Chapter 5
Centrifugal Pump Concept
Think of a sprinkler head, except you turn the
sprinkler to move the water rather then the
other way around
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• Principle of angular
momentum
conservation
• Momentum=mass*vel
ocity
• Angular
momentum=radius*ma
ss*velocity
• Torque=time rate of
change of angular
momentum
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PUMPING ENERGY
• Power=Qhpump
• = Q (P2-P1)
• The mechanical
horsepower, also
known as imperial
horsepower, of exactly
550 foot-pounds per
second is
approximately
equivalent to 745.7
watts.
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Types of Pumps
• Propeller, used for low
head (<12 m), high
capacity (>20L/s)
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Multistage propeller
• Used in deep wells
with high head and low
flow rate
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Jet Pumps
• Take energy from high
pressure fluid
• No moving parts
• Compact and light but
not efficient
• Q1 is high pressure
fluid
• Q2 is fluid to be
pumped
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Positive Displacement Pumps
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Positive Displacement Pump
• Very high head, low flow
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How to size a pump
• To find operating point:
• obtain pump curve from manufacturer, pumps pump
less water at higher heads
• calculate the system curve, the system curve is an
equation that tells how much water flows through a
pipe system as a function of the head (energy per
unit weight) added by the pump.
•
• Energy efficiency is maximized when the operation
point (intersection of pump and system curves) is at
the point of maximum pump efficiency
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Cavitation is Evil
• Cavitation can occur whenever the absolute
pressure locally gets below the vapor
pressure of the water
• Frequent issue when pump is higher than
water reservoir but can occur with any
pump
• Common site of cavitation is near tips of
impellor vanes where velocity is high
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Pump Selection
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Pump Tips
• http://www.pumpfundamentals.com/centrifu
gal-pump-tips.htm
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Pump Fundamentals
• http://www.pumpfundamentals.com/tutorial2
.htm#pump-pressure
• http://www.pumpworld.com/Capacity.htm
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How to size a pump
• To find operating point:
• obtain pump curve from manufacturer, pumps pump
less water at higher heads
• calculate the system curve, the system curve is an
equation that tells how much water flows through a
pipe system as a function of the head (energy per
unit weight) added by the pump.
•
• Energy efficiency is maximized when the operation
point (intersection of pump and system curves) is at
the point of maximum pump efficiency
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Explain Pump Curve
Brake horsepower (bhp) is the
measure of an engine's horsepower
before the loss in power caused by the
gearbox, alternator, differential, water
pump, and other auxiliary components
System curve
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How to size a pump
• To find operating point:
• obtain pump curve from manufacturer, pumps pump
less water at higher heads
• calculate the system curve, the system curve is an
equation that tells how much water flows through a
pipe system as a function of the head (energy per
unit weight) added by the pump.
•
• Energy efficiency is maximized when the operation
point (intersection of pump and system curves) is at
the point of maximum pump efficiency
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Example System
• Show using Bernoulli Equation (good quiz!)
• Hpump=z2-z1+hloss
• This is the system curve for our simple
system shown below
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Solution where curves intersect
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Pumps in Parallel – Add Discharge
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Pumps in Series – Add Head
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The solid lines are labeled; the dashed line is the system curve. If we change the
pump rpm (revolutions per minute), from 3250 to 4350, how much more water do we
pump and how does the power input change? Show your work by drawing on the
figure.
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