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PUMP

Pump is a mechanical device that converts mechanical power into hydraulic energy.

Function of Pump:

Pump enables a liquid to:

. Flow from a region or low pressure to one of high pressure

. Flow from a low level to a higher level

. Flow at a faster rate

Applications:• Drainage System• Agriculture and Irrigation system• Tube wells• Oil pumps

Types of Pump

There are two main categories of pump• Dynamic Pressure Pumps.• Positive Displacement Pumps.

Difference between dynamic pressure and positive displacement pump:• Dynamic pump imparts velocity energy to the fluid, which is converted to

pressure energy upon exiting the pump casing

• Positive displacement pump moves a fixed volume of fluid within the pump casing by applying a force to moveable boundaries containing the

fluid volume.

Positive Displacement Pump Dynamic Pressure Pump

Classification of Pumps

Diaphragm

Piston

Plunger

Reciprocating Rotary

Mixed flow Gear

Lobe

Sliding Vane

Screw

Axial flow

Centrifugal

Dynamic Pressure Pump

Turbine

Positive Displacement

PUMP

Parameters for the Selection of Pump

Some of the parameters that decide the selection of pump are:

• Pressure and capacity of liquid being handled

• Speed of rotation and power requirement

• Properties such as viscosity, corrosiveness etc of fluid

• Availability of space for positioning of pump

• Initial and maintenance cost

Parameters for the Selection of PumpParameter Centrifugal

PumpsReciprocating Pumps

Rotary Pumps

Optimum Flow and Pressure Applications

Medium/High Capacity,

Low/Medium Pressure

Low Capacity,High Pressure

Low/Medium Capacity,

Low/Medium Pressure

Maximum Flow Rate

100,000+ GPM 10,000+ GPM 10,000+ GPM

Maximum Pressure 6,000+ PSI 100,000+ PSI 4,000+ PSI

Space Considerations

Requires Less Space

Requires More Space Requires Less Space

Costs Lower InitialLower

MaintenanceHigher Power

Higher InitialHigher Maintenance

Lower Power

Lower InitialLower

MaintenanceLower Power

Centrifugal Pumps

Centrifugal Pump can be defined as a mechanical device used to transfer

liquid

• Converts the energy provided by a prime mover, such as an electric motor,

steam turbine or gasoline engine to energy within the liquid being pumped

Working of Centrifugal Pump

Centrifugal pumps works on principle of centrifugal force.• It has a rotating impeller also known as a blade that is immersed in the

liquid. • Liquid enters the pump near the axis of the impeller and the rotating

impeller sweeps the liquid out toward the ends of the impeller blades at high pressure.

Components of Centrifugal Pump

1. Impeller

2. Casing

3. Drive Mechanism

4. Pump Shaft


1. Impeller is a rotating component of a centrifugal pump which transfers energy from the motor that drives the pump to the fluid being pumped.

• Thicker the impeller - More fluid• Larger the diameter - More pressure• Increase the speed - More water and pressure

“Eye of the Impeller”Water Entrance

Diameter of the Impeller

Thickness of the impeller

Components of Pump

Impeller is classified into three types depending upon impeller vanes• Forward Vanes: Vanes are in the direction of motion of impeller• Backward Vanes: Vanes are opposite to the direction of motion of

impeller• Radial Vanes: Vanes are straight

Radial vanes Backward vanes Forward vanes


2. Casing is a stationary part of the pump that receives the fluid being pump by the impellerCasing generally are two types:• Volute Casing: It is used for a higher head. A volute is a curved funnel increasing in area to the discharge port.• Circular Casing: It is used for low head and high capacity. It has stationary diffusion vanes surrounding the impeller periphery that convert velocity energy to pressure energy. Volute

SuctionImpeller


3. Drive Mechanism provides energy to the impeller. It can be electric

motor ,steam engine or gasoline engine.

4. Pump Shaft transmits power from prime mover to the pump impeller.

Pump ConfigurationPump may be connected in series or parallel.

1. Series Pump Pump is said to be connected in series if the discharge of one pump is connected to the suction side of a second pump.

It produces same flow rate but higher head.

Pump Configuration

2. Parallel PumpTwo or more pumps are connected to a common discharge line, and share the same suction conditions

It produces same head but high flow rate.

Affinity Law

Affinity Law of centrifugal pump indicates the influence on flow rate, head

and power consumption of a pump due to:

change in impeller speed

change in impeller diameter

• Flow changes directly as a change in speed or diameter

Q a N• Head changes as the square of a change in speed or diameter

H a N2

• Horsepower changes as the cube of a change in speed or diameter

W a N3

Performance Characteristic Curve

• Predict the performance of pump when the pump is working under

different flow rate.

Terminologies Used in Pump

Head is defined as height of water column.

OR

Head is the height at which a pump can raise water up


• Static Suction Head is head on the suction side, with pump off.• Static Discharge Head is head on discharge side of pump, with the pump

off.• Dynamic Suction Head is head on suction side of pump with pump on.• Dynamic Discharge Head is head on discharge side of pump with pump

on.


• Pressure Head is measure of fluid’s potential energy.

• Velocity Head is measure of fluid’s kinetic energy.

• Friction Head is measure of energy loss that heats fluid.

• Net Positive Suction Head (NPSH) defines the pressure required at the

suction of a pump to prevent cavitation

• Manometric Head is defined as the change in total energy head produced

by the pump when fluid moves through it.

Losses and Efficiencies

1. Hydraulic Efficiency are the losses the occur between the suction and the delivery ends of a pump.

Hydraulic efficiency varies from 0.6 to 0.9.

2. Volumetric efficiency is the ratio of the actual discharge to the total

discharge. Q = Amount of discharge

∆Q = Amount of leakage.

It’s value lies between 0.97 and 0.98

3. Mechanical efficiency is the ratio of the actual power input to the impeller and the power given to the shaft.

m P = Total power input to the shaft

∆ P = Mechanical losses

It’s value lies between 95% - 98%.

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Losses and Efficiencies

4. Overall Efficiency is the ratio of the total head developed by a pump to the total power input to the shaft.

Range of overall efficiency is between 0.71 to 0.86.

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Sizing of Pump

To size a pump, you must define:• Flow rate of liquid the pump is required to deliver• Total differential head the pump must generate to deliver the required flow

rate

• Flow RateDetermined by the process in which the pump is installed.

Defined by the mass and energy balance of the process.

• Total Differential HeadThe total differential head is made up of 2 components.

Total differential head = static head difference + frictional head losses

Sizing of Pump

• Static Head DifferenceDifference in head between the discharge static head and the suction static

head. Static head difference = discharge static head – suction static head

Sizing of Pump

• Suction Static HeadThe suction static head is sum of the gas pressure at the surface of the liquid in the suction vessel and the difference in elevation between the surface of the liquid in the suction vessel and the center line of the pump.

Suction static head = Suction vessel gas pressure head + elevation of suction vessel

liquid surface – elevation of pump center line

Sizing of Pump

• Discharge Static Head Discharge static head = Discharge vessel gas pressure head + elevation of

discharge pipe outlet – elevation of pump center line

The discharge pipe outlet may be above the surface of the liquid in the discharge vessel or it may be submerged as shown in these two diagrams.

Sizing of Pump

• Frictional Head Losses The frictional head losses are usually calculated from the Darcy-Weisbach equation using friction factors and fittings factors to calculate the pressure loss in pipes and fittings.

Frictional head losses = frictional losses in suction piping system + frictional

losses in discharge piping system

Sizing of Pump

• Net Positive Suction Head AvailableNet positive suction head available (NPSHa) must exceed the net positive suction head required (NPSHr) for that particular pump.

NPSHr is given by the pump manufacturer Net positive suction head available = absolute pressure head at the pump

suction – liquid vapor pressure head

• Pump PowerPumps are usually driven by electric motors, diesel engines or steam

turbines. Determining the power required is essential to sizing the pump driver. Pump power = flow rate x total differential head x liquid density x acceleration

due to gravity / pump efficiency

Sizing of PumpExample:Water Flow Rate:30000 kg/hr

Water Temperature:20C

Water Density :998 kg/m3

Vapor Pressure :0.023bara

Water Viscosity:1cP

Pump efficiency is 70%

Calculation:

Pump Problems and Troubleshooting

• Cavitation Cavitation occurs when the pressure falls below the vapor pressure of the liquid at a given temperature, small bubbles of vapor are formed.

Vapors implode when they are transported to an area of high pressure


Mechanism of Cavitation


Damage to Pump Parts


• Priming

Priming is the process of filling the impeller of centrifugal pump with water.• Required when there is a first start up.• Pump casing becomes filled with vapors or gases, the pump impeller

becomes gas-bound and incapable of pumping.


References

• “Pump Wisdom” by Heinz . P . Bloch

• “Improving Pumping System Performance” A Source Book for Industry-

2nd Edition

• “Centrifugal Pump Design and Applications” 2nd Edition

Documents

Pump old