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Pressure Booster Systems – Designers Handbook

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CHAPTER 1: The Domestic Pressure Booster System

SECTION I: WHY IS IT REQUIRED?

The pressure booster package is required when available street main pressure is notsufficient to serve the building. This pressure deficiency can be caused by a number ofdifferent reasons. Below are some of the most common:• Loss of street pressure due to increased area population or development.• Pressure loss due to the installation of a backflow preventer.• Large flow volumes such as stadiums and office buildings reduce main pressure

available.• Aging piping which causes “fouling” thereby restricting flow through the pipe.• Requirements within the building for minimum fixture pressures in order to achieve

optimum performance.

The booster system takes the existing street pressure and increases it to the preferred“System Pressure”. System Pressure refers to the pressure in the piping manifold after thepressure booster. It can be expressed by the following formula:

Suction Pressure + Boost Pressure - PRV Losses = System Pressure

Where “suction pressure” is the available street pressure, “boost pressure” is the requiredadditional increase added to the street pressure and PRV Losses are the pressure loss

through the pressure reducing valves & the booster system piping.

Relationship of Boost Pressure vs. System Pressure. Boost Pressure is what we design for. Supplypressure is that which is currently available. Combined, these form System Pressure.

TIP: Suction pressure can usually be obtained from a copy of the “Fire Flow Test” whichprovides suction pressures at various flows. Use the maximum system design flow todetermine minimum suction pressure.

Residual Pressure

PRV Losses

Static Pressure (height)

Friction Loss

Supply Pressure (from City)

BOOST

Supply + Boost = System Pressure


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SECTION II: INFORMATION REQUIRED

There are minimum informational requirements in order to properly size a Booster package:• Suction Pressure: mentioned in the previous section, current service available from the

local municipality.• Building Height: can be determined by number of stories (indicate distance between

each level), or height can be taken off architectural elevations.• Friction Loss: can be figured based on pipe distance or 10% of building height.• Loss through Booster Package: Generally based on 5 PSI for the PRV’s and

interconnecting piping in the package (12 Feet TDH).• Residual Pressure: how much pressure is required at the top of the structure after

everything else is accounted for (i.e. pressure at the highest fixture).

SECTION III: SYSTEM CONFIGURATIONS

Systems are available in the following most common configurations:• Simplex = 1 pump system: One pump produces all flow and pressure• Duplex = 2-pump system: System flow is usually split amongst (2) pumps, equally and

un-equally.• Triplex = 3-pump system: System flow is usually split among (3) pumps, equally and

un-equally.• Quadraplex = 4-pump system: Large system flows are split among (4) pumps, typically

un-equally.


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CHAPTER 2: The Plumbing System

SECTION I: SIZING REQUIREMENTS

Establish building dimensions• Building height can be determined either by architectural drawings or # of floors times

height/floor. (ex: 10 floors x 10 feet/floor = 100’ Tall)• Convert feet of water column to PSI by using the following formula:

H x .433 = PSI

where H = Static Head; .433 is the mathematical reciprocal of 2.31, therefore,

you will arrive at the same condition by dividing TDH by 2.31)

The table to the leftindicates the variousrequirements inestablishing systempressure rating.Typically, all figures areexpressed in PSI usingthe Feet/PSI conversionformula and are thenconverted back to TDH toselect the pumps.

Establish building flow capacity (see fig. #3 & 4)• Count the number of fixtures which use domestic water. Bear in mind that different fixtures

use water differently. (ex: 1.6 GPF Water Closet, 3.5 GPF Water Closet, Flush Valve, etc.)• Determine the “type” of building from the flow chart which will indicate maximum required

GPM.• Be careful when selecting systems with a constant load, these systems will not benefit from

a drawdown tank and system shutdown. (ex: Cooling tower, commercial laundry facilities,restaurants, night clubs, hydronic water make-up, etc.)

TDH PSIA. STATIC HEAD - BUILDING HEIGHTB. FRICTION HEAD - FRICTION LOSSC. RESIDUAL PRESSURE REQUIRED (@ TOP)D. SYSTEM REQUIRED PRESSURE (A + B + C)E. MINIMUM SUCTION PRESSURE (SUBTRACT)F. SYSTEM BOOST PRESSURE (D - E)G. PRV LOSSES (5 -10 PSI)H. PUMP HEAD REQUIRED (F + G)


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WATER SUPPLY FIXTURE UNITS - WSFU

Heavy Use AssemblyOther than Dwelling Units

Serving Three or more Dwelling UnitsIndividual Dwelling Units

TYPE OF FIXTURESBathroom Group, 1.6 GPF Gravity Tank Water Closet 5.0 3.5Bathroom Group, 1.6 GPF Pressure-Tank Water Closet 5.0 3.5

Bathroom Group, 3.5 GPF Gravity Tank Water Closet 6.0 5.0Bathroom Group, 1.6 GPF Flushometer Valve 6.0 4.0

Bathroom Group, 3.5 GPF Flushometer Valve 8.0 6.0

Kitchen Group (Sink and Dishwasher) 2.0 1.5Laundry Group (Sink and Clothes Washer) 5.0 3.0

INDIVIDUAL FIXTURESBathtub or Combination Bath/Shower 4.0 3.5

Bidet 1.0 0.5

Clothes Washer, domestic 4.0 2.5 4.0

Dishwasher, domestic 1.5 1.0 1.5

Drinking Fountain or Watercooler 0.5 0.75

Hose Bibb (1/2" Supply Pipe) 2.5 2.5 2.5

Hose Bibb, each additional (1/2" Supply Pipe) 1.0 1.0 1.0

Kitchen Sink, domestic 1.5 1.0 1.5

Laundry Sink 2.0 1.0 2.0

Lavatory 1.0 0.5 1.0 1.0

Service Sink or Mop Basin 3.0Shower 2.0 2.0 2.0

Shower, continous use 5.0

Urinal, 1.0 GPF 4.0 5.0

Urinal, greater than 1.0 GPF 5.0 6.0

Water Closet 1.6 GPF Gravity Tank 2.5 2.5 2.5 4.0

Water Closet 1.6 GPF Pressure Tank 2.5 2.5 2.5 3.5

Water Closet 1.6 GPF Flushometer Valve 5.0 5.0 5.0 8.0

Water Closet 3.5 GPF Gravity Tank 3.0 3.0 5.5 7.0

Water Closet 3.5 GPF Flushometer Valve 7.0 7.0 8.0 10.0

Whirlpool Bath or Combination Bath/Shower 4.0 4.01995 Change to the National Standard Plumbing Code adopted at NSPC Public Hearing - August 1994

Typical Fixture Unit Chart showing various types of fixtures and their relational fixture unit

assignment. This is typically used by consultants to determine a fixture unit “load” whichis interpreted on the building profile curves (fig. #4). This chart is taken from the

National Plumbing Code, August 1994.


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Fixture Unit Chart

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Total Fixture Units

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GPM

Hunters'Curve

Hospitals

Schools/DormsOffices, Hotels, Low RentHigh-Density Apartments

The plumbing designer must consider the activities of the occupants and the building usage.Since this does not consider the human element, we rely on operating data and records compiledover the years by users, manufacturers and trade associations. The graph above is arepresentation of this information. This is typically what system flows are based on.

The National Bureau of Standards published report BMS-65, “Methods of Estimating Loads in

Plumbing Systems”, by the late Dr. Roy B. Hunter. This report provided tables of load-producing characteristics (fixture unit weighting) of commonly used domestic water fixtures aswell as probability curves to estimate the capacity of the system. These curves are the basisfor all manufacturers selection of Pressure Booster Systems. Over the years, the industry hasfurther defined the “Hunters Curve” changing the probability of maximum flow in accordancewith the type of building, since all structures do not use water in the same manner andfrequency.

Special ServicesDon’t forget that there are sometimes other systems which rely on the plumbing pumps forwater make-up, service load, etc. These must be added in after you have determined thedomestic fixture load. Examples of this are:

• Cooling Tower make-up water valve• On-Site commercial laundry facility (Hospitals, Hotels, Dorms, etc.)• HVAC System make-up load• Boiler water make-up load• Swimming pools

Add these services in addition to the GPM arrived at from the charts.

TIP: Remember that when you add for special services, you will not have fixture unit references. You mustadd in the additional flow rate in gallons per minute AFTER you have used the fixture unit method toarrive at a total system flow rate. When this step is complete, simply add the additional GPM to the totalsystem capacity for the extra services.


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SECTION II: SYSTEM CONDITIONS Establish current water system conditions• Minimum suction pressure; this can typically be found on the Fire Flow Test, which is done

on all buildings which require a fire system. Use the maximum design flow based on theflow condition calculated from fixture unit count. DO NOT ASSUME A MINIMUMSUCTION PRESSURE! Get this information from consultant or contractor.

• On “cistern” systems, be careful when you have a low NPSH. Suction lift is notrecommended for a pressure booster system.

• Figure #5 through #7 explains the potential problems which can arise when an accuratesuction pressure is not used to size the booster package.

TIP: In some cases, an incorrect suction pressure can contribute to potential problems. For example: If a

system is designed using a minimum suction pressure of 20 PSI and a potential pump shutoff pressureof 140 (@ 0 GPM Flow), the capacity of the system could exceed minimum ratings if the suctionpressure exceeds 40 PSI! In this case, the system will now EXCEED the 175 PSI working pressure,thereby, requiring a HIGH PRESSURE system design.

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50 100 150 200 250 300 350 GPM0

PSI

Design Suction Pressure20 PSI

X

Design Condition

Shut-off Pressure

Design FlowPump Boost

Pump design head is based on the minimumavailable (worst case) suction pressure plus thepump boost

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60

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50 100 150 200 250 300 350 GPM0

PSI

Design Suction Pressure20 PSI

X

Shut-off Condition

Shut-off Pressure

Total PumpPressure System

WorkingPressure

Additional head is achievable when pump moves toshut-off. Although the PRV’s will regulatedownstream, upstream pressures can rise.

In a worst case scenarioas shown in the graphicto the left, when suctionpressures are under-estimated, there is apotential that the pressurecould exceed the systemrated working pressure.

20

60

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50 100 150 200 250 300 350 GPM0

PSI

Design Suction Pressure

Actual Suction Pressure

20 PSI

60 PSI

X

X

Design ConditionShut-off Pressure

W.P. #1

W.P. #2Additional PressuresDangerously High!


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SECTION III: FLOW SPLIT

Select the best capacity split for the GPM capacity.• In some cases, it is best to use an un-equal split rather than an equal capacity split. Much

of this can be determined by either flow analysis (flow recorder mounted on system for aperiod of time in order to develop a usage pattern) or by some other less technical means.(i.e.: Typical load does not exceed 20% of system capacity for 70% of the day)

Select a system manifold suited for the conditions and maximum flowArmstrong offers a number of different manifold materials to suit nearly every domestic waterneed. They are as follows:• Cast Iron Flanged on either end. (includes (2) blind flange caps)• Type “K” Copper Manifolds on Series 6500 (due to pump weight)• Type “L” Copper Manifolds available on all other models• Type 304 Schedule 10 Stainless Steel fabricated• Schedule 40 Galvanized Steel fabricated

Size manifolds according to the total system flow rate.• See Figure #7 below for maximum recommended flows for system headers:

Manifold Size Maximum Flow (GPM)3” 3004” 5006” 10008” 2000

10” 3000Fig. 7: The above chart represents the maximum recommended flow rates through thePressure Booster System headers for various manifold sizes.

Rule of Thumb:

Duplex Systems - Un-equal split (33%/67%) becomes more cost effective at 200 GPM or higher.

Triplex Systems - Un-equal split (20%/40%/40%) is more cost effective at 300 GPM or higher.


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PROBLEM 1:

1. Apartment building: 15 stories, 10’/story = __________ X .433 = __________ PSI

2. Minimum suction pressure available is 30 PSI.

3. System is a “retro-fit” constructed in 1975 utilizing 3.5 GPF Water Closets.

4. There are 2.5 Baths/Unit, 5 Units per floor, each with a laundry room & kitchen.

5. Total # of Flow units = _______ Based on High Density Apartment Profile = _______ GPM.

6. There is a cooling tower on the roof which has a constant “make-up” demand of 30 GPM.

7. Available voltage is 208/3/60.

8. There is sufficient area at the top floor to mount a drawdown tank if required.

9. There are no special services on site.

System Flow Capacity = __________ GPM

System Output Pressure = __________ PSI

System Header Size is _____________”


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CHAPTER 3: Pump Selection Considerations

SECTION I: PUMP TYPES

Pump Types Details

End Suction175 # W.P., Low first cost, good use of floor space, typically 400GPM or less, Low parts cost, relatively simple to repair, low tomedium pressure boosting.

Vertical In-Line175# W.P., Low first cost, excellent use of floor space, more costeffective on larger flows, reasonable parts cost, very simple torepair, low to medium pressure boosting.

Vertical Multi-Stage

250# W.P., Medium first cost, excellent use of floor space, morecost effective on smaller flows (100 GPM and less), reasonable tohigh parts cost, reasonably repairable, medium to high pressureboosting (80-200 PSI)

Vertical Turbine

250# W.P., High first cost, good use of floor space, more costeffective on very large flows and pressures, high parts cost,extensive repair work involved, medium to high pressure boostingat high flows. (50 + stories)

Note: W.P. stands for working pressure (i.e. suction pressure + boost)

SECTION II: OTHER CONSIDERATIONS

• 80% of all units will utilize End Suction Pumps.• Consider multiple configurations for the pump type available. (ex: 6500, 6600 or 6700

Series, DualPak, QuadPak, etc.)• Most systems should be considered to have an 18-20 year life cycle cost.• Consider location of unit. (ex: Outdoors require TEFC motors)


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CHAPTER 4: Drawdown Storage Tanks

SECTION I: APPLICATION

Tanks are to be used in systems that do not have a continuous water demand. (i.e. no make upwater or Air conditioning etc..)• Do Not assume that tanks will keep up with any appreciable service loads.

Tanks should not be sized according to booster size.• Tanks should be sized to store 20 - 30 Gallons of water (2 - 3 GPM leak loads)• The capacity of the tank is determined by the cut-in and cut-out pressure of the booster

system as well as the tank precharge pressure. (See Fig. # 8)• Tank pre-charge is determined based on the mounting location of the tank. (See Fig.’s # 9 -

12)

Tanks maintain pressure in piping system and supply small demands allowing pumps to be shutdown.• Based on 20-30 Gallons of useable storage, the system will achieve a minimum shutdown

of about 5 minutes based on a tank flow capacity of 2-3 GPM.

P PUMP STOP PRESSURE U psig 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125M 20 0.126 0.224 0.302 0.366 0.419 0.464 0.502 0.535 0.565 0.590 0.613 0.634 0.652P 25 0.112 0.201 0.274 0.335 0.386 0.430 0.469 0.502 0.531 0.557 0.581 0.602

30 0.101 0.183 0.251 0.309 0.359 0.402 0.439 0.472 0.502 0.528 0.552 0.573 0.593S 35 0.091 0.168 0.232 0.287 0.335 0.376 0.413 0.446 0.475 0.502 0.525 0.547 0.567 0.585 0.601T 40 0.084 0.155 0.215 0.268 0.314 0.354 0.390 0.422 0.451 0.478 0.501 0.523 0.543 0.561 0.578 0.594 0.608A 45 0.077 0.143 0.201 0.251 0.295 0.334 0.370 0.401 0.430 0.456 0.480 0.501 0.521 0.540 0.557 0.573R 50 0.072 0.134 0.188 0.236 0.279 0.317 0.351 0.382 0.410 0.436 0.459 0.481 0.501 0.520 0.537T 55 0.067 0.125 0.177 0.223 0.264 0.301 0.334 0.365 0.392 0.418 0.441 0.463 0.483 0.501

60 0.063 0.118 0.167 0.211 0.251 0.287 0.319 0.349 0.376 0.401 0.424 0.445 0.465P 65 0.059 0.111 0.158 0.201 0.239 0.273 0.305 0.334 0.361 0.386 0.408 0.429R 70 0.056 0.106 0.150 0.191 0.228 0.262 0.292 0.321 0.347 0.371 0.394E 75 0.053 0.100 0.143 0.182 0.218 0.251 0.281 0.308 0.334 0.358S 80 0.050 0.096 0.137 0.174 0.209 0.241 0.270 0.297 0.322S 85 0.048 0.091 0.131 0.167 0.200 0.231 0.260 0.286U 90 0.046 0.087 0.125 0.160 0.193 0.223 0.251R 95 0.044 0.084 0.120 0.154 0.186 0.215E 100 0.042 0.080 0.116 0.148 0.179

The chart above is a drawdown calculation chart. The numbers along the left side represent the call onpressure switch setting of the booster system. The top values represent the shut-off (shut-off = Pump shut-

off pressure plus maximum suction pressure - best case) The corresponding intersection between any cut-inand cut-out value will give you the actual storage when multiplied by the total tank capacity.


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Skid Mounted TankWhen the tank is mounted onto the system skid,it must be regulated separately. A Tank pipingconnection is required (see Fig. #12) which willconnect the “high” side of the pump to the tank.The connection will then “T” off to the dischargemanifold with a separate tank PRV. This PRV isset 2 PSI higher than the system designpressure in order to assure complete exhaustionof tank contents. In cases where the tank is skidmounted, you should allow for about double thefloor space required than for a remote mount oradjacent mount setup. Remember that the tankpressure will need to take into account SystemPressure plus pump shut-off pressure, so thiscould force the selection into a “code rated”storage tank.

Remote Mounted TankWhen a tank is mounted at the top of thesystem, it can be pre-charged to the systempressure AT THE LOCATION OF THE TANK.This means that, if the system is rated for a 30PSI residual pressure at the top of the building,the tank would only need to be charged at 28PSI (we deduct 2 PSI just to verify that the tankis not overcharged. In addition, there is no needfor a tank PRV since the tank is on the SYSTEMside which is REGULATED. In this case, we usethe friction loss in the piping system to chargethe tank. As the system begins to move towardshut-off, pressure increases in the piping due tothe lack of friction, it is this increase that willcharge the remote tank. Mounting the tank at thetop of the system lowers the tank pre-chargeallowing the use of a smaller or less costly non-code tank (if acceptable).


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Adjacent Mounted TankThis seems to be the most popular methodtoday of configuring the drawdown tank. Thetank is mounted somewhere at the same level ofthe system (usually directly next to it, nearlyalways in the same room.) The tank piping andPRV are still required, but the tank connection ismade in the field by the contractor rather than atthe factory. The System Pressure plus pumpshut-off must still be considered whenconsidering the pressure rating, but theadditional space required by the skid mountedtank can be partially avoided. Maneuverabilityand installation are also simplified. Pipingconnection is also mounted as in Fig. #12.Some advantages of this are that the systemskid size is much more manageable and smallversus the skid mount package.

SECTION II: PIPING CONFIGURATIONS

PRV’s

SuctionPressure

Water exits tankthrough same pipe

Tank PRV set @2- 5 PSI above P-1pump pressure.

Tank is fed fromhigh side of PRV’swith 1/2” coppertubing.

Check valveholds againstpressurebackflowthrough pumps.

Tank Piping Schematic (Adjacent and Skid Mounted Tanks)Tank feed line is piped into the “High” (pump) side of the Pressure Reducing Valves allowing full pumppressure plus suction pressure to enter the drawdown tank. When system is satisfied and pumps rise toshut-off, the thermal re-circulation line tells system to shut down. System “leak loads” are now providedfor by the pressure tank through the separate tank PRV which is mounted to the discharge manifold.

TIP: There is a drawdown calculator located at the far right tab of ArmCalc entitled “drawdown”. Input thetank size in the top left cell. (Graph results will change when you press “Enter”) Read across the top ofthe graph for the pump start pressure (this is the same as the system “on” pressure which the pumppackage is trying to maintain) On the left side of the graph read down for the pump stop pressure. (inthe case of an adjacent or skid mount tank, this is equal to the maximum possible suction plus pumpshut-off at zero flow; For remote tanks, use the start pressure as the tank pre-charge and the stoppressure as the piping friction loss calculation. This is typically 10% of Static Pressure)


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CHAPTER 5: Pump Staging for Energy Efficiency

SECTION I: APPLICATION

Consider alternate staging scenarios:• One of the benefits you enjoy with Armstrong is a wide choice of pump selections, system

configurations and staging scenarios. Make certain that you have exhausted all possiblecapacity splits. You may find that the total BHP used on an un-equal (33/67, 20/80,20/40/40, 10/45/45) split may be less than an equal (50/50, 65/65, 33/33/33, 50/50/50)pump capacity split

Don’t encourage consultants to “over-design” redundancy.• Redundancy is certainly reasonable to any design criteria, however there are ways to make

the best use of the pumping power and still have redundancy. (Ex: Suggest that instead ofusing a 65/65% capacity split which adds un-necessary capacity to the system when thelead pump runs, take the design load, add 15% redundancy and suggest a 33/67 splitwhere cost effective.) The redundancy is still built into the system, however the smallerpump will likely run most of the time.

SECTION II: PUMP SELECTION

Typical capacity splits and reasons for choice:

DuplexP-1 P-2 Possible reason for choice33% 67% Very economical (especially in system flows over 200 GPM), effective use of pumping

power, ability to use 3-Step sequencing control optimizing BHP to Flow need.

50% 50% Preferable in system capacities below 200 GPM since motor H.P.’s are typically thesame as 33/67 split, allows auto lead alternation (equal wear), parts interchangeable

65% 65% Similar to reasons used in 50/50 split, however, allows for additional redundancy since(1) pump operating alone can handle a larger portion of the load.

100% 100% Provides full stand-by in the event of a pump failure, recommended for packageswhich are typically very small in H.P. since this is not effective use of BHP.

TriplexP-1 P-2 P-3 Possible reason for choice20% 40% 40% Most common sequencing option, allows for up to 5-Step sequencing, very good

use of pumping power, small lead acts as jockey pump for large periods of low-flow.

30% 40% 40% Similar benefits to sequence above, however allows for up to 70% or 80% peakdemand with (2) pumps running but has 10% built in redundancy.

33% 33% 33% Typically used when minimum loads always exceed 20%, primarily used on hospitalapplications where loads are seldom low, this split only allows for 3-Step sequence.

30% 70% 70% Provides a peak load of 100% when (2) pumps are running as well as an increasedcapacity and 70% system redundancy, not used very often.

Example of System Splits and use of multiple sequences• In the following example of a 33/67% system split, a comparison is made on 50/50, 2 Step

sequencing versus 33/67, 3 Step. Notice how dramatic the savings are by simply changingthe existing system flow to sequence at un-equal capacities, as well as adding anadditional step of control to the pump package.


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SECTION III: THE BUILDING LOAD PROFILE

1 2 A M 4 8 N O O N 4 8 1 1

W A T E R D E M A N D % D E S IG N C A P A C IT Y

2 5 %

5 0 %

1 0 0 %

6 7 %

Typical residential building demand curve showing the relationship of system demandversus time of day. Notice how the system demand falls off in the early morning hours.

• System demand is ultimately determined by flow. When a building uses water, it is relateddirectly to the activities and usage habits of people and machines within the building. Sincewe size all systems to develop pressure, this demand has already been taken intoconsideration and the system is built to keep this pressure requirement at a constant “pulsefree” state. It only makes sense that, since pressure is constant and the flow varies(requiring additional pumping power), that the sequencing of pumps be directly related to ameasurable demand flow. Current sensing relays measure this “work” (GPM) exerted bythe motor through the pump impeller. In figure #13 we can see how this demand fluctuates.

• You are not required to use the flow splits as shown in the example. Sometimes it ispossible to optimize (i.e.: reduce horsepower consumption) by using a 20/80 split, forexample. Because we use current sensing relays and we have the option of determiningwhere the split is made, we can choose whichever split fits the application best.


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A Comparison of Energy Consumption for Varying Capacity Splits

*Note: The 33-67 Capacity Split reduces consumption by 29% and wastes 131% less power

Actual Consumption

33-67 Split

50-50 Split

Notice that by simply changing the flow split percentages, the pumps now follow the system demandmore accurately. This is how to optimize power consumption with constant speed pressure boosterpackages. The system becomes, in essence, a variable flow package, choosing the best motor (orcombination of motors) to run for a given GPM.

SECTION IV: SEQUENCING DEVICES

There are currently a multitude of choices for pump sequencing. The most popular of these areflow switches, pressure switches & current sensing relays. Below is a description of each andthe type of measurement each utilizes.

Amperage Hysterisis %

Syrelec

Flow Switch - senses water flowagainst a paddle which is in thewater stream. Paddle moves a “cam”within the body which actuates nextsequence. This is an accurate meansof measuring flow, however, can besubject to corrosion and obstruction.(Direct Measurement of Flow)

Pressure Switch - The pressure switchsenses a drop in pressure andactivates a device or relay. They areavailable in both single pointactuation and differential pressure.This mode of control relies primarilyon the pump curve characteristics asthey relate to pressure output.(Indirect Measurement of Flow)

Current Sensing Relay - The relaymonitors amperage draw created bythe motor as the flow increasesthrough the pump. This amperage isset to a specific “on” time based onengineer requested sequencing. It is anindirect measurement of flow, buthighly accurate. (Indirect Measurementof Flow via amperage)


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PROBLEM 2:

1. You are replacing a Duplex system which has a design flow of 200 GPM.2. The system was designed around a 65/65 split.3. The system pressure is based on a boost requirement of 50 PSI.4. Analyze the difference between 65/65 split vs. 33/67 with a 15% redundancy factor.

65%/65% 33%/67%

Pump #1: GPM ________ H.P. ________ vs. GPM ________ H.P. _________Pump #2: GPM ________ H.P. ________ vs. GPM ________ H.P. _________

Considerations• Flow Switch - is in contact with the pumped fluid, therefore, it is subject to corrosion or

obstruction. It can also fail mechanically. From a positive standpoint, the flow switch is adirect measurement of flow.

• Pressure Switch - is also in contact with the fluid and can be come clogged or fail dueto corrosion. It is an indirect measurement of flow since it measures the pressure outputof the pump as it relates to its curve. Suction pressures must be very accurate tofacilitate an accurate sequencing scenario.

• Current Sensors - read the motor amperage draw as the motor works to generate flowthrough the pump. Since this “work” is directly proportionate to the flow the currentsensor is measuring this in an indirect fashion, yet the amperage draw is veryrepeatable and highly accurate. Current sensors are not in contact with the pumpedfluid, nor do they have any moving parts. They are also able to sense voltage change.

A word about “non-overloading”…

Many engineers (through their association with HVAC systems) have become very careful aboutspecifying pumps which are non-overloading throughout their entire flow curve. If we look at thedesired sequence in a system, however, we would like to use as much of the motor as possiblebefore activating additional pumps in sequence.(see Section III of this chapter) This allows us toconserve power by “managing the flow load”. With a “flow based” measurement system, this caneasily be done, since the consultant can dictate (right down to the exact flow rate) where the nextpump will activate. Pressure switch based systems can be fooled by changes in suction pressure(which change the pump performance at any point on its curve) and therefore are unreliable for thispurpose. In a properly designed system utilizing FLOW based sequencing, the engineer can indicatethat…”the system shall be non-overloading throughout its entire SEQUENCE OF OPERATION”rather than the individual pump curve.


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CHAPTER 6:Variable Speed Pressure Booster Systems – Application and Design

There has been a lot of debate in the plumbing engineering community regarding the use ofvariable speed drives in domestic water pressure booster system applications. The debatecenters on energy savings and whether or not there is a reasonable payback for buildingowners on the additional first cost of a variable speed system. This paper will shed some lighton the issue, and perhaps provide design engineers with some tools to better understand whenvariable frequency drives (VFD’s) make sense.

The purpose of applying VFD’s in a pressure booster system is to allow constant pressureregulation without the need for pressure reducing valves. There are four key elements toconsider in the application of VFD’s. The first has to do with the nature of the plumbing system,the second with the sequencing, the third with selection of pumps and hydraulic efficiency, andthe fourth with the nature of the end user’s electrical service provider.

SECTION I: THE PLUMBING SYSTEM

A pressure booster is designed to account for five fundamental variables in any system:1. Flow. The pressure booster must provide adequate flow under a wide range of demand

conditions.2. Residual Pressure. This is the minimum pressure required at the most remote fixture in the

plumbing system.3. Static Height. This is the elevation of the most remote fixture above the incoming supply

main.4. Supply Pressure. The worst case pressure on the supply side from the municipality must be

considered in calculations. This pressure should be taken after the water meter and back-flow prevention device. These devices can reduce the incoming supply pressure by as muchas 15psi.

5. Losses. The friction loss calculation should include losses within the pressure boostersystem itself (typically about 5psi).

Figure 1: The boost pressure is denoted by B and the variable pressures are denoted by V in the aboveillustration. The gray area is the opportunity for energy savings running a pump at variablespeed in a domestic water boosting application.

Residual Pressure

PRV Losses

Static Pressure

Friction Loss

Suction Pressure

B

V

Supply + Boost = System Pressure


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In analyzing the practicality of using VFD’s, we must now consider which variations of the aboveparameters yield energy savings when varying the speed of the booster pumps. Of the abovefive factors, static height and residual pressure generally do not change. As such they will havelittle or no impact and hence will yield no opportunity to vary the speed of the pumps.

Variations in flow yield an opportunity for speed reduction since flow variations cause the pumpto operate at different points on the pump curve. If the pump curve is steep, the opportunities forspeed reduction and energy savings increase.

Perhaps the greatest opportunity for energy savings is in the varying supply pressure. In somemunicipalities, this pressure can vary as much as 50psi due to daily peak demands or seasonalconsiderations such as irrigation in the summer.

Finally, losses can potentially yield energy savings, as they are negligible at low flows. Theadditional pressure supplied for losses can be compensated for if the pressure sensor for thesystem is located remotely in the plumbing system.

You will note that a constant speed pump will operate along the characteristic pumpperformance curve (upper curve) with the PRV limiting the pressure to the desired constantdischarge pressure. The variable speed pump will operate along the system curve (lower curve)by varying the speed of the motor driver.

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140 160 180 200Flow

PSI

3500 rpm Constant1950 rpm ConstantVFD Control Curve

Design Point

Figure 2: Once again, the boost pressure is denoted by B and the variable pressures are denoted by V inthe above single pump performance curve. The gray area is the opportunity for energy savingsrunning a pump at variable speed.

Of the above factors, the variable pressure parameters are quite easily calculated; however,flow adds a dimension of complexity to the overall analysis. This is due to the measure ofuncertainty in building demand or load profile of the system. To be precise, we would be able toexactly calculate the energy savings yielded by a variable speed system using the followingformula (allowing the ∆t time increment approach zero):

E = (ΣQP∆t/η)constant speed - (ΣQP∆t/η)variable speed

VB


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Clearly, there are a number of uncertain parameters in this formula. It is useful for analysispurposes to make assumptions to yield a quicker estimate of potential energy savings in thesystem. For illustration purposes, we will look at a single pump and system resistance curve tobetter understand the analysis of such a system. Further, for the purposes of simplicity, we needto make some assumptions before we begin our analysis.1. Load Profile (Q). This can be estimated in as much detail as desired. For the purposes of

this article, we will look at an average building load assuming 50% of design flow for a singlepump designed for 200gpm. The same analysis can be done using multiple pumps, multipletime increments, and average loads during those time increments to increase the accuracyof our results.

2. Efficiency (η). Both pump and motor efficiencies at the average demand are assumed to be65% and 85% respectively.

3. Variable Pressure (∆P). We will assume the variable pressure to be daily rather thanseasonal. Seasonal variations will yield reduced savings since the high pressure is onlyexperienced during a given period of the year. For the analysis, we will assume a boostpressure of 80psi with 10psi of losses, 10psi of supply pressure variation, and 10psipressure rise to shutoff based on the pump curve. Thus, the total ∆P will be 30psi from zeroflow to the design 200gpm.

In addition to the above assumptions, we will approximate the variations in pressure across theoperating conditions as being linear. At 100gpm, we can then assume the pump head to be85psi, and the suction variation and friction losses to be 5psi each. As a further assumption, wemust assume some loss in the drive itself. For the purpose of simplicity, we will approximate thisat 3%.

The above assumptions yield the following daily energy savings for the pump considered:

E = (QP∆t/η)constant speed - (QP∆t/η)variable speed

E = [(100gpm)(85psi)(2.31)(24hrs)/(85%)(65%)(3960)]- [(100gpm)(70psi)(2.31)(24hrs)/(85%)(65%)(97%)(3960)]

A savings of 32.5kWhrs per day is realized. At $0.10/kWhr, the daily savings for a buildingowner would be $3.25 yielding an annual energy savings of $1,186.25.

SECTION II: SEQUENCING CONSIDERATIONSThe above analysis simply considers the operating conditions in the plumbing system andneglects one key feature of pressure boosters: pump sequencing or staging. The controls anddata available when using VFD’s can yield additional energy savings if applied intelligently.

The key consideration in sequencing is maximizing pump efficiency. When VFD’s are appliedand pumps are sequenced based on a single parameter such as speed (as in the case of asystem with a single variable speed pump and constant speed lag pumps), pumps operateanywhere on the curve with no opportunity for maximization of pump efficiency. The same istrue of pressure, flow, or kW sequencing. Monitoring multiple parameters allows pumps to besequenced based on the location on the pump curve. In this case pump efficiency can bemaximized yielding additional savings. You will note that operating the same pump at 75%efficiency rather than 65% yields 15% in energy savings.


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Best Operating Algorithms and the Need for Equally Sized PumpsIn conventional, constant speed systems, it is common for a small lead “jockey pump” to beapplied to operated during off-peak hours. This works well on constant speed systems, butpresents a few problems in a variable speed system.

Unequal pumps perform hydraulically differently due to their different characteristic performancecurve. If pumps are sized unequally, there are two choices one can make on the proportional,integral, derivative (PID) pressure control:

a) Independent PID for unequal pumpsThis is inherently unstable and generally is not used. The instability is due to the PID for onedrive working against the PID in the other. One drive speeds up while the other slows down- this is a cyclic effect and is difficult to control without dramatically reducing the systemresponse time. The damping required in the PID leads to fluctuation in pressure actualpressure vs. the set point pressure.

b) Single PID for all pumpsIf the pumps are not equal and operating at the same speed, the pumps will operate on thecurve at the point of intersection of the two pump curves. This is equivalent to a constantspeed system operation and does not gain any energy savings other than that available inthe PID (pressure regulation). What happens is that since the smaller pump has a steepercurve with higher shutoff head, when two pumps are running, the smaller pump runs at theend of it's curve (inefficient point) and the larger pump runs near shutoff to the left on thecurve (another inefficient point).

The above choices are further complicated by the problem of when to sequence pumps on andoff. The decision to sequence pumps requires flow, differential pressure, and speed inputs witha complex algorithm to sequence optimally. This has not been demonstrated to work properly inapplication.

Any sequencing algorithm based on single inputs such as pressure, speed, flow, or powerconsumption is flying blind – there is no way for the pump controller to know how efficiently thepumps are operating and what combination of pumps is the best choice. By sizing pumpsequally, PID stability is easily achieved – the equal pumps perform at the same location on thepump curve. Combining this with a best operating point (BOP) sequencing algorithm,sequencing of pumps based on a location on the pump curve regardless of speed, pressure,and other system-related factors is possible. Clearly, there is a great opportunity for energysavings based best hydraulic performance considerations. This design principle also makes asystem easily adjustable in the field under varying operating conditions.

SECTION III: PUMP SELECTIONBy convention, pumps are selected so that the design operating point is to the left of the bestefficiency point (BEP). Let’s examine why.

Traditionally, pumps have been sized with additional pump head to ensure the needs of thesystem are met. In a traditional constant speed pressure-sequenced system, the second pumpwould be sequenced on (turned on) when the first pump begins to run to the right of the designpoint on the pump curve. This is due to the excess head in the initial calculations. Since therewas no way to account for this pump head in application other than throttling of the pump,design yielded pumps which operate and are sequenced to the right of the best efficiency point.


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0

10

20

30

40

50

60

0 20 40 60 80 100 120 140 160 180 200Flow

PSI

TraditionalDesign Point

Best DesignPoint

BestEfficiency

Point (BEP)

Figure 3: Traditional pump selection does not apply in variable speed pressure boosting if best operatingpoint sequencing is applied. Designing to the right of the best efficiency point maximizessystem hydraulic efficiency.

If this same assumptions are applied in a flow-based (current, kW, or flow) or best operatingpoint sequenced system, pumps never operated to the right of the design point. In fact,additional pumps are sequenced on just when the pump begins to perform efficiently. Thismeans that the system runs more pumps than necessary, and that the pumps are operating atless efficient locations on the pump curve.

With the above knowledge, it is clear that pumps in a flow-based or best operating pointsequenced system should be selected to the right of the BEP. This strategy yields additionalsavings in two ways. The first is that the system will leave a single pump operating when it isclose to its BEP maximizing pump efficiency. The second is that selection further to the right onthe pump curve yields additional pump shutoff head. This increased shutoff head increases the“gray area” in the illustrations. The steeper rise to shutoff yields greater speed reductions at lowflows, and consequently additional energy savings.

SECTION IV: ELECTRIC UTILITIES AND BILLING POLICIESThe final consideration in the application of VFD’s applies for any piece of mechanicalequipment that uses an electric motor. Intuition and rudimentary economic theory support amodel in which a commodity or service is bought and sold based on an agreed upon price. Thetotal amount paid is proportional to the net amount of commodity or service provided. One appleis $1. Ten apples are $10. In a free market, the price will fluctuate based on the availability(supply) and the need (demand) for the commodity or service. The principle is very intuitive.

The problem with the above model is that the bandwidth of the transaction or “delivery pipeline”is assumed to be infinite. If we apply a capacity constraint to the pipeline, the theory of supplyand demand breaks down. Plenty of a particular commodity may be available, but the demandmay remain unmet.


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Electric utilities have the pipeline problem. A customer’s demand for increased bandwidth hurtsthe electric utility in two ways: it must increase the size of the pipeline (upgrade the distributiongrid), and must produce more power to cover the higher theoretical peaks based on theincreased bandwidth of the distribution grid. In theory, unused bandwidth is unusable to theutility. Further, unused bandwidth demands that the utility have enough power to handle therelatively rare case when the full capacity of the pipeline is needed.

Electric utilities around the world use various strategies to deal with this very scenario. Onemeans of managing the pipeline problem is to charge customers not for the amount of productused, but for the size of the pipeline required to deliver peak power to the customer.

This has significant implications for application of electric motors. The starting current requiredto start a motor turning can be as high as 10 times the actual operational full load amps. It is thispeak that the end user will pay for. By reducing the starting current, therefore, one can yieldenormous savings for an end user. VFD’s accomplish this task by soft-starting and soft-stoppingmotors. Inrush amps are drastically reduced, and in cases where the utility charges “pipelinepenalties”, energy bills for the entire building can be cut by as much as half by applying VFD’s.

ConclusionIn closing, it is useful to consider some general rules for application of VFD pressure boostersystems. Some prime examples for application of VFD’s in pressure boosters are as follows:1. Buildings with long runs of piping such as schools and hospitals2. Buildings with undersized piping such as older apartment buildings3. Buildings requiring 10hp or larger pumps (larger motors yield greater savings when using

VFD’s)4. Neighborhoods with varying supply pressures.5. Where the electric utility charges for daily or hourly peak power rather than for cumulative

power consumption.

Further to energy considerations, VFD’s may be applied to solve other problems in a systemsuch as water hammer or excessive maintenance of pressure reducing valves. Otherconsiderations aside, the key factors to consider are variable pressure in the system, loadprofile, pump selection, and sequencing strategy. Variable speed systems will save energy inany application. Achieving a reasonable payback time for building owners is the keyconsideration. When these factors are considered, the payback can be significant.


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CHAPTER 7: Control Panels

SECTION I: OVERVIEW

Controls• The controls for Armstrong Booster Systems consist of an electric circuit which operates

the starters of the motors. The panel is supplied by the same power source as the boostermotors. The controls are housed in a NEMA rated enclosure and are composed of a seriesof monitoring, control, and logic components.

• Understanding the circuit schematic can make life much easier in the field when starting up,fine-tuning, and maintaining a booster system. Often, problems which arise in the operationor start up of a booster system are linked to the controls even though the problems mayseem to be with the motors and pumps, or the piping and valves of the system.

Safety• Because of the high voltages required by the motors, safety cannot be emphasized enough

in making adjustments to the controls.• The Bad News: Some of the wires inside the panel are live, even when the panel door is

open. Always consult the instructions on the inside of the panel door or this manual if youare unsure of the proper safety procedures.

• The Good News: The circuits will not store latent charge when the panel power is off sincethere are no capacitors in any of the circuits. Result: No nasty shocks from residualcharges stored in the circuits.


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Schematics• Schematics for electric circuits can be confusing. With this in mind, this handbook was

composed to remove the guesswork by using block diagrams to explain the schematicsymbols.

• Two important terms need to be understood at this point. Electricians use the terms “open”and “closed” circuit. OPEN means there is a break in the circuit preventing current flow.CLOSED means the circuit is continuous and unbroken allowing current flow.

• These definitions lead to a basic rule:

OPEN = OFF (no current flow/cold wire) CLOSED = ON (current flow/hot wire)

• Components of circuits such as switches and relays are often spoken of in relation to these

terms. A Normally Open component in its usual state breaks a circuit preventing currentflow. A Normally Closed component in its usual state keeps a circuit continuous allowingcurrent to flow. Schematic symbols for a component indicate whether it is normally open ornormally closed.

Note: The normal state refers to the position of the component (either open orclosed) as that component would be in the DE-ENERGIZED, DE-PRESSURIZED state.To clarify, all pressure switches appear as they would with zero pressure, and motoroverloads appear as open (even though during normal operation, these componentsare closed!).

• Another important element of the schematic is the list of reference numbers printed

vertically on the left hand side of the diagram. These numbers are location references forcontactor and relay coils. You will see that to the right of each contactor and relay coil is alist of numbers in brackets. These numbers give the location of the switches actuated bythe coils on the diagram. These are not to be confused with terminal numbers whicheither appear as labels on arrows or are enclosed in boxes on the schematic.

• To locate the switch actuated by the coil:a) Read the numbers to the right of the coil.b) Go to the corresponding numbers on the left side of the schematic.c) Search the schematic to the right of the reference number horizontally until the

switch is located.


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• Lastly, please note that all schematics shown in this handbook are for a three phaseDuplex Booster System. These provide examples you can adapt as required when readingschematics in the field.

The Basic Control Panel CircuitEvery control panel for Armstrong Booster Systems can be broken down to the followingcomponents plus the additional options selected by the customer:

a) Main Disconnect and Motor Protector Circuitsb) Power Transformers and Panel Protection Circuitsc) Pump Selection and Shunting Circuitsd) Current Sensing and Control Relayse) Pump Protection Circuits and Alarms

G ro u n d

M A IN D IS C O N N E C TA N D M O T O R

P R O T E C T O R C IR C U E T S

P O W E R T R A N S F O R M E R A N DP A N E L P R O T E C T IO N

P U M P S E L E C T IO N A N DS H U N T IN G C IR C U IT S

C U R R E N T S E N S IN GA N D C O N T R O L R E L A Y S

P U M P P R O T E C T IO NA N D A L A R M S

C O N T R O L /L O W V O L T A G E S ID E M O T O R /H IG H V O L T A G E S ID E

Block Diagram of Complete Control Circuit


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The block diagram on the previous page depicts this schematic. As each component isdiscussed, refer back to this schematic to identify where each element is located.


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SECTION II: MAIN DISCONNECT and MOTOR PROTECTOR CIRCUITS

TRANSFORMER

SHORT CIRCUIT PROTECTOR

OVERLOADPROTECTOR

Motor &Pump System

MAIN DISCONNECTSWITCH

POWER

Control Panel

Block Diagram of Main Disconnect and Motor Protector Circuits

Main Disconnect Switch• The main disconnect is the main power switch for the entire booster system.• All Panel and Motor servicing should be performed with the main disconnect in the

OFF position. Setting the HAND-OFF-AUTO (H-O-A) switches to the OFF positiondoes not disconnect power from the controls.

• The main disconnect switch releases the control panel, motors, and pumps from the powersupply. As a safety feature, the panel door cannot be opened without first switching to theopen (OFF) position.

• The main disconnect dial/switch is located at the top right hand corner of the panel.• Warning: Though the open panel is not live, the wires entering the panel to the

disconnect at the top of the panel are LIVE. DO NOT TOUCH.

Schematic of Disconnect Switch. The location of the switch on the panel is indicated by the arrow.


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Motor Protector CircuitsEvery panel houses a protection circuit for the motors. These circuits consist of two basiccomponents:

a) Short Circuit Protector: This is a quick-trip breaker which protects the motor frompotentially damaging current surges. Typically, the short circuit protector will trip on 13times the full load amps of the motor (maximum motor current rating).

b) Overload Protector: This bi-metal trip device is heat sensitive and will trip if the current tothe motor exceeds the motor current rating for more than a given period of time.

The short circuit protector (left) and overload protector (middle) combine to form a completemotor protector circuit (right). Within the controller, these components are integrated into a singlecomponent called an overload relay. The device has a setting for the maximum allowable amperage, anda two push button circuit breaker (pushing in the red button opens the circuit / pushing in the white buttoncloses the circuit).

• These circuits are separated from the actual motor starter by a set of contacts which turnindividual pumps on and off as required by the flow demand conditions. The logic for pumpswitching is contained in the pump shunting circuit and relays discussed in Sections IV andV. A schematic showing the main disconnect and motor protection circuits is shown below.

Main Disconnect and Motor Protection Circuit. Note that the lower segment of thediagram (marked “P1” and “P2”) represents the motors and their respective starters.


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SECTION III: POWER TRANSFORMERS and PANEL PROTECTION CIRCUITS

C O N T R O LT R A N S F O R M E R

C o n t r o l P a n e lC i r c u i t

C O N R O LC I R C U I T

B R E A K E R

P O W E RO N

Block Diagram of Power Transformer and Panel Protection Circuit

Control Transformers• The control transformer separates the motor side (high voltage) from the control side (low

voltage) of the booster system.• The control transformer steps down the voltage to the control panel. Though the motor may

use three phase 208V to 600V power, the control portion of the panel always runs on singlephase 115V power. The transformer takes care of this voltage conversion.

Control Transformer. The left side is the low voltage side providing power to the panel.

The right side is the high voltage supply which powers the motors.

Control Circuit Breakers• A control circuit breaker protects the more sensitive components (relays and contacts) from

being damaged by current surges.• This standard circuit breaker trips at 0.5 amps to 3.0 amps depending on the system’s

combined horsepower.

The control circuit breaker prevents current overloads in the controls' sensitive components.


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Power On Pilot Light• A pilot light indicates that power is being supplied to the controls. Provided that the control

circuit breaker is closed, this pilot should be lit.

The Power On pilot light informs the controls operator that the panel is live.

• We now are able to discuss the fundemental panel protection and motor protection circuits.On the schematic, the main power source is supplied at the right of the disconnect switch.This power supplies the motors via the motor protector circuit and is stepped down to thepanel voltage via the transformer. This is the junction that separates the high voltage(motor) side from the low voltage (control) side of the control panel.

• The control circuit breaker then protects the controls from current surges. All things beingnormal, the panel is supplied with power lighting the Power On pilot light. This circuit can beseen below.

Control Protection, Transformer and Motor Protector Circuits. The portion of theschematic on the left side of the dashed line was discussed in this section.


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SECTION IV: PUMP SELECTION and SHUNTING CIRCUITS

F r o m P r e s s u r e S w itc h

A L T E R N A T O RS W IT C H

P U M P

S H U N T IN G

C IR C U IT

H -O -A

S T A R T E R # 2H -O -A

S T A R T E R # 1

L A M P

L A M P

Block Diagram of Pump Selection and Shunting Circuits

Manual Alternator Switches• Manual alternator switches are standard for 50-50 capacity split Duplex systems and for the

two lag pumps in the Triplex systems. The switch allows selection of which pump is thelead pump. This allows the operator of the system to equalize wear on the motors andpumps by periodically changing the alternator setting.

• The switch is a standard selector switch (marked either “P1-P2” or “P2-P3”) located at thebottom center of the panel.

Manual alternator switch determines which pump leads.

Automatic Alternator Switches• Automatic alternator switches are optional on units requiring alternation of the lead or lag

pumps. The switch serves the same purpose as the manual selector switch.• The switch is designed to alternate on every no-flow condition and on shutoff of one pump

after a full flow condition.


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Pump Shunting Circuits• The shunting circuit controls the turn-on and shut-off of pumps in the Duplex and Triplex

booster systems. This circuit contains the logic which sequences the booster system.• The shunting circuit is governed by the readings of one or more current sensing relays (see

Section V on current sensing relays). The current sensing relay causes control relays toopen and close contacts in this circuit. This action starts and stops the motors in responseto the flow demand.

• The circuit is only activated when all the pumps of the booster system are set to the AUTOposition on their respective H-O-A switches.

Pump Shunting Circuit holds key to pump sequencing. The circuit is

only activated when the pumps are placed in the AUTO position.

Pump Run Indicators and Motor Contactors• Pump run indicator lamps (Pilot Lights) are placed in parallel with the contactor coil for each

motor. The contactor coil actuates a contact located between the motor protector circuitand the motor to close. The closed contact supplies power to the motor and starts thepump running.

• This connection also lights the pump run lamp on the panel allowing the operator to knowthe status of each pump of the system.

Pump run indicator and contact coil in parallel. The coil closes contacts starting a motor.


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SECTION V: CURRENT SENSING and CONTROL RELAYS

SHUNTINGCIRCUIT

CURRENTSENSING

RELAY

CONTACT #1

CONTACT #2

CONTROLRELAY #2

RUN PERIOD TIMER

CONTROLRELAY #1

Current Sensing and Control Relays

Current Sensing Transformers• One leg of each motor lead is passed through a current transformer coil. These coils

measure the current drawn by each motor, indirectly measuring the GPM flow through eachpump.

• The current sensing relays supplied by the current transformers are factory set to an upperand lower current threshold. When the current exceeds the upper threshold, an additionalpump is turned on to cope with the increased flow. Likewise, when the current drops belowthe lower threshold, a pump is shut down to conserve energy.

• The upper threshold controls the turn-on of the next pump and is adjusted by the dialmarked “Threshold” on the current sensing relay.

• The lower threshold controls the shut-off of a running pump. It is set as a percentage of theupper threshold using the dial marked “Hysteresis” on the current sensing relay.

Current Sensing Relay. In combination with a control relay, the CSR activates a current transformer

in the starter (part of the contact arrangement) to start the motor. The numbers 19 and 20 marking thearrows indicate a connection to the matching numbers on the motor lead.


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TIP: The number of current sensing relays in a system can be determined by the formula:

DUPLEX: ONE RELAY + ONE RELAY PER STEP OF SEQUENCINGTRIPLEX: TWO RELAYS + ONE RELAY PER STEP OF SEQUENCING

EXAMPLE: A Duplex System on 33-67 capacity split supplies a peak demand of300GPM. The system is designed for conventional sequencing (i.e. The leadpump runs constantly. The lag pump turns on and off as the flow demandrequires). The motors are 5 and 10 hp and run on a 208V supply voltage. Atfull flow, the lead pump draws 50 amps.

The system has one current sensing relay. The current sensing relay turn-onthreshold would be set to 50 amps. This would cause the lag pump to turn onwhen the lead pump draws 50 amps.

The shutoff threshold would be set to about 60 amps. This would cause thelag pump to shut off when both motors together draw 60 amps. The“Hysteresis” setting would be 20%. Reason: 20% of 50 amps is 10 amps.Fifty amps (upper threshold) plus 10 amps gives a shutoff threshold of 60amps.

Why is the shutoff threshold set higher than the turn-on threshold? This isbecause two motors working at the same flow rate as one motor alone willdraw more amps.

Current Sensing Relay Switches• Every time a current sensing relay coil reads a threshold current, it actuates a current

sensing relay switch to either open or closed (depending on whether the switch is normallyopen or normally closed).

Current sensing relay switch closes actuating a control relay to start or shut down a motor.

• As the relay coil requires, this relay switch will open or close causing one of the following tohappen:

a) The switch closes causing a control relay to turn on a pump..b) The switch opens starting the countdown on the minimum run timer. When

the timer runs down, a control relay turns the pump off.

CURRENTSENSINGRELAYCOIL

CONTROLRELAYCOIL

MOTORCONTACT


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Control Relays• A control relay coil is actuated by the closing of a current sensing relay switch.• The control relay in turn actuates a contact to close starting a motor.• This coil, once activated will not deactivate with the opening of the current sensing relay

switch. Instead, a minimum run timer holds the circuit closed until the timer has run down.• This feature prevents cycling of pumps during near-threshold flow conditions.

Control Relay Coil actuates the motor starter contacts inside the shunting circuit.

Contacts• A contact corresponding to each control relay is located in the pump shunting circuit. The

contact reacts to the coil in turn actuating the motor contactors and will do one of thefollowing:

a) Turn on a new pump and shut the running pump off.b) Turn on a new pump and leave the running pump on.c) Shut off the running pump after the set time.

Contacts (RP2) close to start the motor running or open to shut one down.This action opens or closes the motor contactors (C1).


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Minimum Run Timer• A minimum run timer for each current sensing relay ensures that pumps do not cycle

damaging the motors.• The timer is started when the current sensing relay opens. The timer keeps the control

relay energized and the corresponding contact closed. The result is that instead of thepump corresponding to the control relay turning off, the pump keeps running for thedesignated time period. After this time, the connection is opened and the pump turns off.

• For example, if the timer is set for 5 minutes, and a pump is turned on, it will stay on for atleast five minutes. Cycling of the pump can only occur at five minute intervals preventingcycling damage to the motor and pump.

Timing Relay holds the contact for a set period of time in order t o prevent pump cycling.


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SECTION VI: PUMP PROTECTION

CircuitBreaker

PRESSURESWITCH

SOLENOIDVALVE

AQUASTAT

Transformer

PUMPSYSTEM

Block Diagram of Pump Protection Circuit

Low Suction Pressure Warning• A pressure switch protects the pumps from the effects of low suction pressure. If the

suction pressure feeding the system drops below a minimum threshold the low suctionpressure switch will open, shutting all pumps down.

• The minimum suction pressure cut-out is factory set to 5 psi but may be adjusted, thoughthis is strongly advised against.

• The low suction switch will turn all pumps off and light the low suction lamp warning.• The pressure switch has two settings:

a) Cut-out value: This opens the contacts shutting down the pumps (set at 5 psi). Onthe switch itself, this setting is adjusted by turning the top screw. The actual settingis read on the scale on the side of the switch.

b) Cut-in value: This is adjusted relative to the cut-in value using the “Differential”setting. (Cut-out value + Differential Setting = Cut-in Value) The differential is setafter the cut-out value has been set, and should be set to its minimum to beginadjustments. After the cut-out has been set, turn the bottom screw to the lettercorresponding to the desired differential. (Factory set to 5 psi above the cut-outpressure.)

• Warning: If the low suction pressure switch is set too close to the minimum NPSH,

pump cycling will occur. If the situation is not corrected, damage to the motorstarters can be expected. The same problem will occur if the “Differential” setting istoo low.


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Fig.# 21: Low suction pressure switch shuts down system and warns by lighting pilot.

High and Low System Pressure Warnings• Two further pressure switches with warning pilots are available as options (see Section VII

of this chapter).• These switches are also factory set and can be complimented by corresponding low and

high system pressure warning lamps. Aquastats and Solenoid Valves• During normal operation, a steady flow of water through the pumps carries away the waste

heat they generate. Because of this, high temperatures are occasionally generated duringperiods of low flow. High temperature water can affect the performance of and evendamage the pumps.

• An aquastat is available as an option and is installed on the suction header to measure thetemperature of the water in booster system.

• The aquastat is set for a certain temperature (120°F) at which it actuates a solenoid valvelocated on the side of the control panel. This valve opens bleeding the potentially harmfulhot water.

• In No-Flow Shutdown Systems (Option X), the aquastat is used to trigger a pressure switchwhich shuts down the system. In this case, no solenoid valve is required since the aquastatis set to a much lower temperature (90°F).

Aquastat and Solenoid valve act together to bleed high temperature water from the pumps.On No-Flow shutdown systems, the solenoid valve is not necessary since

the pumps shut down long before high temperatures are generated.


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SECTION VII: OPTIONS

No-Flow Shut-down• No-Flow Shut-down (Option X) is an energy saver option, and requires a drawdown tank.• Though this incurs an initial cost, on systems where no flow conditions occur for several

hours a day (i.e. office buildings, etc.), the energy savings can be dramatic. Typically, theoption pays for itself within the first two years of operation.

• The No-Flow Shut-down option uses an aquastat to trigger the shutdown. The aquastat isset from its usual 120°F to 90°F. This typically shuts the system down after about threeminutes of a no demand condition. No solenoid bleed valve is required since the systemshuts down well below the usual 120°F threshold.

• The aquastat may need resetting depending on the ambient water temperature of theparticular location. Check the troubleshooting guide or instructional video beforeresetting the aquastat.

• The drawdown tank maintains system pressure and handles leak loads while the pumpsare not running. A “call on” pressure switch triggers the lead pump to turn on when ademand is placed on the system.

Enclosures• Though the NEMA 1 Enclosure is Standard for Armstrong Booster Systems, a wide range

of indoor and outdoor enclosures of varying protection ratings are available as options.• Be sure the enclosure suits the needs of the customer by refering to the listing of NEMA,

CSA, and UL standard codes for control panel enclosures on page 40 of this handbook.

AlarmsA variety of alarm options are available. All are visible warning lamps and may be complimentedas required by Option H, the audible alarm buzzer (linked in parallel) with the standard alarmlamp. The following alarms are offered:

a) High System Pressure: This option (Option K) is simply a pressure switch with indicatorlamp on a bypass circuit much like the low suction pressure alarm. This alarm isaccompanied by a system shutoff and a manual reset button on the panel door.

b) Low System Pressure: Two different low system pressure alarms are available. Besure to quote the correct option on orders. Option AD will shutdown on the lowsystem pressure condition. Option Q will turn on another pump to compensate for thelow pressure. This pump will remain engaged until the reset button is pushed. Bothoptions have manual resets.

c) High Suction Pressure: Option G is also a bypass type pressure switch which will shutthe system down on high suction pressure readings. This option has automatic resetwhen the suction pressure drops below the set threshold pressure.

d) Low Suction Level Shutdown: Option AEe) Motor Overload Lamps: Option D is mounted on the motors themselves. The lamps will

light if the motor current level exceeds the set overload current.

Automatic Alternation• Automatic pump alternation (Option I) is available on a 24 hour/7 day per week time clock,

or automatically after every full demand and no-flow condition.• Instructions for programming the timer are included inside the panel door with every order

on this option. The timer controls a relay which toggles the pump alternation switch at thetime set on the clock (daily or weekly).


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HydroSaver Sequencing• The HydroSaver Sequencing options (Option S, T, and U) require the addition of an extra

control relay per stage of sequencing. Though there is a cost for this option, this cost isoften offset within the first two years of operation in energy savings.

• Option S adds three step sequencing to a Duplex system typically using a 33-67 capacitysplit between the two pumps. The arrangement leads to the following pump run conditionsdepending on the demand flow:

− Step 1: Pump 1 running, Pump 2 off (33% capacity)− Step 2: Pump 1 off, Pump2 running (67% capacity)− Step 3: Pump 1 and Pump 2 Running (full capacity)

• Option T adds four step sequencing to a Triplex system using a 20-40-40 capacity splitbetween the three pumps. The arrangement yields the following pump configurationssubject to demand conditions:

− Step 1: Pump 1 running, Pumps 2 and 3 off (20% capacity)− Step 2: Pump 2 running, Pumps 1 and 3 off (40% capacity)− Step 3: Pumps 2 and 3 running, Pump 1 off (80% capacity)− Step 4: Pumps 1, 2, and 3 running (full capacity)

• Option U takes full advantage of the Triplex 20-40-40 capacity split by breaking thesupplied flow into five steps:

− Step 1: Pump 1 running, Pumps 2 and 3 off (20% capacity)− Step 2: Pump 2 running, Pumps 1 and 3 off (40% capacity)− Step 3: Pumps 1 and 2 running, Pump 3 off (60% capacity)− Step 4: Pumps 2 and 3 running, Pump 1 off (80% capacity)− Step 5: Pumps 1, 2, and 3 running (full capacity)


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NEMA 1General Purpose - IndoorIntended for indoor use. Providesprotection from accidental contact ofpersonnel with enclosed equipment.Standard Armstrong enclosure.

NEMA 2Dripproof - IndoorIntended for indoor use. Protectsequipment from falling dirt and fallingnon-corrosive liquids.

NEMA 3Dust, Rain, and Sleet resistant -OutdoorIntended for outdoor use. Protectsenclosed equipment from wind-blowndust and water. Limited resistance tosnow, sleet, and ice. (NOT SLEETPROOF)

NEMA 3RRainproof / Sleet-resistant - OutdoorSame as NEMA 3 with addedresistance to rain and snow.

NEMA 4Water/Dust-tight - Indoor/OutdoorIntended for indoor/outdoor service.Protects equipment from splashing,seeping, falling, or hose-directedwater and from severe externalcondensation. Limited resistance tosnow, sleet, and ice.

NEMA 4XWater/Dust-tight - Indoor/OutdoorCorrosion ResistantSame provisions as NEMA 4 with theaddition of resistance to corrosion.

NEMA 12Indoor Industrial - Dust and Drip-tightIntended for indoor use. Protectsequipment from fibers, flyings, lint,dust and dirt, and light splashing,seepage, dripping and externalcondensation of noncorrosive liquids.

NEMA 13Indoor Industrial -Dust and Drip-tightIntended for housing pilot devicessuch as limit switches, foot switches,pushbuttons, selector switches, pilotlights, etc. and to protect thesedevices from lint and dust, seepage,external condensation, and sprayingof water, oil or coolant.

CSA 1IndoorGeneral purpose enclosure providingprotection from accidental contact ofpersonnel with enclosed equipment.

CSA 2Drip Resistant - IndoorEnclosure constructed to provide adegree of protection from dripping andlight splashing of non-corrosive liquidsand falling dirt.

CSA 3Rain-resistant - Indoor/OutdoorIndoor/Outdoor enclosure constructedto provide a degree of protection fromrain, snow, and windblown dust.Undamaged by external ice formation.

CSA 3RRainproof - Indoor/OutdoorSame as CSA 3 with higher resistanceto rain and snow. Also undamaged byexternal ice formation.

CSA 4Rainproof - Indoor/OutdoorIndoor/Outdoor enclosure constructedto provide a degree of protection fromrain, snow, windblown dust, splashingand hose-directed water. Alsoundamaged by external ice formation.

CSA 4XCorrosion-resistant - Indoor/OutdoorSame as CSA 4 enclosure with addedresistance to corrosion.

CSA 12Indoor IndustrialConstructed so as to provide a degreeof protection from circulating dust, lintfibers, and flyings; dripping and lightsplashing of noncorosive liquids; notprovided with knockouts.

CSA 13Indoor IndustrtialConstructed so as to provide a degreeof protection against circulating dust, lintfibers, and flyings; seepage andspraying of noncorrosive liquidsincluding oils and coolants.

UL 50/UL 508 Type 1IndoorIndoor enclosure providing adegree of protection from contactwith enclosed equipment and fromlimited amounts of falling dirt.

UL 50/UL 508 Type 2Water-resistant - IndoorEnclosure resistant to limitedamounts of falling water and dirt.

UL 50/UL 508 Type 3OutdoorOutdoor enclosure providing adegree of protection fromwindblown dust, rain, and sleet.Undamaged by external iceformation.

UL 50/UL 508 Type 3RRain-resistant - OutdoorSame as UL 50/UL 508 Type 3also providing a degree ofprotection from falling rain andsleet.

UL 50/UL 508 Type 4Indoor/OutdoorIndoor/Outdoor enclosureproviding protection fromsplashing or hose-directed water,rain and windblown dust.Undamaged by the formation ofice on the enclosure.

UL 50/UL 508 Type 4XIndoor/OutdoorIndoor/Outdoor enclosure sameas Type 4 with added resistanceto corrosion.

UL 50/UL 508 Type 12Indoor IndustrialIndoor enclosure providing adegree of protection from dust,falling dirt, and dripping non-corrosive liquids.

UL 50/UL 508 Type 13Indoor IndustrialIndoor enclosure providing adegree of protection form dust andspraying of water, oil and non-corrosive coolants.


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CHAPTER 8: Pressure Reducing Valves (PRV’s)

SECTION I: OVERVIEW

Maintaining a Constant System Pressure• The discharge pressure for a booster system is dependent largely on the suction pressure,

and to a lesser degree on the flow rate. These conditions can vary greatly during thenormal, day-to-day operation of a system.

• A booster system must be able to deliver a reliable, constant system pressure in order tosatisfy the requirements of a particular application. This is accomplished by regulating thedischarge pressure of each pump using a pressure reducing valve, or PRV.

• The PRV reduces the system pressure according to the conditions at discharge to maintaina constant system pressure.

• The system is designed so that the discharge pressure from the individual pumps alwaysexceeds the desired system pressure. This overage is then reduced to the desired systempressure by the PRV.

• The action of the PRV will account for variations in pump performance across the pumpcurve and for variations in the system supply (suction) pressure.

PRV ComponentsThe PRV can be broken down into two main assemblies:

a) The main body valve assemblyb) The pilot assembly

The dashed line seperates the internal main body valve and the external pilot assembly.


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• The main body valve assembly is the portion of the PRV through which the main flowtravels. The main body valve consists of the following parts and subassemblies:

a) The valve coverb) The cover springc) The main body diaphragmd) The valve steme) The seal and retainer assemblyf) The main body seatg) The strainer

(a)(b)(c)

(d)

(e)(f)

(g)

Main body valve components and subassemblies.

• The pilot assembly controls the opening and closing of the main body valve. The main bodyvalve is, in fact, slave to the pilot setting. Opening the pilot valve will open the main bodyvalve. Closing the pilot will close the main body valve.


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The components of the pilot assembly are as follows:

a) The pilot pressure reducing valve (with diaphragm)b) The in-line check valvesc) The piping assemblyd) The closing speed control

(a)(b)

(c)

(d)

(b)

Pilot assembly and components.

SECTION II: HOW the PRV WORKS

• To effectively regulate the system pressure, the PRV must change the amount of pressurereduction depending on the pressure of the incoming flow. This is accomplished by theopening and closing of the main body valve.

• As the pressure of the flow entering the PRV increases, the main body valve closescausing a greater reduction in the out-flow pressure. Conversely, as the in-flow pressuredecreases, the main body valve opens causing a lesser reduction in the out-flow pressure.


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FLOWOPENING

CLOSING

Flow through the main body valve is controlled by varying the pressure in the pilot assembly. This is doneby turning the set screw on the pilot pressure reducing valve. Closing the screw (as shown by the dark

arrows) prevents flow through the top piloting tube. This causes pressure to build up on top of thediaphragm, closing the main valve. Opening the screw (as shown by the light arrows) increases flow through

the top piloting tube. This reduces the pressure on top of the diaphragm causing the main valve to open.

• The action of the main body valve is regulated by the piloting system. As the incomingpressure increases, so does the pressure in the pilot circuit. This pressure is transmitted tothe top of the diaphragm forcing the valve closed. A reduction in pressure causes thereverse effect opening the valve.

• Why does the pilot “win out” over the main valve? The pressure above the diaphragm isexerted over an area 1.5 times greater than the seat area through which the main flow musttravel. This area differential gives the pilot an advantage (a type of hydraulic leverage),enabling it to control the action of the main valve.

Fig.# 5: The pilot pressure “wins out” over the flow pressure due to hydraulic leverage advantage.

PilotPressure

FlowPressureSeat Area

(Flow Area)

Diaphragm Area(Pilot Area)


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SECTION III: COMMON PRV ADJUSTMENTS

• The performance of the PRV’s in a booster are critical to the optimal performance of theentire system. Occasional adjustments and maintenance are required in order to keep thesystem running smoothly. Often, an improperly set or damaged PRV will show itself in thebooster system’s overall behavior.

• The symptoms of PRV problems are not difficult to recognize. PRV’s sometimes will notclose, will not open, or will not regulate the pressure at the set point. The causes of thesymptoms can be more difficult to diagnose. In general, before you begin to dissasemble aPRV, it is advisible to first check that the problem is with the PRV.

• This section discusses some of the most common problems encountered with PRV’s.• When encountering PRV reguating problems, first check that the system around the PRV is

running properly. During normal operation all isolation ball valves to and from the PRVshould be open. Check that the closing speed control and pilot valves are not closed. Youmay then want to inspect the PRV for leaks and visible damage.

• Before begining the following procedures, close the isolation ball valves to the PRV inquestion.

Stem Binding• This is an easy test to perform before you fully dissasemble the PRV.• Insert a 2 to 3” 10-32 screw into the tapped stem at the centre of the main body cover.

Using a set of pliers, pull the screw outwards. The stem should freely travel as you performthis action.

Air in Control Circuit or Pilot• Air in the PRV pilot assembly must be bled off at startup and can sometimes become a

problem if the system is shut down for an extended period of time.• To begin this procedure, open the isolation ball valves to the PRV. Carefully open the

check valve cocks allowing some water to bleed out. This will vent any trapped air in thepilot piping and under the main body valve cover.

Clogged Strainer• The strainer can be removed from the main body valve after closing the PRV isolation ball

valves.• The strainer is mounted on a brass fitting just below the seat assembly. Remove this fitting

and clean the strainer of any debris.

Diaphragm Failure• The two diaphragms of the PRV are subject to wear and occasionally require replacement.• Main body diaphragm failure is characterized by the inability of the PRV to close. A

ruptured main body diaphragm upsets the pressure balance inside the valve causing it tofly open.

• To replace a damaged diaphragm, remove the valve cover and the two nuts mounted onthe stem. Pull away the diaphragm washer plate, and remove and replace the diaphragm.

• Pilot diaphragm failure is easier to diagnose. The pilot valve will leak water if the diaphragmis damaged.

• To replace, simply remove the four screws on the pilot cover being careful not to lose thespring and retainer. Remove and replace the diaphragm.


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Seal Failure• Seal failure is characterized by failure of the PRV to close.• Replacing the seal on a PRV is probably the most involved maintenance procedure you will

be required to perform. The procedure is simple, but you must be careful to replace partscarefully on reassembly. Be especially careful not to damage the diaphragm and to replaceboth nuts on the stem.

• Remove the main body cover and diaphragm. Remove completely the stem and sealretainer assembly.

• The most common seal repair is replacement of the seat or the stem ‘O’-ring.• You will see that the seal retainer has a top plate, the retainer, and a bottom plate, the

“Quad-Seal” retainer plate. The “Quad-Seal” plate is fastened to the stem, but the retainerwill come free. With a mallet made of a soft material, gently tap the top of the stem whileholding the retainer. The plate will come free allowing you to remove and replace either ofthe ‘O’-rings.

Tip: The seat ‘O’-rings are reversible. Each has two seal surfaces and can be reversed to provide double the life of an ordinary ‘O’-ring.

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