These pumps can be built directly into thepipeline. Either the pipeline is held by brackets orthe pump is mounted on a foundation or a sepa-rate bracket.

Monobloc pumpsMonobloc pumps are single-speed low-pressurecentrifugal pumps in block design with a stan-dard air-cooled motor. The volute housing hasan axial suction port and a radial discharge port.Angled or motor feet are installed on the pumpsas standard equipment.

Installation positionsGlandless pumps with a nominal port diameter ofup to R 1 1/4 are supplied as screwed pumps.Larger pumps are manufactured with flangeconnections. These pumps can be installed in thepipeline horizontally or vertically without afoundation.

As mentioned previously, the bearings of thecirculating pump are lubricated by the fluid. Themedia also serves to cool the motor. Therefore,circulation through the can must be ensured atall times.

Also, the pump shaft must always be arrangedhorizontally (glandless pumps, heating). Installa-tion with the shaft standing or hanging verticallycauses unstable operating behaviour and thusrapid failure of the pump.

Refer to the installation and operating manualfor detailed information about installationpositions.

The glandless pumps we have described havegood running characteristics by virtue of theirdesign. They are relatively inexpensive to manu-facture.



Permitted without restriction for pumps with 1, 3 or 4 speeds

Permitted without restriction for pumps withinfinitely variable control

Installation positions not permitted

Installation positions for glandless pumps (partial listing)

Refer to the chapter on “Shaft seals,” page 28

Standard pumpsFor these centrifugal pumps with axial inlet, thepump, coupling and motor are mounted on thesame base plate and thus are suitable for foun-dation installation only.

Depending on the fluid and operating conditions,they are equipped with a mechanical seal orstuffing box. The vertical discharge port deter-mines the nominal diameter of these pump. Thehorizontal suction port is normally one nominaldiameter larger.

Structure of a glanded pump

Mechanical seal

Cap nut

Pump housing

Louvre

Impeller

Standard motor

Ventilator cowl



High-pressure centrifugal pumps

These pumps typically feature multi-componentdesigns with impellers and stage chambers.

The delivery rate of a pump depends on the sizeof the impeller and other factors. The deliveryhead of high-pressure centrifugal pumps isgenerated by multiple impellers/idlers arrangedin series. The kinetic energy is converted intopressure, some in the impeller and some in thedownstream idler.

Having multiple speeds allows high-pressurecentrifugal pumps to attain higher pressurelevels than single-speed, low-pressure centrifu-gal pumps are capable of.

Very large types have up to 20 speeds. Thus, theyachieve delivery heads of up to 250 m. Almost allof the high-pressure centrifugal pumps we havedescribed belong to the glanded pump family.However, manufacturers have recently also beensuccessful in equipping them with glandlessmotors.

Mechanical sealsThe basic design of mechanical seals is two ringswith highly polished sealing surfaces. They arepushed together by a spring and run againsteach other in operation. Mechanical seals aredynamic seals and are used to seal rotatingshafts at medium to high working pressures.

The sealing area of the mechanical seal com-prises two surface ground, wear-resistant faces(e.g. silicon or carbon rings), which are heldtogether by axial forces. The slip ring (dynamic)rotates with the shaft while the mating ring(static) remains stationary in the housing.

A thin film of water forms between the slidingsurfaces that serves as lubrication and cooling.

This can result in various kinds of friction of thesliding surfaces: mixed friction, boundary frictionor dry friction, of which the latter (which occurswhen there is no lubricating film) causes imme-diate destruction. The service life depends onthe operating conditions such as the composi-tion and temperature of the pumped liquid.

Stuffing boxesMaterials for stuffing boxes include high-qualitysynthetic yarns such as Kevlar® or Twaron®,PTFE, yarns made of expanded graphite, syn-thetic mineral fibre yarns as well as natural fibressuch as hemp, cotton or ramie. The stuffing boxmaterial is available by the metre or as compres-sion-moulded rings, either dry or with specialimpregnations according to the application.When the material is purchased by the metre, aring is first cut out and shaped. Then, the stuffingbox ring is installed around the pump shaft andpressed into place using the stuffing box gland.

Shaft sealsAs we have seen in the previous section, theshaft can be sealed (especially, and optionally, inthe case of standard pumps) from the atmos-phere by means of a mechanical seal or a stuffingbox packing. Following are descriptions of thesetwo sealing options.



Cut-out of a high-pressure centrifugal pump

High-pressure centrifugal pump curve

Installation positionsPermitted installation positions• Inline pumps are designed for direct horizontal

and vertical installation in a pipeline. • Enough clearance should be provided for

uninstalling the motor, louvre and impeller. • When the pump is mounted, the pipeline must

be free from tension and the pump must besupported on the pump feet (if present).

Installation positions not permitted• Installation with the motor and terminal box

facing downwards is not permitted. • If the motor power exceeds a certain level, the

manufacturer should be consulted before thepump shaft is installed in a horizontal position.

Special notes on monobloc pumps• Monobloc pumps must be installed on

adequate foundations or brackets.• Installation of monobloc pumps with the motor

and terminal box facing downwards is notpermitted. All other installation positions arepossible.

Refer to the installation and operating manual for detailed information about installa-tion positions.

Mechanical seal in a glanded pump

Note to remember:Mechanical seals are subjectto wear and tear. Dry-runningis not permissible and will leadto the destruction of thesealing faces.

Mating ring(primary seal)

Slip ring (primary seal)

Rubber bellows(secondary seal)

Spring

Impellers

Example of a high-pressurecentrifugal pump withglandless motor

Wilo-Multivert-MVIS 202-21050 Hz

[m3/h]

[l/s]0 0,2 0,4 0,6 0,8 1,0 1,2

120

110

100

90

80

70

60

50

40

30

20

10

0

Q

0 0,5 1 1,5 2 2,5 3 3,5 4 4,5

202

203

204

205

206

208

209

207

210

H[m

]


The pressure boost in the pump is called thedelivery head.

Definition of delivery headThe delivery head of a pump H is the usablemechanical work transferred by the pump to thepumped fluid, expressed in terms of the gravita-tional force of the pumped fluid under the localacceleration of gravity.

E = Usable mechanical energy [N • m]G = Gravitational force [N]

Here, the pressure boost generated in the pumpand the flow rate through the pump are depend-ent on each other. This dependence is shown in a diagram as a pump curve.

The vertical axis, the ordinate, plots the deliveryhead H of the pump in metres [m]. Other axisscales are possible. The following conversionvalues apply:

10 m = 1 bar = 100,000 Pa = 100 kPa

The horizontal axis, the abscissa, plots the scalefor the flow rate Q of the pump in cubic metresper hour [m3/h]. Another axis scale, such as litresper second (l/s), is also possible.

The curve shows the following relationships: theelectrical drive energy (taking into account thetotal efficiency) is converted in the pump intothe hydraulic energy forms of pressure boost andmotion. If the pump runs against a closed valve,the maximum pump pressure results. This isreferred to as the delivery head when Q = 0, or“H0”, of the pump. If the valve is opened slowly,the fluid begins to flow. This converts some ofthe drive energy into kinetic energy. The originalpressure can then no longer be maintained. Thepump curve begins to fall. Theoretically, thepump curve will intersect with the flow axis atthe point when only kinetic energy is transmit-ted to the water and no more pressure is built up.However, since a pipe system always has internalresistance, real pump curves end before reachingthe flow axis.

Curves Pump curve

Flow rate Q [m3/h]

Pump curve

Theoretical run

Zero-delivery head H0

Del

iver

y he

ad H

[m]

E

GH = [m]

Different flow rate andpressure changes

Flow rate Q [m3/h]

flat (e.g. 1450 1/min)

steep (e.g. 2900 1/min)

H0

H0

Del

iver

y he

ad H

[m]

Flow rate Q [m3/h]

�p

H0

H0

Del

iver

y he

ad H

[m]

Different slope, for exampledepending on the motor speedwith the same pump housingand impeller

Different flow rate and pressure changes resultdepending on the slope and changing dutypoints:• Flat pump curve

– Large change in flow rate, but small change inpressure

• Steep pump curve– Small change in flow rate, but large change in

pressure

Pump curve

Pump curve shapeThe following illustration shows the differentslopes of pump curves which can result depend-ing on the motor speed, for example.

C U R V E S


C U R V E S

The self-adjusting duty pointThe internal pipe friction resistance causes apressure drop in the pumped fluid that corre-sponds to the overall length. The pressure dropalso depends on the temperature of the flowingfluid, its viscosity, the flow velocity, the fittings,the units, and the pipe friction resistance, whichconsists of the pipe diameter, pipe roughnessand pipe length. It is shown in a system curve.The same diagram is used as for the pump curve.

System curve Duty point

Q [m3/h]

H1

Q1

H2

Q2

H [m

]

0 3 41 2

40

50

60

70

80

30

20

10

0

The curve shows the following relationships:

Pipe friction resistance is caused by the frictionof the water against the pipe walls, the frictionof the water droplets against each other, and thedirection changes in the moulded parts. Whenthere is a change in the flow rate, such as thatcaused by the thermostatic radiator valvesopening and closing, the water velocity alsochanges, and thus also the pipe friction resist-ance. Since the unchanged pipe cross-sectionmust be considered a single area of flow, theresistance changes quadratically. Therefore, adiagram will be in the shape of a parabola.

The following mathematical relationship results:

ConclusionIf the flow rate in the pipe system is halved, thedelivery head decreases to one-quarter of itsprevious level. If the flow rate doubles, thedelivery head is multiplied by four.

For example, consider the discharge of waterfrom a faucet valve. At an inlet pressure of 2 bar,which corresponds to a pump delivery head ofapprox. 20 m, water flows from a DN 1/2 faucetvalve at a flow rate of 2 m3/h. To double the flowrate, the inlet pressure must be increased from2 to 8 bar.

The point at which the pump curve and thesystem curve intersect is the current duty pointof the heating or water supply system.

This means that at this point, there is equilibriumbetween the power output of the pump and thepower consumption required to overcome theresistance of the pipe system. The pump deliveryhead is always equal to the flow resistance of thesystem. This yields the flow rate that the pumpcan supply.

It must be considered that the flow rate cannotfall below a certain minimum. Otherwise, thepump compartment can overheat, destroyingthe pump. The manufacturer's specificationsmust be followed. A duty point that is outsidethe pump curve will damage the motor.

The duty point also changes continuously due tothe changes of the flow rate during operation.The planning engineer must find a design dutypoint that matches the maximum requirements.For heating circulating pumps, this is the heatingload of the building; for pressure boosting sys-tems, this is the peak flow rate for all faucets.

All other duty points occurring in practical oper-ation are to the left of this design duty point inthe curve diagram.

The two illustrations at the right show that thechange in the duty point results from the changein flow resistance.

If the duty point shifts towards the left of thedesign point, the delivery head of the pump willnecessarily increase. This causes flow noises inthe valves.

The installation of controlled pumps adapts thedelivery head and the flow rate to the demandload. At the same time, it significantly reducesoperating costs.

System curve

Discharge from a faucet at different inlet pressures

Inlet pressure 2 barDischarge 2 m3/h

½"

2 m3

½"

4 m3

Inlet pressure 8 barDischarge 4 m3/h

Flow rate Q [m3/h]

Pump curve

both thermostatic valves are open

System curve

Intersectionpoint = Duty point

Del

iver

y he

ad H

[m]

Flow rate Q [m3/h]

Pump curve

only one thermostatic valve is open

newSystem curve(steeper)

Del

iver

y he

ad H

[m]

Intersection point =new duty point

H1 2

� �H2

Q1

Q2

=


Weather fluctuations

In the illustration to the right, the area shadedwith vertical lines makes it very clear that sea-sonal fluctuations in outside temperature requirevery different amounts of heat energy.

When the kinds of energy used for heating(wood, coal and early oil heating systems, as wellas the state-subsidised heat in the old EastGermany) were very inexpensive, it did notmatter how much fuel was used. At worst, onesimply needed to open a window or two. This isjokingly referred to as a “two-step control”-thewindow is either open or closed!

The first oil crisis in 1973 created awareness ofthe need to conserve energy.

Good thermal insulation for buildings has sincebecome a matter of course. The legal require-ments have been changing constantly to keeppace with developments in construction tech-nology. Naturally, heating technology has devel-oped at a similar pace. First to come into wide-spread use were thermostatic radiator valves,which adjust the room temperature to a com-fortable level.

The shaded area must be filledby heat energy.

Refer to the chapter on “Duty point,” page 33

The restriction of the hot water quantity causedby these valves increased the pump pressure ofthe fixed-speed pump (along the pump curve),thus causing flow noises in the valves. To solvethis problem, the overflow valve was inventedand installed as a means of releasing the excesspressure.

Jul JulOct Nov Dec JanAug Sep Feb Mar Apr May Jun

25

20

15

10

5

0

-5

-10

-15

Month

Out

side

tem

pera

ture

[C°]

Adjusting the pump to the heat demandBecause our climate has four distinct seasons, there is substantial fluctuation inoutside temperatures. From summertime highs of 20°C to 30°C, temperatures drop to -15°C to -20°C and even lower in winter. Obviously, such fluctuations are not acceptable for indoor temperatures of living quarters. In the earliest times,fire was used to heat caves. Later, heating systems were developed, as describedin the first part of "Pump Basics."

Outside temperature depending on the season

A D J U S T I N G T H E P U M P T O T H E H E AT D E M A N DA D J U S T I N G T H E P U M P T O T H E H E AT D E M A N D


Wilo-TOP-S glandless pumpwith 3 selectable speeds

Pump speed selection

So that the speed of the motors can be changed,they are constructed using different internalforcers. If less water is flowing through theheating pipes, there is also less pipe resistance,allowing the pump to work with a lower deliveryhead. At the same time, the motor power con-sumption is substantially reduced.

Since then, a wide variety of control units havebeen developed for switching heating circulatingpumps between speeds. This allows the circulat-ing pump to react directly to the room tempera-ture control. The overflow valve thus becomesunnecessary. The control units change the speedautomatically depending on the followingvariables:

• Time • Water temperature• Differential pressure• Other variables specific to the system

0 1 2 3 4 5

0 10 20 30 40 50 60 70

0 2 4 6 8 10 12 14 16 18

0 2 4 6 8 10 12 14 16 18

Q[lgpm]

600

500

400

300

200

100

0

12

11

10

9

8

7

6

5

4

3

2

1

0

[l/s]

max.

Wilo-TOP-S 40/103 ~ 400 V - DN 40

0 0,5 1 1,5 2 2,5 3 3,5 v

[m/s]

max. (1

)

(2 )min. (3 )

min.

[m3/h]

[m3/h]

P 1[W]

H[m

]

Wilo-TOP-S pump curve

Infinitely variable speed control

Infinitely variable adjustment of glanded pumpswith high motor power to heating requirementswas possible as early as the first half of the 80s.Electronic frequency converters were used tocontrol these pumps.

To understand this technology, recall the familiarcurrent frequency of 50 Hz (Hertz). This meansthat the current alternates between a plus and aminus pole 50 times a second. The rotor of thepump motor is moved at a corresponding speed.

Electronic components can be used to make the current faster or slower and thus continu-ously adjust the frequency, for example between100 Hz and 0 Hz.

However, for reasons related to the motor, thefrequency in heating systems is not reduced tounder 20 Hz or less than 40 % of the maximumspeed. Since the maximum heat output isdesigned only for the very coldest days, it willrarely be necessary to operate the motors at themaximum frequency.

While very large transformer units were stillrequired twenty years ago, a way has since beenfound to make these frequency converters smallenough to work in terminal boxes attacheddirectly to a pump, as is the case with the Wilo-Stratos.

An integrated speed control, which is infinitelyvariable and differential-pressure-sensitive,ensures that the delivery head remains constantonce it has been set. The required flow rate,which depends on weather and utilisation fac-tors, does not affect the delivery head.

Since 2001, a new technical advance has takenhold in glandless pump technology. The latestgeneration of these pumps, also called high-efficiency pumps, is able to combine enormousenergy savings with excellent efficiency usingstate-of-the-art ECM (Electronically Commu-tated Motor or permanent magnet motor) tech-nology.

Pump curve field of a Wilo-Stratos

Infinitely variable speedcontrol of the Wilo-Stratoshigh-efficiency pump

Refer to the chapter on“Glandless pumps,” page 25

� p-c

max.

[m3/h]0 2 4 6 8 10 120

2

4

6

8

10

0,50 1 1,5 2,52v

[m/s]

Wilo-Stratos 32/1-12 1 ~ 230 V - DN 32

min.

3 3,5 4

H[m

]

Pump manufacturers offer glandless pumps withmanual speed selection. As described in theprevious sections, the flow rate decreases withthe speed in adaptation to the amount of fluidallowed to pass through the thermostat andcontrol valves. This allows the circulating pump to react directly to the room temperaturecontrol.

Control modes

The electronically controlled pumps on themarket today can be equipped with electronicsthat allow various operating and control modes.

Infinitely variable speed control was possible forsmall pumps as early as 1988, but used a differentelectronic technology. The technology used atthe time, phase angle control, is comparable tothe dimmer controls used in lighting.


Here, there are control modes that the pump canexecute itself, and operating modes whereby thepump, instead of regulating itself, is adjusted tospecific duty points using commands.

The following is an overview of the most com-mon control and operating modes. Additionalcontrol units and systems can be used to processand transmit a wide variety of other data.

A D J U S T I N G T H E P U M P T O T H E H E AT D E M A N D


A D J U S T I N G T H E P U M P T O T H E H E AT D E M A N D

Variable differential pressure: ∆p-v

Constant/variable differential pressure: ∆p-cv

Manual operating mode

DDC operating mode –analogue control unit

Automatic setback mode(autopilot)

Flow rate Q [m3/h]

�p-c

nmax

ncontrolHsetpoint

½ Hsetpoint

Hsetpoint-min

Del

iver

y he

ad H

[m]

Flow rate Q [m3/h]

�p-cv

nmax

Hmin

100 %

75 %

Del

iver

y he

ad H

[m]

Flow rate Q [m3/h]

Hmax

Hmin

Tmax TmedTmin QmaxQmin

Hvar.

pos. direction

neg. direction

Del

iver

y he

ad H

[m]

The selectable control modes are:

∆p-c – Constant differential pressureThe electronics keep the differential pressuregenerated by the pump constant over the per-mitted flow rate range at the differential pres-sure setpoint HS up to the maximum pump curve.

∆p-v – Variable differential pressureThe electronics change the differential pressuresetpoint to be maintained by the pump, forexample in a linear fashion between HS and1/2 HS. The differential pressure setpoint Hincreases or decreases with the flow rate Q.

∆p-cv – Constant/variable differential pressureIn this control mode, the electronics keep thedifferential pressure generated by the pumpconstant at the set differential pressure up to acertain flow rate (HS 100 %). If the flow rate fallsbelow that, the electronics change the differen-tial pressure to be maintained by the pump in alinear fashion, for example between HS 100 %and HS 75 %.

∆p-T – Temperature-dependent differential pressure controlIn this control mode, the electronics change thedifferential pressure to be maintained by thepump depending on the measured fluid temper-ature.

Two settings are possible for this controlfunction:• Control with positive direction (pitch)

When the temperature of the fluid increases,the differential pressure setpoint is increased ina linear fashion between Hmin and Hmax. This isused, for example, in standard boilers withfloating feed temperature.

• Control with negative direction (pitch) When the temperature of the fluid increases,the differential pressure setpoint is decreasedin a linear fashion between Hmax and Hmin. Thisis used, for example, in condensing boilers inwhich a certain minimum return temperaturemust be maintained in order to achieve thegreatest possible degree of utilisation of theheating medium. To do this, it is mandatory toinstall the pump in the return of the system.

The selectable operating modes are:

Automatic setback (autopilot)The new electronically controlled glandlesspumps have an automatic setback (autopilot)function. When the feed temperature is reduced,the pump sets back to a reduced constant speed(low-load operation with fuzzy control). Thissetting ensures that the power consumption ofthe pump is reduced to a minimum and is theoptimum setting for most cases.

The autopilot setback mode may be enabled onlyif the system has been hydraulically calibrated.Failure to comply with this instruction can causeundersupplied parts of the system to freeze incase of frost.

Manual modeThis operating mode is available for electroni-cally controlled pumps that meet or exceed acertain motor power. The pump speed is set to aconstant value between nmin and nmax at theelectronics module of the pump. Manual operat-ing mode disables the differential pressurecontrol on the module.

DDC (Direct Digital Controls) and BA connection(connection to the building automation system)In these operating modes, the setpoint is trans-mitted to the pump electronics via the corre-sponding building management system. Thesetpoint is taken from the building automation(BA) system via a setpoint/actual valuecomparison, and can then be transferred as a 0-10 V/0-20mA or 2-10 V/4-20mA analoguesignal, or as a digital signal (PLR or LON interfaceon the pump).

Flow rate Q [m3/h]

HS

H

nmax = const

nmin = const

Del

iver

y he

ad H

[m]

U [V]

out

nmax

nmin

n [1

/min

]

1 1,5 3 10

Flow rate Q [m3/h]

�p-cHsetpoint

Hsetpoint-min

Del

iver

y he

ad H

[m]

Pump curves for different control modes

Temperature-dependentdifferential pressure control: ∆p-T, depending on theresulting change of the flow rate

Pump curves for different operating modes

Flow rate Q [m3/h]

�p-c

nmax

ncontrol

Hsetpoint

Hsetpoint-min

Del

iver

y he

ad H

[m]

Constant differential pressure: ∆p-c


Rough pump design for standard heating systemsThe flow rate required of a heating pump depends on the heat consumption of the building being heated. The delivery head, on the other hand, is determined by the pipe friction resistance that is present. When a new heatingsystem is installed, these variables can be easily calculated using the high-qualitycomputer programs available today. However, this calculation is more difficult when existing heating systems are renovated. Various rough estimates can beemployed to calculate the necessary pump capacity data.

When installing a new circulating pump into a heating system, its size is determinedaccording to the flow rate using the followingformula:

QPU = Flow rate of the pump in the design pointin [m3/h]

QN = Heat consumption of the area to beheated in [kW]

1.163 = Specific heat capacity in [Wh/kgK] ∆� = Design temperature difference (spread)

between heating system feed and returnin [K]; here, 10 - 20 K can be assumed forstandard systems.

Pump flow rate

QN

1,163 • ��QPU = [m3/h]

To transport the fluids to every point of theheating system, the pump must overcome thesum of all resistances. As it is very difficult todetermine the path of the pipework and thenominal diameters of the pipes used, the follow-ing formula can be used to roughly calculate thedelivery head:

R = Pipe friction loss in straight pipe [Pa/m]Here, 50 Pa/m to 150 Pa/m can beassumed for standard systems(depending on the year the house wasbuilt; older homes have a smaller pres-sure drop of 50 Pa/m due to the use ofpipes with larger nominal diameters).

L = Length of the least favourable (longest)heating line [m] for feed and return or:(length of the house + width of thehouse + height of the house) x 2

ZF = Addition factor for moulded parts/fittings ≈ 1.3Thermostatic radiator valve ≈ 1.7If these installed parts, among others,are present, a ZF of 2.2 can be used.Moulded parts/fittings ≈ 1.3Thermostatic radiator valve ≈ 1.7Mixing valve/gravity brake ≈ 1.2If these installed parts, among others,are present, a ZF of 2.6 can be used.

10,000 = Conversion factor m in Pa

Pump delivery head

R • L • ZF

10.000HPU = [m]


R O U G H P U M P D E S I G NR O U G H P U M P D E S I G N


Flow rate Q [%]

112

100

83

50 100 200

� 10 %

� 2 %

Hea

ting

out

put [

%]

Radiator operating diagramThe heat generator in a multi-family home of anolder type of construction has an output of50 kW according to a calculation or document.

At a temperature differential ∆� of 20 K(�feed = 90°C /�return = 70°C), this results in thefollowing equation:

If the same building is to be heated with asmaller temperature differential, such as 10 K,the circulating pump has to pump at twice thevolumetric flow rate, i.e. 4.3 m3/h, to transportthe required heat energy from the heat genera-tor to the heat consumers.

For our example, assume a pipe friction pressureloss of 50 Pa/m, a pipeline length for feed andreturn of 150 m and an addition factor of 2.2,since no mixing valve and no gravity brake havebeen installed in this case. This results in delivery head H:

If the building heat consumption in an unknownpipe system can only be determined using arough calculation, one might ask what effect thishas. The illustration to the right shows thetypical output curve of a room radiator.

The following relationships can be seen: if flowrate Q is decreased by 10 %, the heat output ofthe radiator decreases by only 2 %. The sameholds true if flow rate Q is increased by about10 %. In that case, the radiators will be able togive off only about 2 % more heat energy. Evendoubling the flow rate will only increase the heatoutput by about 12 %!

The reason for this is that the water velocities inthe radiators are directly dependent on the flowrate. Higher flow velocities mean a shorter dwelltime of the water in the radiator. At a lower flowspeed, the fluid has more time to give off heat tothe room.

50 • 150 • 2,2

10.000HPU = = 1,65 m

50 kW

1,163 • 20 KQPU = = 2,15 m3/h

Duty point in the pump curve field with variable volumetric flow

Wilo-EasyStar pump curves

0 0,5 1 1,5 Rp 1

0 0,25 0,5 0,75 1 Rp 1¼

v

[m/s]

6

5

4

3

2

1

00 0,5 1 1,5 2 2,5 3 3,5

Wilo-Star-E20/1-5, 25/1-5,

30/1-5 1 ~ 230 V - Rp 1/2 ,Rp 1 ,Rp 11/4

Rp ½0 31 2 4 5

[m3/h]

max.

∆ p-cv

min.

H[m

]

• Area I (left one-third) Select a smaller pump if theduty point is in this area.

• Area II (middle one-third) The pump will operate withinthe optimum range for 98 %of its operating time.

• Area III (right one-third) The controlled pump will beoperated in the leastfavourable range only whenat its design point(hottest/coldest day of theyear), i.e. 2% of its operatingtime.

Flow rate Q [m3/h]

I

II

IIIDel

iver

y he

ad H

[m]

1/3 1/3 1/3

Example of a radiatoroperating diagram 90/70°C,room temperature 20°C

Therefore, the practice of sizing pumps largerthan necessary in order to allow a so-called“safety margin” is absolutely wrong.

Even significantly under-sizing the pump hasonly relatively minor consequences: at a flow rateof 50 %, the radiators will still be able to give offapprox. 83 % heat energy to the room.

Pump planning software such as Wilo-Selectprovides a complete and effective planningservice. For tasks ranging from calculation todesign of pumps and the associated documenta-tion, it provides all the data you need.

Wilo-Select Classic is a planning software pro-gram for pumps, systems and components. It canbe used as an aid to professional work, brokendown into these menu points:

• Calculation• Design• Catalogue and article research• Pump replacement• Documentation• Electricity cost and amortisation calculations• Lifecycle costs• Data export to Acrobat PDF, DXF, GAEB,

Datanorm, VDMA, VDI, CEF• Automatic Internet update

Pump planning software

In the chapter on “Design features,” we haveseen how the efficiency curve depends on thepump curve. If this efficiency curve is consideredwhen selecting the pump, it is evident that interms of energy, the middle one-third of thecurve is the most favourable design range.Therefore, for systems with variable volumetricflow, the design point should be in the right one-third, as the duty point of the heating circulatingpump drifts into the middle one-third and staysthere for 98 % of its operating time.

The system curve becomes steeper as resistanceincrease, for example when the thermostaticradiator valves are closed.

This provides the following results from the datacalculated for delivery head H and flow rate Qaccording to the catalogue for the rough pumpdesign:

Application example Effects of the rough pump design

1.65

2.15

The duty pointmoves to area II(middle one-third).


R O U G H P U M P D E S I G N R O U G H P U M P D E S I G N


Today's circulating pumps with electronic speed control provide a very simple option forsetting the required delivery head for anunknown system:

• The prerequisite for this is that the pipelineshave been carefully calibrated and that thesystem has been bled. Open all control valves.

• The electronics of the pump feature knobs ordials for setting the delivery head. Dependingon the manufacturer, these knobs may or maynot have scaling. Begin at the lowest headsetting. Have a colleague, equipped with amobile phone or two-way radio, stand at themost distant radiator of the entire heatingsystem.

• After their initial report that no hot heatingwater is reaching this remote point, slowlyincrease the delivery head using the adjustingdial. While doing so, consider the inertia of theheating system.

• At the moment when even the most distantradiator is supplied with heat energy, thesetting process is complete.

Hydraulics from start to finish

To achieve optimum heat distribution and thelowest noise level possible, a hydraulic calibra-tion is required.

Hydraulic calibration also serves to prevent thesupply to the consumers from becoming toohigh or too low.

The nominal flow rate for supplying the lines isprovided by the pump in the pipe system. Theconsumers (such as radiators) require only aportion of that output; the portion depends onthe size and output of the radiator as well as thesetting of the thermostat and control valve.

So that each individual consumer is supplied withthe correct flow rate and pressure, differentialpressure controllers, line regulating valves,preset thermostat and control valves oradjustable return pipe unions can be installed.

Setting electronically controlled circulating pumps

For a pump to work efficiently, a hydrauliccalibration is required.

Refer to the chapter on the “Application example,”page 42

Schematic diagram of a heating system with a facility for hydraulic calibration

Line

? p 0,2 bar?

p

DV 1 DV 1

DV 2DV 2

AF

Feed

3rd floorPossible undersupply

Ground floorPossible oversupply

Return

1

�p < 0.2 bar

�p < 0.2 bar

2

Air tank at highest position of the lines

KFE valve

Thermostat valve (TV)

Return block

Gate valve

Electric actuator

Return block

Differential pressure controller (DV)

Circulating pump with pump control

Gravity brake (SB)

3-way mixer

Socla filter

Diaphragm expansion tank (DET) with KV fitting and KFE valve

Safety valve

Drainage

The settings for the consumers can be adjustedat the valves and controllers according to themanufacturer's specifications (design differen-tial pressure 40 and 140 mbar). The consumersstill need to be protected from excess pumppressure. The maximum pump pressure, forexample ahead of thermostatic radiator valves,must not exceed 2 m. If the system necessitatesthat this pressure be exceeded, differentialpressure controllers must be provided in theascending pipes so that this limit value is main-tained.

R O U G H P U M P D E S I G N



Pumps in parallel connectionIf two pumps are installed in parallel, the pumpcurves are added to each other, meaning thatwhen they operate without pressure, i.e. againstan open pipe, the flow rate is cumulative. Thusthe maximum delivery rate of two pumps of thesame size doubles.

We have already pointed out that this pumpcurve point is only a theoretical limit value.

At the other extreme, i.e. the delivery head when Q = 0, two pumps in parallel connectioncannot provide a higher delivery head than asingle pump.

The practical meaning of this is that this alsoresults in proportionate increases for both partsof the hydraulic work:• For the horizontal axis of the curve diagram, i.e.

for flow rate Q, this increase will be greater thefurther the system curve is to the right.

• For the vertical axis, i.e. for delivery head H, the increase is the greatest in the middle of thepump curves.

Each of the previous designs was based on onecentrifugal pump. In practice, however, there areoperating situations in which a single-head pumpcannot meet the requirements placed on it.

In such cases, two or more pumps are installed.Depending on the application, the pumps areinstalled in series or in parallel connection.

Before we begin our discussion of specific oper-ating functions, let us point out a fundamental(though frequently heard) error. It is, generallyspeaking, not true that two identical pumpsconnected in series pump at twice the deliveryhead, and that two identical pumps connected inparallel pump at twice the flow rate.

Although this is theoretically possible, it isimpossible to achieve in practice for reasonsrelated to the design and the system.

Pumps connected in seriesIf two pumps are connected in a row, the pumpcurves are added, meaning that if they workagainst a closed slide valve, the pressure gener-ated is cumulative. Thus the delivery head whenQ = 0 is doubled for two pumps of the same size.

At the other extreme, i.e. pumping withoutpressure, two pumps cannot transport a higherquantity of fluid than a single pump.

The practical meaning of this is that for bothparts of the hydraulic work, proportionateincreases result:• For the vertical axis of the curve diagram, i.e.

for delivery head H, this increase will be greaterthe further the system curve is to the left.

• For the horizontal axis, i.e. for the flow rate Q,the increase is extremely small.

Connecting multiple pumps

Flow rate Q [m3/h]

H1

H1 + H2

H0

2 • H0

Del

iver

y he

ad H

[m]

Series connection of twopumps installed in one housing with the same flowrate–delivery heads are addedat points of equal flow rate

Pump curve for series operation

Example of a system with multiple heating circuits

HC 1 HC 2HWG

Boiler 1

S

S

S

Flow rate Q [m3/h]Q1

Q1 + Q2

H0

2 • Q1

Del

iver

y he

ad H

[m]

Parallel connection of twopumps with the same output – actual increase ofthe flow rate

Curve for parallel connection

Wilo-Stratos D pump curve

Application example: multiple pump circuits(pumps in series connection)

For control technology reasons, large heatingsystems consist of multiple heating circuits.Sometimes, multiple boilers are also installed.

The pumps for hot water generation (HWG) andthose for heating circuits HC 1 and HC 2 workindependently of each other. The circulatingpumps are designed to overcome the respectivesystem resistances. Each of these three pumps isin series with the boiler circulating pump BCP.The task of this pump is to overcome the resist-ance that already exists in the boiler circuit.

The theoretical considerations in the precedingsection assumed pumps of the same size. How-ever, the capacity data can differ for each pump,as in the diagram shown here.

Therefore, this kind of installation presents agreat danger if the flow rates are not carefullymatched to each other. If the pump pressuregenerated by the boiler circuit pump is too high,one or all distributor pumps can receive exces-sive residual inlet pressure at the suction port.This means that they are no longer working aspumps, but as turbines (generator operation).They are being pushed. This will very quickly leadto malfunctions and pump defects. (The solutionfor hydraulic decoupling is beyond the scope ofthis discussion.)

III

Refer to the chapter on“Effects of the rough pumpdesign,” page 43

Both pumps operating

v[m/s]

10

9

8

7

6

5

4

3

2

1

0[m3/h]

Wilo-Stratos-D 50/1-8 1 ~ 230 V - DN 50

max.

∆ p-c

min.

0 5 10 15 20 25

[l/s]0 1 2 3 4 5 6 7

[lgpm]0 10 20 30 40 50 60 70 9080

0 1 2 3 4

H[m

]

+

Application example: parallel operation

When the heating energy demand reaches itshighest point, pumps I and II run together inparallel operation. In modern pumps, the controlunits required for this are contained in plug-inmodules or in the electronic module with corre-sponding accessories.

Since each of the two single-head pumps builtinto the twin-head pump can, in turn, beadjusted in multiple steps, a wide spectrum ofpossibilities exists for adjusting the pump to theheat demand.

This is shown by the following curve. The dashedline is the pump curve for individual operation ofone of the two pumps. The thick black line is theshared pump curve in duty/assist operation.

If one pump fails, over 50 % of the flow rate isstill pumped. According to the radiator operatingdiagram, this still means a heat output of morethan 83 % that can be given off by the radiator.

Parallel connection of two pumps with the same output



To keep the operating times of the pumps asuniform as possible, the role of controlled mainpump is assigned to different pump each day ona rolling basis.

The bottom diagram shows the great savings,including those of power consumption, that arepossible depending on the type of each pump.

In large systems, the advantage of many years oflow operating costs is more important than smallinitial investment costs. Four small pumps withbuilt-in electronics and control units can costmore than one large pump without a control unit.However, if we take an operating time of tenyears as an example, the investment costs forthe control system and pumps with integratedelectronics can be recouped several times overby the savings achieved. An additional sideeffect is better supply of the system, which isalso quieter and more cost-effective, because ofthe improved supply to the consumers. This caneven bring about a significant primary energysavings.

Application example: main and standby pump

The purpose of a heating system is to heat livingspaces in the cold season. Therefore, the provi-sion of a standby pump in each heating circuit isrecommended in the event that the other pumpbreaks down. This is true, for example, for multi-family homes, hospitals and public institutions.

On the other hand, installing a secondpump–along with the necessary fittings andcontrols–results in significantly higher installa-tion costs. The industry offers a good compro-mise in the form of twin-head pumps. Twoimpellers and their drive motors are enclosed inone housing.

In duty/standby operation, pumps I and II run inalternation according to a timed schedule (forexample, 24 hours each). While one pump isrunning, the other is idle. The butterfly valve,which is built in as standard equipment, preventsfluid from flowing back through the pump whenit is at standstill.

As described at the beginning of this section,failure of one of the pumps triggers an automaticfault switchover to the pump that is ready foroperation.



Peak-load operation with multiple pumpsMultiple, individual partial-load pumps areinstalled in systems that require a large flow rate.An example would be a hospital with 20 buildingsand a centrally located boiler house.

In the following example, large glanded pumpswith integrated electronics are installed parallelto each other. Depending on the requirements,such peak-load systems can consist of two ormore pumps of equal size.

In conjunction with the signal transmitter, thecontrol system maintains constant total pumppressure (∆p-c).

In this regard, the flow rates allowed through bythe thermostatic radiator valves at all radiators,and how many of the four pumps are currentlyoperating, are completely unimportant.

If a system of this sort is hydraulically calibrated,these circuits are also used to perform a remotepoint evaluation that ensures the proper supply.For this evaluation, the signal transmitter isinstalled at the point of the system that is mostdifficult to supply (at a distant, or remote point).The control signal from the signal transmitter isthen sent to the control unit, where it is adjustedfor the inertia and other characteristics of thesystem. The connected pumps are, in turn,activated by the control unit, for example viatheir integrated electronics.

III

I II

Pump I or pump II operating

Controller

Differential pressure indicator

Flow rate V [%]

PH+PS1PH

n = 60%

�40

�6

25

50

75

100

�� = const.

n = 4x100%n = 60%

PH + PS1 + PS2

PV

PT1

PT3

PT2

Del

iver

y he

ad H

[m]

Pow

er c

onsu

mpt

ion

P [%

]

V T1 �25% V T2 = 50% V T3 = 75% V V = 100%

Multiple-pump system with infinitely variable controlThe complete system shown in the example iscontrolled as follows:The base duty or main pump PH with integratedelectronics is controlled continuously betweenits maximum speed of n = 100 % and a minimumspeed of n = 40 %, triggered by the differentialpressure signal transmitter. This causes thepartial-load flow rate to move smoothly in therange of QT1 < = 25 %. If a flow rate QT > 25 % isrequired, the first peak-load pump PS1 isswitched on, also by its integrated electronics.The control of the main pump PH continues to beinfinitely variable, so that its effect likewiseadjusts the total flow rate between 25 % and50 % according to the demand.

This process is repeated when the partial-loadpumps with integrated electronics PS2 and PS3are switched on, each at full speed. The maxi-mum heat demand of the entire hospital iscovered when all four pumps are working at theirhighest output, as they then provide the peak-load flow rate VV. Similarly, the peak-load pumpswith integrated electronics, PS3 to PS1, areswitched off again when the heat demanddecreases.

Legend:PH = Main pumpPS = Peak-load pump 1-3VV = Full-load flow rateVT = Partial-load flow ratePV = Full-load power

consumptionPT = Partial-load power

consumption


Questions on these topics:• Water supply• Wastewater disposal• Heating technology

Question 1:• Pumps existed as early as ancient times. (1)• Pumps were invented for heating. (2)• Pumps can be used to pump water only. (3)

Question 2:• Archimedes invented the scoop wheel. (1)• The Chinese invented the centrifugal pump. (2)• The incline of Archimedes' screw determines

the delivery quantity. (3)

Question 3:• The first sewers were built in 1856. (1)• The Cloaca Maxima was built in Rome. (2)• Lifting plants must be installed at all drains. (3)

Question 4:• The ancient German peoples already

had central heating. (1)• The Romans already built floor-heating

systems. (2)• Steam engines were used to heat

homes in the 17th century. (3)

Question 5:• The term “gravitational heating systems”

refers to the heaviness of the powerful pumps they use. (1)

• Steam heating systems work at temperatures between 90°C and 100°C. (2)

• Low-temperature heating systems are possible only because of circulating pumps. (3)

Question 6:For which application have pumps already beenused for centuries?• Water delivery (1)• Steam heating systems (2)• Gravitational heating systems (3)

Question 7:• The circulation accelerator, which was

patented in 1929, was a further development of a frequently used heating pump. (1)

• It was the first pump for pipe installation in heating systems. (2)

Question 8:To which part of the human body can heatingcirculating pumps be compared?• The arms (1)• The heart (2)• The head (3)

Question 9:The advantage provided by the heatingcirculating pump is:• Lower installation costs (1)• Controlled operating costs (2)• Adaptable control (3)• All of the above (4)

Did you know...Test your knowledge of the “Fundamental principles of pump technology” by taking this short quiz.

History of pump technology

ConclusionBeginning with early developments and the most basic context, and continuing with highly complex examples, the “Fundamentalprinciples of pump technology” are intended to provide an overviewof how and where pumps can and should be used.

It illustrates the complex relationships and interconnections ofpump operation, as well as the improvements in operation madepossible by today's electronic control systems.

Compared to a building's heating system, the circulating pump isone of the smallest components of the overall system in terms ofsize and purchase price. It is the pump, however, that allows all theother components to function properly. If we compare the system tothe human body, there can be no doubt: the pump is the heart ofthe system!

Answers:Question 1:No. 1Question 2:No. 3Question 3:No. 2Question 4:No. 2Question 5:No. 3Question 6:No. 1Question 7:No. 2Question 8:No. 2Question 9:No. 4


D I D Y O U K N O W. . .

Design features

Question 1:Which of the following statements are true of the suction head?• It depends on the air pressure. (1)• Theoretically, it is 10.33 m. (2)• It has an effect on the delivery head. (3)• Statements 1-3 are all true. (4)

Question 2:Which of the following statements is true ofself-priming pumps?• They are conditionally able to bleed

the suction line. (1)• The suction line should be kept as

short as possible. (2)• They must be filled before commissioning. (3)• All of the above are true. (4)

Question 3:What function does the heating water inside the “can” of glandless pumps have?• It cools and lubricates. (1)• It supports the delivery head. (2)• It has no real function. (3)

Question 4:What are the benefits of a glandless pump?• Good efficiency (1)• High heating circuit temperatures (2)• It runs smoothly and is maintenance-free. (3)

Question 5:What is the recommended installation positionfor an inline glanded pump?• Installed with the shaft arranged vertically. (1)• Installed with the shaft arranged

horizontally. (2)• Other than the motor facing down,

any installation position can be chosen. (3)

Question 6:Upon which of the following factors does theamount of heat energy available in the waterdepend?• The storage capacity of the water. (1)• The mass of the water being moved. (2)• The difference in temperature between

the feed and return (3)• It depends on all three of the

above variables. (4)

Question 7:Which of the following makes gravitationalheating systems work better? • Smaller pipe resistances (1)• Larger pipe resistances (2)

Question 8:Which of the following is the role of the safety valve?• It is used to ventilate and bleed the system. (1)• It protects the system from an excessive

pressure load. (2)• None; it is useless when

electronic pumps are installed. (3)

Question 1:When does water expand?• When it is heated above 0°C. (1)• When it is cooled below 0°C. (2)• When it is heated or cooled from a

temperature of +4°C. (3)

Question 2:Which of the following are three equivalent terms?• Work, output and efficiency (1)• Work, energy and quantity of heat (2)• Work, vim and vigour (3)

Question 3:Which of the following is true of water when heated?• It becomes specifically lighter. (1)• It becomes specifically heavier. (2)• Its density remains the same. (3)

Question 4:What happens to the water temperature when it reaches the boiling point?• It continues to increase. (1)• It stays at the boiling point. (2)• It begins to fall. (3)

Question 5:How can cavitation be prevented? • By selecting a pump with lower

maintained pressure head. (1)• By decreasing the static pressure. (2)• By increasing the vapour pressure PD. (3)



Water – our means of transport

Questions on these topics:• Heat storage capacity • Volume increase and decrease• Pressure

Questions on these topics:• Self-priming and non-self-priming pumps• Glandless pumps• Glanded pumps

Question 6: For which application are glanded pumps used?• Low flow rates (1)• High flow rates (2)• No motor lubrication (3)

Question 7:Which of the following ratios is equivalent to the efficiency of the pump?• The ratio of the discharge port

to the suction port (1)• The ratio of the drive power to the

output power (2)• The ratio of its power intake to its

power output (3)

Question 8:Which area represents the highest efficiency of a centrifugal pump?• The left one-third of the pump curve (1)• The middle one-third of the pump curve (2)• The right one-third of the pump curve (3)

Question 9:Which of the following statements is true ofmechanical seals?• They consist of hemp or synthetic fibres. (1)• They are shaft bearings. (2)• They are used in glanded pumps. (3)

Answers:Question 1:No. 3 Question 2:No. 2Question 3:No. 1Question 4:No. 2Question 5:No. 1Question 6:No. 4Question 7:No. 1Question 8:No. 2



T O P I C

Adjusting the pump to the heat demand

Questions on these topics:• Weather fluctuations• Pump speed control• Infinitely variable speed control• Control modes

Question 1:Which of the following is true of the heatdemand of a building?• It always remains the same. (1)• It changes with the season. (2)• It increases from year to year. (3)

Question 2:What happens when the heat demand changes?• The thermostatic radiator valves

are adjusted. (1)• The windows are adjusted

(= opened/closed). (2)• The system pressure adjusts itself. (3)

Question 3:Why is the speed of pumps changed?• To adjust to the required flow rate. (1)• To relieve the overflow valve. (2)• To compensate for errors

in the pump design. (3)

Question 4:How is the pump speed changed?• Always manually (1)• Always automatically (2)• Either manually or automatically

depending on the equipment (3)

Question 5:Which of the following are true of Infinitelyvariable speed control? • It is better than step control. (1)• It is worse than step control. (2)• It provides the same results as step control. (3)

Question 6:Which of the following can be adjusted withelectronically controlled circulating pumps?• The heat demand (1)• The service life (2)• The delivery head (3)



Curves

Question 1:Which of the following statements is true ofelectrical drive energy? • It is converted into high pressure. (1)• It is converted into pressure boost

and motion. (2)• It is gained from hydraulic energy. (3)

Question 2:What is plotted on the axes of the curve diagram?• The delivery head on the vertical axis and

the flow rate on the horizontal axis. (1)• The flow rate on the vertical axis and the

delivery head on the horizontal axis. (2)• The energy on the vertical axis and the

medium on the horizontal axis. (3)

Question 3:What does the system curve show?• The increase in resistance over the flow rate (1)• The increase in the flow rate over

the pressure (2)• The change in the flow rate with

the water velocity (3)

Question 4:How does pipe friction resistance change? • In a linear fashion with the flow rate (1)• Quadradically with the flow rate (2)• Cubically with the flow rate (3)

Question 5:Which of these has to be considered in designing the delivery head that is supplied by aheating circulating pump?• The height of the building (1)• The pipe network resistance (2)• Both of the above variables (3)

Question 6:Which of these has to be considered in designing the flow rate that is supplied by aheating circulating pump?• The average outside temperature (1)• The desired inside temperature (2)• The calculated heat demand (3)

Question 7:Which of the following is true of control mode ∆p-c = differential pressure?• The flow rate is increased by a

constant speed. (1)• The speed adjusts to the required flow rate. (2)• The diaphragm expansion pressure tank

inlet pressure remains constant at all times. (3)

Question 8:Which of the following is true of automaticsetback mode (autopilot)?• It is controlled by a timer. (1)• It depends on the room temperature. (2)• It may be enabled only in hydraulically

calibrated heating systems. (3)

Question 9:Which of the following is true of the latest ECMpump technology (high-efficiency)?• The rotor consists of a permanent magnet. (1)• It provides up to an 80 %

savings in operating costs compared to conventional pumps. (2)

• The rotation of the rotor is generated by an electronic commutation (frequency converter). (3)

• Points 1–3 mean that is the most cost-saving glandless pump currently available. (4)

Questions on these topics:• Pump curve• System curve/pipe system curve• Duty point

AnswersQuestion 1:No. 2Question 2:No. 1Question 3:No. 1Question 4:No. 2Question 5:No. 2Question 6:No. 3




Questions on these topics:• Pump flow rate• Pump delivery head• Pump design• Hydraulic calibration



Question 1:How should a heating circulating pump be selected?• According to the specified nominal diameter. (1)• According to price considerations. (2)• According to the capacity data. (3)

Question 2:What happens when the flow rate is increased by 100 %?• The heat output decreases by approx. 2 %. (1)• The heat output increases by approx. 12 %. (2)• The heat output remains the same. (3)

Question 3:What should one do when in doubt as to which heating pump to select?• Select the smaller pump. (1)• Select the larger pump. (2)• Select the less expensive pump. (3)

Question 4:For which of the following variables should thepump in a water pumping system be designed?• The geodetic head (1)• The residual flow pressure (2)• The pipe friction resistances (3)• The sum of variables 1 to 3 (4)

Question 5:In heating systems, for which of the followingvariables must the delivery head be designed?• The geodetic head (1)• The residual flow pressure (2)• The pipe friction resistances (3)• The sum of variables 1 to 3 (4)

Rough pump design

Questions on these topics:• Pumps in series connection• Pumps in parallel connection• Peak-load operation with multiple pumps

Question 1:What happens when two pumps are connected in series?• The delivery head doubles. (1)• The flow rate doubles. (2)• The change depends on the position

of the system curves. (3)

Question 2:What danger exists when pumps are connected in series?• It will operate as a generator,

and the pump will be “pushed.” (1)• The pump outputs will be reduced to zero. (2)• It will cause an undersupply of the system. (3)

Question 3:What happens when two pumps are connected in parallel?• The delivery head doubles. (1)• The flow rate doubles. (2)• The change depends on the system curves. (3)

Question 4:In which mode can twin-head pumps be operated?• Primarily in duty/standby operation (1)• Primarily in duty/assist operation (2)• It can be operated in both of these modes. (3)

Question 5:In large systems, what benefit is provided bydividing the required pump output over multiplepumps?• Lower operating costs (1)• Longer service life of the pumps (2)• Both statements 1 and 2 are true. (3)

Connecting multiple pumps

Question 6:What is the name of the control mode in whichthe signal transmitter is installed in the systemat a great distance from the switching device?• Centre of gravity control (1)• Difficult control (2)• Remote point control (3)

Question 7:Which of the following should be considered when connecting pumps in parallel to one control unit?• The pumps should be the same size. (1)• They should all be low-speed pumps. (2)• They should all be high-speed pumps. (3)

Answers:Question 1:No. 3Question 2:No. 2Question 3:No. 1Question 4:No. 4Question 5:No. 3Question 6:No. 4Question 7:No. 5

Answers:Question 1:No. 3Question 2:No. 1Question 3:No. 3Question 4:No. 3Question 5:No. 3Question 6:No. 3Question 7:No. 1

Question 6:Why are heating systems calibrated?• To achieve optimum heat distribution. (1)• So that the system will operate as

quietly as possible. (2)• To protect the consumers are from

undersupply or oversupply. (3)• All three of the above points are

correct and important. (4)

Question 7:When the required delivery head is unknown,what is the correct procedure for adjusting anelectronic pump?• The best way is with the help of a colleague. (1)• Adjustment is done after careful

ventilation and hydraulic calibration of the system. (2)

• The adjustment process begins at the lowest setting of the pump. (3)

• It continues until there is an adequate supply of heat energy to the most distant radiator. (4)

• Adjustment is finished when all four of theabove steps have been completed. (5)

Controller

Differential pressure indicator


Informational materials

Physical Symbol Legal units of measure Units of Recommended Remarksvariable SI units Other legal measure no units

units of measure longer(incomplete listing) permitted

Length l m Metre km, dm, cm, m Basic unitmm, �m

Volume V m3 dm3, cm3, mm3, cbm, cdm, … m3

Litre (1 l = 1 dm3)Flow rate, Volu- Q m3/s m3/h, l/s l/s andmetric flow rate V m3/sTime t s Second s, ms, �s, ns, … s Basic unit

min, h, dSpeed n rps rpm rpmMass m kg Kilogram g, mg, �g, Pound, kg Basic unit

Ton Hundred- The mass of an item of (1 t = 1,000 kg) weight merchandise is called

its weight.Density � kg/m3 kg/dm3 kg/dm3 The designation

and kg/m3 “specific weight” shouldno longer be usedbecause it is ambiguous(see DIN 1305).

Force F N Newton kN, mN, �N, … kp, Mp, … N 1 kp = 9.81 N. The (= kg m/s2) gravitational force is

the product of the massm and the local acceleration of gravity g.

Pressure P Pa Pascal Bar kp/cm2, at, bar 1 at = 0.981 bar(= N/m2) (1 bar = 105 Pa) m head of = 9.81 • 104 Pa

water, Torr, … 1 mm Hg = 1.333 mbar1 mm head of water

= 0.098 mbarEnergy, W, J Joule kJ, Ws, kWh, … kp m, J and kJ 1 kp m = 9.81 JWork, Q (= Nm 1 kW h = 3,600 kJ kcal, cal 1 kcal = 4.1868 kJQuantity of heat = Ws) WEDelivery head H m Metre M Fl. S. m The delivery head is

the work performed on the unit of massof the fluid in J = N m,expressed in terms of the gravitational force of this unit of mass in N.

Power P W Watt MW, kW kp m/s, kW 1 kp m/s = 9.81 W(= J/s horsepower 1 horsepower = 736 W= N m/s)

Temperature- T K Kelvin °C °K, deg. K Basic unitdifference

Legal units of measure, partial listing for centrifugal pumps

System knowledge

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Planungssoftware für Pumpen,Pumpensysteme und Komponenten

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WILO AG has invested the greatest care into preparing all of the texts in this brochure. Still, thepossibility of errors cannot be excluded. The publisher expressly disclaims any and all liabilityregardless of legal basis.

Copyright 2005 by WILO AG, DortmundThis work and all of its parts are protected by copyright. Any kind of use outside the narrow limitsof copyright legislation without the consent of WILO AG is improper and punishable by law. Thisapplies particularly to duplication, translation, microfilming, and any other kind of processing, aswell as storage and processing in electronic systems. This also applies to the use of individualillustrations and excerpts from the text.

Fourth, revised and updated edition 2005

Basic of Pumps

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