group maintenance - pump

8/8/2019 Group Maintenance - Pump

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Table of Contents

1.0 Introduction

2.0 Types of Pump

2.1. Positive-Displacement Pump

2.2. Dynamic Pump

2.3. Comparison between Centrifugal Pumps and Positive-Displacement

3.0 Basic Pump Component

3.1. Types of Impeller

3.1.1. Open Impelled

3.1.2. Closed Impelled

3.1.3. Comparison between Open and Closed Impeller

3.2. Mechanical Seal

4.0 Pump Terms

5.0 Standard of Design

6.0 Analysis

6.1. Hydraulic power 6.2. Specific Speed

6.3. Net Positive Suction Head

6.4. Reading a Pump Performance Curves

6.5. Pump Operating Range

7.0 General Installing Method

7.1. Installation of Pump, Motor and Base

7.2. General Piping Requirement

7.3. Suction Piping

7.4. Discharge Piping

7.5. Suction Head (Flooded Suction) Conditions

7.6. Suction Lift Conditions

8.0 General Precautions

9.0 Inspection of System

10.0 Troubleshooting

11.0 Pump Enquiry Information

Appendixes

Appendix A Types of Pump and Basic Components

Appendix B Service Liquid

Appendix C Pump Performance Curves



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1.0 Introduction

Pump is the oldest f luid-energy-transf er device knows. For examples, the under-shot-bucket

waterwheels and Archimedes screw pump, still being manuf actured today to handle solid-liquid

mixtures. A pump displaces a volume by physical or mechanical action.

2.0 Types of Pump

There are two types of pump: positive-displacement and dynamic pumps

2.1. Positive-Displacement Pump

Positive-displacement pumps (PDPs) force the f luid along by volume changes. A cavity opens, and

the f luid is admitted through an inlet. The cavity then closes, and the f luid is squeezed through an

outlet. A brief classification of PDP designs is as follows:

y Reciprocating

o Piston pump

o Diaphragm pumpy Rotary motion

o Lobe pump

o Screw pump

o Helical screw pump

o Gear pump

y Big positive-displacement pump

All PDPs deliver a pulsating or periodic f low as the cavity volume opens, traps, and squeezes the

f luid. Their great advantage is the delivery of any f luid regardless of its viscosity. PDP can operate up

to very high pressures (300 atm) but typically produces low f low rates (100 gal/min).

PDPs are found in a wide range of applications of chemical-processing, liquid delivery, marine

biotechnology, and pharmaceutical as well as food, dairy and beverage processing.

2.2. Dynamic Pump

Dynamic pumps simply add momentum to the f luid by means of f ast-moving blades or vanes or

certain special designs. There is no closed volume. The f luid increase momentum while moving

through open passages and then converts its high velocity to a pressure increase by exiting into a

diffuser section. Dynamic pumps can be classified as follows:

y Rotary

o Centrifugal pump

o Axial f low pump

o Mixed f low pump

y Special designs

o Jet pump or ejector

o Electromagnetic pump for liquid metals

o Fluid-actuated for gas-lift or hydraulic-ram



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Dynamic pumps generally provided a higher f low rate than PDPs and a much steadier discharge but

are ineff ective in handling high-viscosity liquids. Adynamic pump can provide very high f low rate (up

to 300.000 gal/min) but usually with moderate pressure rises (a f ew atmospheres).

Dynamic pumps are found is wide range of applications of irrigation, water supply, gasoline supply,

air conditioning system, refrigeration, chemical movement, sewage movement, f lood control and

marine services. Due to the wide variety, pumps have a diff erent shapes and sizes. This is based on

the usage industrial requirements.

*All the diff erent types of pump are shown in Appendix A.

2.3. C omparison betweenC entrifugal Pumps and Positive-Displacement Pumps

Parameter Centrifugal pumps PDPs

Optimum f low and pressure

application

y Medium/high capacity

y Low/medium pressure

y Low capacity

y High pressure

Maximum f low rate y 100,000+GPM y 100,000+GPM

Low f low rate capability y No y Yes

Maximum pressure y 6,000+PSI y 100,000+PSI

Requires relief valve y No y Yes

Smooth or pulsating f low y Smooth y Pulsating

Variable or constant f low y Variable y Constant

Self -priming y No y Yes

Space consideration y Requires less space y Requires more space

Costs

y Lower initial

y Lower maintenance

y Higher power

y Higher initial

y Higher maintenance

y Lower power

Fluid handling

y Suitable for a wide

range including clean,

clear, non-abrasivef luids to f luids with

abrasive, high-solid

content

y Not suitable for high

viscosity f luids

y Lower tolerance for

entrained gases

y Suitable for clean,

clear, non-abrasive

f luids.y Specially-fitted pumps

suitable for abrasive-

slurry service

y Suitable for high

viscosity f luids

y Higher tolerance for

entrained gases

3.0 Basic Pump Component

There are two main components of a centrifugal pump which are the impeller and the volute/casing.

The impeller produces liquid velocity and the volute forces the liquid to discharge from the pump

converting velocity to pressure. This is accomplished by off setting the impeller in the volute and by

maintaining a close clearance between the impeller and the volute at the cut-water.

*The sectional drawing of a centrifugal pump and typical pump assembly are shown in Fig 3&4,

Appendix A.



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3.1. T ypes of Impeller

Impeller is a rotating component. It is usually made of iron, steel, bronze, brass, aluminium or plastic

which transf er energy from the motor that drives the pump to the f luid being pumped by

accelerating the f luid outward from the center of rotation. Impeller usually is a short cylinder with an

open inlet (called eye) to accept incoming f luid. Then the f luid will be push by the vanes to drive-

shaft.

Impeller can be classified into open impeller and closed impeller. Both impellers are shown at Fig

5&6 from Appendix A.

3.1.1. O pen Impeller

y Fluid enters the eye of the impeller where the turning vanes add energy to the f luid

and direct it to the discharge nozzle. A close clearance between the vanes and the

pump volute, or the back plate in a f ew designs. This is to prevent most of the f luid

from recirculating back to the eye of the impeller.

3.1.2. C losed Impeller

y Fluid enters the eye of the impeller where the vanes add energy to the f luid and

direct it to the discharge nozzle. There is no impeller to volute or back plate

clearance to set

y Wear rings restrict the amount of discharge f luid that recirculates back to the

suction side of the impeller. When this wear ring clearance becomes excessive, the

wear ring must be replaced.

3.1.3. C

omparison betweenO pen and C

losed Impeller

Closed impeller Open impeller

Can compensate for shaft thermal growth, but if

there is too much axial growth the vanes may

not line up exactly with the discharge nozzle

The impeller to volute or back plate clearance

must be ad justed when the pump is at operating

temperature and all axial thermal growth has

occurred.

Good for volatile and explosive f luids because

the close clearance wear rinds are the parts that

will contact if the shaft displaces from its

centreline.

Soft and non-sparking materials for impeller are

not very practical.

The impeller is initially very efficient, but loosesits efficiency as the wear ring clearance increases Efficiency can be maintained through impeller clearance ad justment.

No impeller ad justment is possible. Once the

wear rings clearances doubles they have to be

replaced. This means the pump had to be

disassembled just to check the status of the wear

rings

The impeller can be ad justed to compensate for

wear and stay close to its best efficiency. No

pump disassembly is necessary

The impeller can clog if the pump solids or

stringy material. It is difficult to clean out these

The open impeller is less likely to clog with

solids, but if it does, it is easy to clean



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solids from the shrouds and vanes

The impeller is difficult to cast because the

internal parts are hidden and hard to inspect for

f laws

The open impeller has all the parts visible.

The closed impeller is more complicated and

expensive design not only because of the

impeller, but the additional wear rings areneeded.

The pump is less costly to build with a simple

open impeller design.

The impeller is difficult to modif y to improve its

performance

The vanes can easily be cut or filled to increase

capacity.

The specific speed choices and the shape of the

impeller are limited

Greater range of specific speed choices

3.2. Mechanical Seal

Mechanical seal is a device which helps join systems or mechanisms together by preventing leakage,

containing pressure, or excluding contamination. A seal may also be ref erred to as packing. There

are a f ew mechanical seal which are:

y Single mechanical seal

y Double mechanical seal

y Tandem seal

y Mechanical seal coding

y Conventional packing

4.0 Pump Terms

y Head

o Centrifugal pump curves show pressure as head, which is the equivalent height of

water with S.G. = 1. This makes allowance for specific gravity variations in the

pressure head conversion to cater for higher power requirements.

y Static Head

o The vertical height diff erence from surf ace of water source to centreline of impeller

is termed as static suction head or suction lift (total suction head).

o The vertical height diff erence from centreline of impeller to discharge point is

termed as discharge static head.

o The vertical height diff erence from surf ace of water source to discharge point is

termed as total static head.

y Total Head / Total Dynamic Head

o Total height diff erence (total static head) plus friction losses and demand pressure

from nozzles

y Net Positive Suction Head (NPSH)

o Related to how much suction lift a pump can achieve by creating a partial vacuum.



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o Atmospheric pressure then pushes liquid into pump

o To prevent cavitations

y Specific Speed

o A number which is the function of pump f low, head and efficiency.

o Not used in day to day pump selection, but very useful as pumps with similar specific speed will have similar shaped curves, similar specific speed will have similar shaped

curves, similar efficiency / NPSH / solid handling characteristics.

y Vapour pressure

o If the vapour pressure a liquid is greater than the surrounding air pressure,the liquid

will boil.

y Viscosity

o A measure of a liquids resistance to f low.

o Determines the type of pump used, the speed it can run at and with gear pumps, the

internal clearance required.

y Friction Loss

o The amount of pressure / head required to force liquid through pipe and fittings

5.0 Standards of Design

Standards of design and dimensional specifications are necessary to bring unity to pumps. Standards

are provided by organizations like:

y ISO International Standards Organizations

y API American Petroleum Institute

y ANSI American National Standards Institutey DIN Deutsches Institut fur Normung

y NPFA National Fire Protection Agency

y BSi British Standards Institute

6.0 Analysis

6.1. H ydraulic Power

The work performance by a pump is a function of the total head and the weight of the liquid

pumped in a given time period. The term is:

Where,



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6.2 Specific Speed

Specific speed is a non-dimensional design index that identifies the geometric similarity of pumps. It

is used to classif y pump impellers as to their type and proportions. The following formula is used to

determine specific speed:

Where,

Specific speed identifies the approximate acceptable ratio of the impeller eye diameter, D1 to the

impeller maximum diameter, D2 in designing a good impeller.

y Ns: 500 to 5000; D1/D2 > 1.5 radial f low pump

y Ns: 5000 to 10000; D1/D2 > 1.5 mixed f low pump

y Ns: 10000 to 15000; D1/D2 > 1.5 axial f low pump

Specific speed is also used in designing a new pump size-f actoring a smaller pump of the same

specific speed. The performance and construction of the smaller pump are used to predict the

performance and model the construction of a new pump.

6.3 N et Positive Suction H ead ( N PSH)

NPSH shows the diff erence between the actual pressures of a liquid in a pump at a given temperature. Whenever the liquid pressure drops below the vapour pressure, liquid boiling occurs,

and the final eff ect will be cavitations. To overcome the problem, NPSH available must be greater

than NPSH required. Normally, it is advisable to allow approximately 1 metre diff erence for most

applications.

NPSH available can be calculated by:

NPSH = p + s v f

Where,

p = atmospheric pressure

s = static suction

v = liquid vapour pressuref = friction loss

6.4 Reading a Pump Performance C urves

y Pump performance is represented by multiple curves indicated either:

o Various impeller diameter at a constant speed

o Various speeds with a constant impeller diameter



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y The curve consists of a line starting at shut-off . The line continues to the right, with head

reducing and f low increasing until the end of curve is reached

y Flow and head are linked, the relationship between them is locked until wear or blockage

changes the pump characteristics.

y Ref er to Appendix C for sample curve showing.

o Three performance curves ( various impellers or speed)

o Curves showing power absorbed by pump (read power at operating point, at point 1)

o Best efficiency point (BEP)

o Recommended operating range

o NPSH required

y Power absorbed by the pump is at point where power curve intersects pump curve at

operating point.

o Select motor or engine to suit specific engine speed or operating range cost eff ective

method where operating condition will not vary greatly

o Read power at end of curve most common way that ensures adequate power at

most operating conditions

o Read power at operating point plus 10%

o By using system curves all operating conditions can be considered best method where filling a long pipelines, large variations in static head

6.5 Pump O perating Range

y BEP is not only the operating point of highest efficiency but also the point where velocity

and therefore pressure is equal around the impeller and volute. As operating point moves

away from the BEP, the velocity change, which changes the pressure acting on one side of

the impeller.

y Outside the recommended operating range will damage the pump due to excess velocity

and turbulence. The resulting vortexes can create cavitations damage capable of destroying

the pump casing, back plate, and impeller in a shortperiod.

y When selecting or specif ying a pump, it is important not to add saf ety margins or baseselection on inaccurate information. The actual system cure may cross the pump curve

outside the recommended operating range.

y The best practice is to confirm the actual operating of the pump during operation to allow

ad justment to ensure correct operation and long service lif e.

7.0 General Installing Method

7 .1. Installation of Pump, Motor and Base

o The foundation area must be firm and level for maintaining pump alignment.

o The pump and motor assembly must be securely f astened to the base, and the basemust be securely attached to the foundation.

o The pump inlet should be as close to the liquid source as practical and pref erably

below it.

o The pump and motor shouldbe accessible for servicing and inspection.

o The pump and motor should be cleaned periodically to prevent the build-up of dust.

o If the pump was delivered as a complete long-coupled assembly, it was properly

aligned at the f actory. However, alignment should be checked after installation to

ensure that the pump and motor are still aligned. Alignment can be checked by



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measurements at the coupling. Flexible couplings are not intended to compensate

for misalignment. Therefore, both angularity and parallelism should be checked and

corrected. If these are off by more than 0.015, the assembly should be realigned.

7 .2 General Piping Requirements

o All piping must be supported independently and must line up naturally with pumpports.

o DO NOT make final connection of piping to pump until the grout has hardened and

the pump and motor hold-down bolts have been tightened.

o Piping runs should be designed to minimize friction losses.

o Suction and discharge piping should be the same size or larger than the inlet and

outlet ports.

o Piping that handles both hot and cold liquids require proper installation of expansion

loops and joints so that thermal expansion of the piping will not cause misalignment.

o The piping should be arranged to allow the pump to be f lushed and drained prior to

the removal of the pump for servicing. Valves and unions should be installed to

allow the pump to be isolated during maintenance.

o

The piping system should be thoroughly cleaned prior to installation of the pump.o Gasket installation and materials must be suitable for the service.

7 .3 Suction Piping

o Properly installed suction piping is a necessity for trouble free pump operation. The

suction piping should be f lushed BEFORE connecting it to the pump.

o Use of elbows close to the pump suction port should be avoided. There should be a

minimum of five pipe diameters of straight pipe between the elbow and the suction

inlet. Any elbows used should be long radius.

o The suction pipe should be one or two sizes larger than the pump suction size, with

a reducer at the suction port. The diameter of the suction piping must never be

smaller than the pump suction port diameter.o Reducers, if used, should be eccentric at the pump suction port.

o Suction strainers, when used, must have a net free area of at least three times the

suction pipe area.

o Separate suction lines are recommended when more than one pump is operated

from the same supply.

7 .4 Discharge Piping

o Isolation valves should be installed in the discharge line. An isolation valve is

required for priming and regulating f low, and for isolating the pump for inspection

and maintenance.

o If quick closing valves are installed in the system, cushioning devices should be used

to protect the pump from surges and water hammer.

7 .5 Suction H ead (Flooded Suction ) C onditions o An isolation valve should be installed in the suction line to permit closing of the line

for pump inspection and maintenance.

o Piping should be level or slope gradually downward from the source of the supply.



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o The suction pipe must be submerged sufficiently below the liquid surf ace to prevent

vortices and air entrapment at the supply.

7 .0 Suction Lift C onditions

o The suction pipe must slope continuously upward towards pump suction to

eliminate air pockets.o All joints must be air tight.

o A means of priming the pump must be provided.

8.0 General Precautions

o Always lock out the power to the pump driver when performing maintenance on the

pump

o Always lock out the suction and discharge valves when performing maintenance on

the pump

o Never operate the pump without saf ety devices installed

o Never operate the pump with suction and/or discharge valves closed

o Never operate the pump out of its design specifications

o Never start the pump without making sure that the pump is primed o Never use heat to disassemble pump

o Inspect the entire system before start-up

o Monitor the system during operation and perform maintenance periodically or as

required by the application

o Decontaminate pump using procedures in accordance with f ederal, state, local and

company environmental regulations

o Before performing maintenance on the pump, check with appropriate personnel to

determine if skin, eye or lung protection is required and how best to f lush the pump

o When performing maintenance, pay special attention to all cautionary statements

given.

9.0 Inspection of System

o Pump Construction: The materials of construction of the pump must be compatible

with the f luid to be pumped.

o Pump Mounting: The pump must be securely f astened to the base and ground using

the basic installation procedures as outlined by the Hydraulic Institute.

o Alignment: Long-coupled pumps should be checked for proper alignment

o Piping Layout: Process piping procedures are extremely important and must be

performed in accordance with the Hydraulic Institute. As a minimum, inlet piping

must be equal to or larger in diameter than the pump inlet size. Twists and bends of

pump inlet piping should be kept to an absolute minimum. Ensure that adequate

NPSH is available for the pump to operate properly.o Valves: All suction and discharge valves must be open during start-up and operation

or damage or malfunction may result.

o Motor Enclosure: The motor enclosure must be suitable for the conditions of

service.

o Electrical Hook-up: The electrical connections to the motor should be performed by

a certified electrician. It is critical that the supply voltage match the motor

nameplate voltage or serious motor damage or fire can result.



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o Priming & Direction of Rotation: Prime the pump and then brief ly jog the motor to

assure proper motor direction. Motor shaft direction must be counter-clockwise as

seen from the pump end

o Saf ety: Never operate pump without all saf ety devices installed.

10.0 Troubleshooting

Often the root causes of f ailure are the same but the symptoms are diff erent. A little care

when first symptoms of a problem appear can save the pumps from permanent f ailures. The

f acts of f ailures mostly encountered are design errors, poor operation and poor

maintenance practices. Below are the typical problem and solutions:

Problem Possible Cause Corrective Action

No discharge

Pump notprimed

y Verif y suction pipe is submerged

y Increase suction pressure

y Open suction valve

Wrong direction of rotation y Reverse motor leads

Valves closed y Open all suction and discharge valvesBypass valve open y Close bypass valve

Air leak in suction line

y Tighten connections

y Apply sealant to all threads


Clogged strainer y Clean strainer

Clogged impeller y Disassemble and remove blockage

Impeller greatly worn or

damaged y Disassemble and replace impeller

Insufficient

discharge

Suction pressure too low

y Increase suction pressure

y Verif y suction piping is not too long

y Fully open and suction valvesBypass valve open y Close bypass valve

Partly clogged strainer y Clean strainer

Partly clogged impeller y Disassemble and remove blockage

Speed too low y Increase driver speed if possible

y Use larger size pump if required

Impeller worn or damaged Disassemble and replace impeller

Loss of suction after

satisf actory

operation

Pump not properly primed y Re-prime pump

Air leaks in suction line

y Tighten connections

y Apply sealant to all threads


Air or vapour pockets in

suction liney

Rearrange piping as necessary

Increase in f luid viscosityy Heat f luid to reduce viscosity

y Reduce pump speed

Excessive power

consumption

Fluid viscosity higher than

specified

y Heat f luid to reduce viscosity

y Reduce pump speed

y Increase driver horsepower

Liquid specific gravity higher

than expected

y Reduce pump speed

y Increase driver horsepower



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Total head greater than

specified

y Increase pipe diameter

y Decrease pipe run

Total head lower than

specified, pumping higher

f low than expected

y Install throttle valve

Total head higher than rating

with f low at rating y Install impeller with correct diameter

Rotating parts binding or

severely worn y Disassemble and replace worn parts

Rapid pump wear

Abrasives in f luid

y Install suction strainer

y Limit solids concentration

y Reduce pump speed or use larger

pump running at lower speed

Corrosion wear

y Use materials of construction that

are acceptable for f luid being

pumped

Extended dry running y Install power sensor to stop pump

Discharge too high

y Increase pipe diameter

y Decrease pipe run

Excessive noise and

vibration

Partly clogged impeller

causing imbalancey Disassemble and remove blockage

Damaged impeller and/or

shaft

y Disassemble and replace damaged

parts

Base not rigid enough

y Tighten hold-down bolts on pump

and motor or ad just stilts

y Inspect grout and reground if

necessary

Worn pump bearings y Replace bearings

Worn motor bearings y Replace bearings or motor

Pump cavitations y Increase NPSH available

Excessive product

leakage

Static seal f ailure caused by

chemical incompatibility or

thermal breakdown

y Use O-ring or gaskets made of

material compatible with f luid and

temperature of the application

Static seal f ailure caused by

improper installation

y Install O-ring or gaskets without

twisting or bending

y Use star-pattern torque sequence

non house bolts during assembly

y Allow Tef lon O-ring to cold f low and

seat during tightening

y Torque bolts to specification

Pump port connections not properly sealed

y Use Tef lon tape or other suitable

sealant y Use gasket compatible with f luid and

temperature of the application

Crevice corrosion of pump

housing material

y Only pump chemicals that are

compatible with the pump housing

material

y Decrease temperature to reduce

corrosion rate to acceptable value

y Flush idle pumps that are used to



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ump corrosive chemicals

y Eliminate contaminants in the f luid

that can accelerate corrosion wear

11.0 Pump Enquiry Information

To ensure the correct pump is selected for typical application, the following details are required.

There details required for all applications Additional details is liquid is not water

y Flow rate required

y Static suction head

y Suction pipe inside diameter

y Foot valve or open pipe

y Suction pipe length & material

y Discharge pipe inside diameter

y Discharge pipe length & material

y Temperature

y Detail of solids

y Height above sea level

y Detail of application

y NPSH

y Service Liquid

o Additional requirements

o Sprinklers or other pressure

requirement

o Future expansion, etc

y Full liquid description

y Specific gravity

y Viscosity

y pH value

y other details or data sheet

For all applications advise

y Driver requirements:

o Electric voltage/phase/Hz

o Electric hazardous location o Diesel pref erences

o Petrol pref erences

o Hydraulic system available

*Table for service liquid are shown at Appendix B



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Appendix A Types of Pump and Basic Components

Fig 1: schematic design for PDP

a) Reciprocating piston pump

b) External gear pump

c) Double-screw pump

d) Sliding vane

e) Three-lobe pump

f)

Double circumf erential piston g) Flexible-tube squeegee



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Fig 4: Typical pump assembly

Fig 5: Open impeller



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Fig 6: Closed impeller



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Appendix B Service Liquid



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group maintenance - pump

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