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Q&A
Flowserve Corporation Property and Confidential 39
Understanding Head and Pressure
Centrifugal Pump Basics
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Understanding Head and Pressure
Centrifugal Pump Basics
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Shows the relationship between head and pressure.
Specific Gravity’s Effect on Head
Centrifugal Pump Basics
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Understanding Head and Flow
Centrifugal Pump Basics
Head is found in the following forms:
• Static Pressure Head
• Dynamic Velocity Head
• Static Elevation Head
• Friction Head
Flowserve Corporation Property and Confidential
Centrifugal Pump Basics
System Head
Head Capacity
Desired Head
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System Curve
Desired
Flowrate
-Static Head
-Pressure Head
-Friction and
Other Losses
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System Head
Centrifugal Pump Basics
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Centrifugal Pump Basics
System Head
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Centrifugal Pump Basics
Velocity
Where:
GPM = flow rate
=
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Veloci ty Head
Centrifugal Pump Basics
• Is the energy of a liquid as a result of its motion at a velocity
• Equivalent head in feet that the liquid would have to fall to acquire
the same velocity
Flowserve Corporation Property and Confidential 48
Where:
hv = velocity head
v = velocity
g = gravity (32.2 ft/s2 or 9.81 m/s2)
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Friction Head and Friction Losses
Centrifugal Pump Basics
•Pressure, converted to head, needed to overcome resistance to flow of
a liquid in a piping system
•Resistance:
o Pipe friction
o Valves, fittings
Flowserve Corporation Property and Confidential
o Heat exchangers
o Filters, orifices, etc.
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Centrifugal Pump Basics
Friction Head and Friction Losses
Values in feet of water can be found in the Hydraulic Institute pipe
friction manual and other technical manuals.
Where:
Flowserve Corporation Property and Confidential 50
hf = fiction head, feet or meters
K = coefficient for the valves and fittings
g = gravitational constant, 32.2 ft/s2 or 9.81 m/s2
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Centrifugal Pump Basics
Friction Head and Friction Losses
Friction head is determined by the equations:
Where:
f = friction factor V = velocit in ft/sec
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L = pipe length (feet)
D = pipe ID (feet)
K = coefficient for the
valve/fitting
Friction
Centrifugal Pump Basics
• Viscosity
• Size of pipe
• Roughness of pipe’s interior wall
• Age condition of pipe material
Flowserve Corporation Property and Confidential
• Total length of pipe
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Centrifugal Pump Basics
Friction Head Loss for
Water per 100 ft of Pipe
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Centrifugal Pump Basics
Friction Head Loss for
Water per 100 ft of Pipe
Notice the difference in
head loss between a one
inch line and a two inch
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line at the same flow rate.
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Centrifugal Pump Basics
Resistance Coeffic ients (K) Values
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Centrifugal Pump Basics
Losses Due to Friction
Pipe and fitting condition will have an impact on losses.
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Centrifugal Pump Basics
Friction Head and System Changes
For constant pipe diameter
•Friction loss will vary as the square of the capacity ratio. If capacity is
doubled, friction loss will increase 4 times. Capacity varies as the square
root of the total head.
•Doubling the head will increase capacity 1.41 times.
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Centrifugal Pump Basics
Friction Head and System Changes
For constant capacity
•Friction loss is inversely proportional to the 5th power of the pipe
diameter.
•Reducing pipe size by 50% will increase friction loss 32 times.
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Centrifugal Pump Basics
Total Discharge Head and Total Suct ion Head
These total heads can be calculated using the following equations:
total di scharge head discharge surface pressure
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static discharge head discharge friction head
Total Discharge Head and Total Suct ion Head
Centrifugal Pump Basics
total suction head suction surface pressure
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suction static head suction friction head
Note:
The three contributing heads must have been converted previously to feet of
liquid before the above equations can be solved.
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Calculating System Head
Centrifugal Pump Basics
Total Head is the difference between the total discharge head and total
suction head.
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hd and hs must be expressed in the same units
Q&A
Flowserve Corporation Property and Confidential 62
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