CENTRIFUGAL PUMP

2

Introduction

Objective of pumping system

What are Pumping Systems

(US DOE, 2001)

• Transfer liquid

from source to

destination

• Circulate liquid

around a system

3

Introduction

• Main pump components

• Pumps

• Prime movers: electric motors, diesel engines,

air system

• Piping to carry fluid

• Valves to control flow in system

• Other fittings, control, instrumentation

• End-use equipment

• Heat exchangers, tanks, hydraulic machines

What are Pumping Systems

4

Introduction

• Head

• Resistance of the system

• Two types: static and friction

• Static head

• Difference in height between

source and destination

• Independent of flow

Pumping System Characteristics

destination

source

Stati

c

head

Statichead

Flow

5

Introduction

• Static head consists of

• Static suction head (hS): lifting liquid relative to

pump center line

• Static discharge head (hD) vertical distance

between centerline and liquid surface in

destination tank

• Static head at certain pressure

Pumping System Characteristics

Head (in feet) = Pressure (psi) X 2.31

Specific gravity

Conversion Factors Between Head and Pressure

• Head (feet of liquid) =Pressure in PSI x 2.31 / Sp. Gr.

• Pressure in PSI = Head (in feet) x Sp. Gr. / 2.31

• PSI is Pounds per Square Inch

• Sp. Gr. is Specific Gravity which for water is equal to 1

– For a fluid more dense than water, Sp. Gr. is greater than 1

– For a fluid less dense than water, Sp. Gr. is less than 1

7

Introduction

• Friction head

• Resistance to flow in pipe and fittings

• Depends on size, pipes, pipe fittings, flow

rate, nature of liquid

• Proportional to square of flow rate

• Closed loop system

only has friction head

(no static head)

Pumping System Characteristics

Frictionhead

Flow

8

Introduction

In most cases:

Total head = Static head + friction head

Pumping System Characteristics

Systemhead

Flow

Static head

Frictionhead

Systemcurve

System head

Flow

Static head

Frictionhead

Systemcurve

9

Type of Pumps

Classified by operating principle

Pump Classification

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gearLobe

Slide

vane

Others (e.g.

Impulse, Buoyancy)

Pumps

DynamicPositive

Displacement

Centrifugal Special effect Rotary Reciprocating

Internal

gear

External

gearLobe

Slide

vane

Others (e.g.

Impulse, Buoyancy)

Pumps

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Type of Pumps

Positive Displacement Pumps

• For each pump revolution

• Fixed amount of liquid taken from one end

• Positively discharged at other end

• If pipe blocked

• Pressure rises

• Can damage pump

• Used for pumping fluids other than

water

11

Type of Pumps

Positive Displacement Pumps

• Reciprocating pump

• Displacement by reciprocation of piston

plunger

• Used only for viscous fluids and oil wells

• Rotary pump

• Displacement by rotary action of gear, cam

or vanes

• Several sub-types

• Used for special services in industry

Centrifugal Pumps

A machine for moving fluid by accelerating the fluid RADIALLY outward.

A collection chamber in the casing converts much of the Kinetic Energy (energy due to velocity) into Head or Pressure.

14

Centrifugal Pumps

How do they work?

(Sahdev M)

• Liquid forced into

impeller

• Vanes pass kinetic

energy to liquid: liquid

rotates and leaves

impeller

• Volute casing converts

kinetic energy into

pressure energy

Type of Pumps

Centrifugal Pumps

Impeller Sahdev)

• Main rotating part that provides centrifugal

acceleration to the fluid

• Number of impellers = number of pump stages

• Impeller classification: direction of flow, suction type

and shape/mechanical construction

Shaft

• Transfers torque from motor to impeller during pump

start up and operation

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Type of Pumps

Centrifugal Pumps

Casings

Volute Casing (Sahdev)• Functions

• Enclose impeller as “pressure vessel”

• Support and bearing for shaft and impeller

• Volute case

• Impellers inside casings

• Balances hydraulic pressure on pump shaft

• Circular casing

• Vanes surrounds impeller

• Used for multi-stage pumps

• This machine consists of an IMPELLER rotating within a case (diffuser)

• Liquid directed into the center of the rotating impeller is picked up by the impeller’s vanes and accelerated to a higher velocity by the rotation of the impeller and discharged by centrifugal force into the case (diffuser).

Centrifugal Pumps

Diameter of the Impeller

Thicknessof the impeller

Centrifugal Impellers

• Thicker the Impeller- More Water

• Larger the DIAMETER - More Pressure

• Increase the Speed - More Water and Pressure

Impeller Vanes

“Eye of the Impeller”Water Entrance

Impellers

Two Impellers in Series

Direction of Flow

• Twice the pressure• Same amount of water

Multiple Impellers in Series

• Placing impellers in series increases the amount of head produced

• The head produced = # of impellers x head of one impeller

Direction of Flow Direction of Flow

Pump Performance Curve

• A mapping or graphing of the pump's ability to produce head and flow

Pump Performance CurveStep #1, Horizontal Axis

• The pump's flow rate is plotted on the horizontal axis ( X axis)

• Usually expressed in Gallons per Minute

Pump Flow Rate

Pump Performance CurveStep #2, Vertical Axis

Pump Flow Rate

• The head the pump produces is plotted on the vertical axis (Y axis)

• Usually express in Feet of Water

Hea

d

Pump Performance CurveStep #3, Mapping the Flow and the Head

Pump Flow Rate

• Most pump performance curves slope from left to right

Performance Curve

Hea

d

Pump Performance CurveImportant Points

• Shut-off Head is the maximum pressure or head the pump can produce

• No flow is produced

Pump Flow Rate

Hea

d

Shut-off Head

System Performance Curves

• System Performance Curve is a mapping of the head required to produce flow in a given system

• A system includes all the pipe, fittings and devices the fluid must flow through, and represents the friction loss the fluid experiences

System Performance CurveStep #1, Horizontal Axis

System Flow Rate

• The System's flow rate in plotted on the horizontal axis ( X axis)

• Usually expressed in Gallons per Minute

System Performance CurveStep #2, Vertical Axis

Pump Flow Rate

The head the system requires is plotted on the vertical axis (Y axis)

Usually express in Feet of Water

Hea

d

System Performance CurveStep #3, Curve Mapping

• The friction loss is mapped onto the graph

• The amount of friction loss varies with flow through the system

Hea

d

Pump Flow Rate

Friction Loss

Hea

d

Pump Flow Rate

The point on the system curve that intersects

the pump curve is known as the operating

point.

Hea

d

Pump Flow Rate

PUMP SELECTION

Valve Open

Valve Partially Open

Valve Barely Open

Thank You