Centrifugal pump lecture 1

2
Introduction
What are Pumping Systems
Objective of pumping system
(US DOE, 2001)
• Transfer liquid
from source to
destination
• Circulate liquid
around a system

3
Introduction
What are Pumping Systems
• 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

4
Introduction
Pumping System Characteristics
• Head
• Resistance of the system
• Two types: static and friction
• Static head
• Difference in height between
source and destination
• Independent of flow
destination
source
Stati
c
head
Static
head
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
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
Friction
head
(no static head)
Flow

8
Introduction
In most cases:
Total head = Static head + friction head
System
head
Static head
Flow
Friction
head
System
curve
System
head
Static head
Flow
Friction
head
System
curve

9
Type of Pumps
Pump Classification
Classified by operating principle
Dynamic
Positive
Displacement
Pumps
Centrifugal Special effect Rotary Reciprocating
Internal
gear
External
gear
Lobe
Slide
vane
Others (e.g.
Impulse, Buoyancy)

10
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

16
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

Centrifugal 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 Impellers
Diameter of
the Impeller
Thickness
of the impeller
Impeller
Vanes
“Eye of the
Impeller”
Water
Entrance
• Thicker the Impeller- More Water
• Larger the DIAMETER - More Pressure
• Increase the Speed - More Water and Pressure

Two Impellers in Series
Direction of Flow
• Twice the pressure
• Same amount of water

Multiple Impellers in Series
Direction of Flow Direction of Flow
• Placing impellers in series increases the amount of head
produced
• The head produced = # of impellers x head of one impeller

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

Step #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

Step #2, Vertical Axis
• The head the pump produces is plotted
on the vertical axis (Y axis)
• Usually express in Feet of Water
Pump Flow Rate
Head

Step #3, Mapping the Flow and the Head
• Most pump
performance curves
slope from left to
right
Pump Flow Rate
Performance Curve
Head

Important Points
• Shut-off Head is the maximum pressure or
head the pump can produce
• No flow is produced
Pump Flow Rate
Head
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 Curve
Step #1, Horizontal Axis
• The System's flow rate in plotted on the horizontal axis ( X
axis)
• Usually expressed in Gallons per Minute
System Flow Rate

Step #2, Vertical Axis
 The head the system requires is plotted on the
vertical axis (Y axis)
 Usually express in Feet of Water
Pump Flow Rate
Head

Step #3, Curve Mapping
• The friction loss is mapped onto the graph
• The amount of friction loss varies with flow through the
system
Head
Pump Flow Rate
Friction Loss

Head
The point on the system curve that intersects
the pump curve is known as the operating
point.
Pump Flow Rate

Head
PUMP SELECTION
Pump Flow Rate
Valve Open
Valve Partially Open
Valve Barely Open

Centrifugal pump lecture 1

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Centrifugal pump lecture 1