Pumps Selection and Sizing and Troubleshooting

Department of Polymer and Process Engineering,

University of Engineering and Technology, Lahore

Fluid Flow (Lab)Subject Code: PolyE- 203

Topic:Selection of Pumps

and their Sizing,Their Materials of

Cinstruction and Troubleshooting

Group PresentationGroup#6

Grooup Leader:

Mujadid ul Hassan Khawaja

2010-PE-51 Department of

Polymer and Process Engineering, UET Lahore

Members

Syed Mohsin Ali Rizvi



Members

Hafiz Adnan Mehmood



Table of Contents:

1. Introduction to Pumps2. Major Classification of pumps and their

Working3. Materials of Construction of Pumps4. Some important terminologies related

to Pumps5. Selection of Pumps6. Sizing, Metering and proportionating

of pumps7. Troubleshooting of pumps

1.Introduction to Pumps And their Classification

Presenter:Mamoon Shahid

What are pumps

Pumps are device used to move fluids. They move fluids by using mechanical action.

Component of pumping system

The main components of a pumping system are:

Prime movers: electric motors , diesel engines or air system.

Piping, used to carry the fluid.

Valves, used to control the flow in the system.

Classification of pumps

Pumps

Dynamic Positive

displacement pump

Axial Flow Pumps

1. Single Stage Pump

Axial Flow Pumps

Opened, Closed and Semi Closed Impellers

Centrifugal Pumps on the Basis of Suction Postition

Dynamic pumps

Energy is added to fluid velocity

At discharge end velocity is reduced and pressure is increased

There are two types of dynamic pump1.Centrifugal pump2.Special effect pumps

Centrifugal pump

Its purpose is to convert energy of a prime mover first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped.

A centrifugal pump can be single stage or multi stage.

Working mechanism

Working mechanism can be expressed in two steps

1) Generation of centrifugal forces

2) Conversion of kinetic energy to pressure energy

Generation of centrifugal forces

The process liquid enters the suction nozzle and then into eye (center) of a revolving device known as an impeller.

When the impeller rotates, it spins the liquid.

Because the impeller blades are curved, the fluid is pushed in a tangential and radial direction by the centrifugal force.

Conversion of kinetic energy to pressure energy

The key idea is that the energy created by the centrifugal force is kinetic energy.

The faster the impeller revolves or the bigger the impeller is, then the higher will be the velocity of the liquid at the vane tip and the greater the energy imparted to the liquid.

Conversion of kinetic energy to pressure energy

This kinetic energy of a liquid coming out of an impeller is harnessed by creating a resistance to the flow. The first resistance is created by the pump volute (casing) that catches the liquid and slows it down.

In the discharge nozzle, the liquid further decelerates and its velocity is converted to pressure according to Bernoulli’s principle.

Working mechanism

Energy changes

Impeller Diffuser

Components of a centrifugal pump

The main components of a centrifugal pump are

1. Rotating components: an impeller coupled to a shaft.

2. Stationary components: casing, casing cover, and bearings.

Impeller

An impeller is a circular metallic disc with a built-in passage for the flow of fluid.

Impellers are generally made of bronze, polycarbonate, cast iron or stainless steel, but other materials are also used.

Shaft

• The shaft transfers the torque from the motor to the Impeller during the startup and operation of the pump.

Shaft

Casing

The main function of casing is to enclose the impeller at suction and delivery ends.

A second function of casing is to provide a supporting and bearing medium for the shaft and impeller.

Volute casing

A volute is a curved funnel increasing in area to the discharge port .

Circular casing

Circular casing has stationary diffusion vanes surrounding the impeller periphery that convert speed into pressure energy.

2.Postive Displacement

Pumps,Their Major Types and

working

Presenter:Hafiz Adnan Mehmood

Positive Displacement Pumps

Contents Introduction

Construction & working

Types

Introduction

A positive displacement pump is one in which a definite volume of liquid is delivered for each cycle of pump operation. This principle applies to all types of positive displacement pumps

Construction & working

Positive Displacement Pumps has an expanding cavity on the suction side and a decreasing cavity on the discharge side.

Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses.

Working and Construction

A Positive Displacement Pump must not be operated against a closed valve on the discharge side of the pump because it has no shut-off head like Centrifugal Pumps.

A Positive Displacement Pump operating against a closed discharge valve, will continue to produce flow until the pressure in the discharge line are increased until the line bursts or the pump is severely damaged - or both.

http://www.engineeringtoolbox.com/centrifugal-pumps-d_54.html

http://www.engineeringtoolbox.com/centrifugal-pumps-d_54.html

Working and Construction Positive Displacement Pumps are "constant

flow machines“.

A relief or safety valve on the discharge side of the Positive Displacement Pump is therefore absolute necessary.

The relief valve can be internal or external.

Types

There are two main types of PD pumps

Reciprocating pumps

Rotary pumps

Reciprocating pumps

Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms).

Plunger pumps

Diaphragm pumps

Diaphragm pump

Plunger pump

Working of Plunger pump Plunger pumps comprise of a cylinder

with a reciprocating plunger in it.

In the head of the cylinder the suction and discharge valves are mounted. In the suction stroke the plunger retracts and the suction valves opens causing suction of fluid into the cylinder.

In the forward stroke the plunger push the liquid out the discharge valve.

Rotary Pumps

Displacement by rotary action of gear, cam or vanes

Typical rotary pumps are

Gear pumpsLobe pumpsVane pumpsCam pumpsScrew pumps

Gear pumps

Cont. . .

In gear pumps the liquid is trapped by the opening between the gear teeth of two identical gears and the chasing of the pump on the suction side.

On the pressure side the fluid is squeezed out when the teeth of the two gears are rotated against each other.

the gear pump is well suited for handling viscous fluids such as fuel and lubricating oils.

Rotary pumps are further classified such as internal gear, external gear, lobe and slide vane etc

Lobe pumps

Effects of Pressure & Viscosities on PD Pumps

PressureChange in Pressure have little effect on the

PD pump efficiency.

ViscosityWhen the viscosity of fluid increases the

flow also increase in PD pumps. The reason is the liquid fill in the clearances of the pump causing a higher volumetric efficiency .

•if there is changing viscosity in the application the PD pumpis the best choice.

Presenter:Mohsin Ali Rizvi

4. Materials of

Constructions of Pumps

Material of construction

The pumps have different parts ; Impeller , casing , shaft and wear rings etc When selecting the material for the impeller, the following several criteria

should be considered

Corrosion resistance

Abrasive wear

resistance

Cavitations resistance

Casting & machining properties


Bronze Impellers used for many water and noncorrosive services but these impellers should

not be used for pumping temperature in excess of 120°C Types:

1. Leaded bronze2. Non leaded bronze3. Nickel aluminum bronze

Leaded bronze Impellers Used extensively in past because the lead addition to bronze enhances its

cast ability and machine ability but due to environmental problems they have been replaced by Non-leaded bronze impellers.

Bronze Impellers

Material Of Construction

Non-Leaded Bronze Impellers Although they are efficient than leaded bronze impellers but they have velocity

limitations above which they cannot be used because they will suffer accelerated erosion corrosion. So they are used where not so high speed is required.

Nickel Aluminum Bronze Impellers These impellers are used specially in salt water applications because of their high

mechanical properties, good corrosion resistance and the capability to be weld repaired. They are also designed for higher speed than any other bronze alloy impellers.

Cast iron Impellers They are used to a limited extent in small ,low cost pumps. This material is inferior

than bronze in corrosion and cavitation resistance also it can not be welded to repair damage. So only the low cost is the mere justification for the cast iron impeller usage.


Martensitic Stainless Steel Impellers They are used in the place of bronze impellers where bronze does not satisfy the

requirements for cavitation resistance, corrosion and erosion. These impellers are used in boiler feed water, many cooling waters and a variety of cooling applications They do not have pitting corrosion for use in sea water.

Martensitic Stainless Steel Impellers These impellers are used where higher level of corrosion resistance is required.

1. Austenitic grades having 6% molybdenum for use in salt water2. Austenitic grades having 20% nickel for the sulphuric acid applications3. Chrome manganese alloy to eliminate cavitation resistance


Duplex Stainless Steel These impellers are used because of their higher mechanical properties, better corrosion

resistance and weld ability. Nitrogen addition in it improves its cast ability and weld ability. These impellers are widely used in mining ,flue gas desulfurization, paper and pulp industry and for the marine applications. Specially they are used in high pressure water injection in the oil industry.

It should contain 25% chromium, 3%molybdenum and 0.15% nitrogen.


When selecting the material for the Casing of pump, the following several criteria should be considered


Abrasive wear

resistance

Cost and strength

Casting & machining properties

Weld ability (for repair)&

cost


Cast iron Casing

For single stage pumps , cast iron casing is used because it has sufficient for pressure developed. (discharge pressure up to 1000lb/sq.inch and temperature up to 177 C).

For multi-stage pumps and pressure up to 2000lb/sq.inch a cast steel is used and for the pressure above this forged steel barrel type casing is used.

Ductile iron casing can be used instead of cast iron as its tensile strength is double as compared to cast iron. They can used as a substitute for steels in the intermediate temperature range. But they can not be effectively repaired or welded


Austenitic Irons Casing They are commonly known by their trade name Ni-resist, are used where ductile irons have

insufficient corrosion resistance. They typically contain 15-20% Ni and are used in brackish and salt water applications. But they poor towards welding that’s why its new modified grade D2W is used which

contains columbium that enhances its weld ability.

Bronze Casing Leaded bronze, Non-leaded bronze, Tin bronze, Ni-Al bronze are alloys used for the casing

depending upon the application. Among them Ni-Al type is expensive and are usually not competitive on cost basis with Ni-resist or other alternatives


Steel Casings

1. Stainless Steel2. Martensitic stainless Steel3. Austenitic Stainless Steel4. Duplex Stainless Steel All these materials have their own usage according to applications. The first one is used

for better corrosion resistance, second one is used for high pressure applications and in many hydrocarbons applications, the third one in chemical applications and corrosive services and Duplex is used where corrosion resistance and mechanical properties higher than other austenitic grades are required


When selecting the material for the shaft, the following several criteria should be considered


wear resistance

Cost and strength

Endurance limit

Notch sensitivity


The several materials for shaft are available according to the specifications.

1. Carbon steel 2. Stainless steel 3. Martensitic stainless steel etc These materials should have low cost and high wear resistance and good endurance limit that’s

why a shaft can be plated or coated for an improved corrosion resistance and wear. Chrome plating is one of the example.


When selecting the material for the Wear rings, the following several criteria should be considered


Abrasive wear

resistance

Casting and machining properties

Galling characteristi

cs

suitability for coating


The several materials are available for wear rings according to the Applications.

1. Bronze2. Stainless Steel3. Martensitic stainless steel Bronze is used for wear rings because it exhibits good

corrosion resistance for wide range of water services and tends to wear rapidly when abrasive particles are used. Due to this limitation Stainless steel is used. Martensitic stainless steel wear rings are usually hard and they are more resistant towards wear because of increased surface hardness. Tungsten carbide is used for high hardness and resistant to abrasion

Presenter:Mujadid ul Hassan Khawaja

5.Selection of Pumps

Selection of Pumps

The selection of a pump type for a particular application is influenced by a variety of factors. Such as:

Fluid Characteristics Required material of construction System Flow and Head Requirements Intended Equipment life Energy Cost Availabilty of certain uitlities

1. Pump Types

There are several different types of basic pump designs

Every pump design can be used for a range of flow and head combination

Flow and head range charts for pumps can help in this respect

There are other factors upon which can help us in selecting a suitable pump for a given application

2. Self Priming Requirements

When does the self priming factor becomes important and necessary in pumping????

“If a pump is taking suction from a source below the pump suction nozzle”

Positive displacement pumps are able to self prime within limits in the smaller capacity range

Some special types of centrifugal pumps can also do self priming

3.Variable Head/Flow Requirements

Centrifugal and Axial flow pumps are available to operate in variable head/flow conditions

The head flow range of the pumps can be determined by the their respective pump characteristic curve

This curve gives us information about different characteristics (eg power, NPSH, efficiency)of a pump at different capacity and head requirements..

For a given impeller size, a pump can produce any flow rate within its characteristic curve, if sufficient NPSH is available


The system head characteristics can be changed to vary flow rate by

Discharge ThrottlingVarying Pump speed

Some pump Characteristic curves are as follows:

http://www.veoliawaterst.com/processes/link/download?site=doc&objectId=1930

4. High Head Requirement

After selecting the required flow rate, either a centrifugal or a piston pump may fulfill the need for high differential head required.

If a small flow rate is required, either an integrally geared centrifugal pump or a piston pump may be applied

For High flow and high head combinations, a multi stage centrifugal pump can be used.

5. Low Flow with Precise Adjustment Ability

A proportioning pump is appropriate for such application

This type of pump can also be provided with variable flow capacity

Certain types of gears, plungers, diaphragm pumps can also be used in combination with a variable speed drive for flow rate regulation.

NPSHR and NPSHA NPSHR is the amount of liquid pressure required at

the intake port of a pre-designed and manufactured pump.

NPSHA is the amount (A = available) to the pump intake after pipe friction losses and head pressures have been taken into account.

The NPSHA must equal or exceed the NPSHR. The available NPSH is a characteristic of the piping system.

If the NPSHA is lower than the NPSHR then gas bubbles will form in the fluid and caviation will occur.

The NPSHA is calculated from:

6. Low available Net Positive Suction Head (NPSHA)

If the available NPSH is low, specially designed Centrifugal pumps may be used

Depending on how low the NPSH is, either : Horizontal end suction pump with a suction inducer OR A double Suction arrangement may be

applied A vertical Turbine pump may also be used for

this purpose

7. Fluid Characteristics

Is the liquid? Fresh or salt water, acid or alkali, oil,

gasoline, slurry, or paper stock? Cold or hot and if hot, at what

temperature? What is the vapor pressure ofthe liquid at the pumping temperature?

What is its specific gravity? Is it viscous or non-viscous? e. Clear and free from suspended foreign

matter or dirty and gritty?


If the latter, what is the size and nature of the solids, and are they abrasive?

Ifthe liquid is of a pulpy nature, what is the consistency expressed either in percentage or in 1b per cubic ft of liquid? What is the suspended material?

f. What is the chemical analysis, pH value, etc.? What are the expected variations of this analysis?

If corrosive, what has been the past experience, both with successful materials and with unsatisfactory materials


For a highly viscous fluids such as Toothpaste, peanut butter, and shampoos, a positive displacement progressing cavity pump can be used

A rotary variable displacement piston pump might be used for hydraulic control system, but it is not a good choice for potable water application.

For pumping hot asphalt and some other limited applications in lube oil systems, a rotary sliding vane pump can be used.

8. Pump Materials

Material selectin is affected both by 1. The fluid being pumped 2. The environment. Resistance to corrosion and erosion are of

prime importance . The engineer must determine which material

is most suitable for a particular service. Pumps are commonly available in cast iron,

ductile iron, carbon steel, alloy steel, and in some composite materials or special alloys such as Monel, Hastelloy or Titanium.

9. Driver Selection

The choice of driver is as important as the pump selection

Factors affecting the driver choice are:

1. Capital Cost 2. Driver type availability 3. operation reliability 4. Availability and cost of utilities 5. RPM required for the process

6.Metring or Proportioning

And Sizing of Pumps

.

Presenter:Muhammad Belal Malick

Delivery of fluids in precise adjustable flow rates is called metering.

A metering pump is a pump used to pump liquids at adjustable flow rates which are precise when averaged over time.

The term "metering pump" is based on the application or use rather than the exact kind of pump used, although a couple types of pumps are far more suitable than most other types of pumps.

Principle

This class of pumps moves liquids in two stages: the suction stroke and the discharge stroke.(Reciprocating)

The basic principle of metring is to change the displacement per stroke or the stroking speed.

What type of pumps can be metered?

Positive displacement reciprocating pumps can be adapted to function as metring or proportioning devices.

Three basic types of pumps with several variations can be used for this service:

Packed Plunger pump(piston pump) Mechanically actuated diaphragm pump Hydraulically actuated diaphragm pump

Packed Plunger Pump

Mechanically Actuated Diaphragm Pump

Hydraulically Actuated Diaphragm Pump

Capacity Cotrol

Manually adjusted while stopped Manually adjusted while running Pneumatic Electric Variable Speed

Manually adjusted while stopped

Manually adjusted while running

Pump Sizing

Sizing a pump is to figure out the presure required to pump the gallons per minute of fluid.

There are two items required to size a pump:

Fluid flow rate Pressure to be developed

Pump performance curve A Pump Performance Curve is produced by a pump manufacturer from actual tests performed and shows the relationship between Flow and Total Dynamic Head(TDH) or presure.

System Curve

The system curve is a plot of the Total Head vs. the flow for a given systems.

Operating Point

The rate of flow at a certain head is called the duty point. The pump performance curve is made up of many duty points. The pump operating point is determined by the intersection of the system curve and the pump curve as shown in Figure.

Not all system operating points are directly on top of a pump graph or curve as shown below:

It would be best to choose a pump on the curve above the operating point.

If a pump has three speeds then three curves will be shown:

It would be best to operate a pump at a lower speed if possible to prolong the life of the pump and bearings.

PUMPS IN PARALLEL TO MEET VARYING DEMAND

Operating two pumps in parallel and turning one of

when the demand is lower, can result in significant

energy savings. Pumps providing different flow rates

can be used. Parallel pumps are an option when the

static head is more than fifty percent of the total

head.

If W is negative a pump is required; if it is positive a turbine could be installed to extract energy from the system.

The power is given by:

where m = mass flow-rate, kg/s,

η — efficiency = power out/power in.

Power requirements for pumping liquidsThe total energy required can be calculated from the equation:

where W = work done, J/kg,

Δz = difference in elevations , m,

ΔP = difference in system pressures , N/m2,

ΔP= pressure drop due to friction, including miscellaneous losses,

and equipment losses, N/m2,

p = liquid density, kg/m3,

g = acceleration due to gravity, m/s2.

Pump Efficiency

The efficiency of a pump is a measure of the degree of its hydraulic and mechanical perfection.Pump efficiency is expressed in percentage as:

Pump Efficiency =GPM X Total Head X 100/(input HP X 3,960)

HorsePower=HP= A unit of power equal to 745.7 watts.

B.E.P. (best efficiency point)

The pump's efficiency varies throughout its operating range.

The efficiency will depend on the type of pump used and the operating conditions.

The B.E.P. (best efficiency point) is the point of highest efficiency of the pump.

All points to the right or left of the B.E.P have a lower efficiency.

Under sizing of pumps

Undersizing the zones will cause the pump to cycle often.

wears out the motor

excessive overload tripping

Over sizing of Pumps

Operation requires greater NPSH

High pressure drop

Cavitation

Greater power consumption

High purchase cost

Vibration

Keeping in Mind!

Higher Head = Lower FlowLower Head = Higher FlowLower Flow = Lower power

Higher Flow = Higher power

7. Troubleshooting

of Pumps

Presented by:Shahzab Idrees

Suction Problems

Mechanical Problems

System Problems

Hydraulic Problems

Troubleshoots

Troubleshoots in Centrifugal Pumps:

Suction Problems:

Pump not primed Insufficient available NPSH Air leaks into suction line Vortex formation at suction Excessive friction losses in suction line Clogged impeller Selection of pump with too high suction

speed

Troubleshoots in Centrifugal Pumps: Symptoms:

Pump does not deliver liquid Insufficient capacity Requires excess power Vibration Overheating and Seizing Impeller vanes are eroded Corrosion Mechanical seal leaks Coupling fails


Hydraulic Problems:

Speed of pump too high/low Wrong direction of rotation Static head higher than shut-off head Total head of system higher/lower than

design of pump Excessive wear


Mechanical Problems:

Foreign matter in impeller Misalignment Bent shaft Rotor out of balance Parts loose on shaft Shaft running off-center because of wrong bearings Incursion of hard particles into running clearance Inadequate tightening of casing bolts Pump material not suitable for liquid handled

Troubleshoots in rotary pumps:

Symptoms:

Pump fails to discharge Noisy Wear rapidly Pump starts, then loses suction Takes excessive power

Troubleshoots in rotary pumps: Suction Problems:

Pump not properly primed Suction pipe not submerged Foot valve leaking Suction pipe too small

Mechanical Problems: Pump worn Air leak Pipe strain Corrosion

Troubleshoots in rotary pumps:

System Problems:

Wrong direction of rotation Low speed Insufficient liquid supply Pump runs dry

Troubleshoots in reciprocating pump:

Symptoms

Noise Oil leak Overheated Water in crankshaft Loss of prime Pitted valves

Troubleshoots in reciprocating pump:

Suction problems: Insufficient suction pressure Cavitation Lift too high

System problems: System shooks Overpressure/ overspeed Dirty environment Air in liquid

Troubleshoots in Steam pumps:

Symptoms:

Does not develop rated pressure Lose capacity Vibrates Operation is erratic

Troubleshoots in Steam pumps: Suction Problems:

Suction line leaks Suction lift too high Cavitation

System Problems: Low steam pressure High exhaust pressure Entertained air or vapors

Mechanical Problems: Worn piston rings Misalignment Piping not supported

Pumps Selection and Sizing and Troubleshooting

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