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Bellevue Moses Lake Canby
http://www.Pumptechnw.com
Joe Evans, Ph.D
Pump Ed 101
Centrifugal Pump Hydraulics
Three Reasons BEP Operation is Important
Joe Evans, Ph.D
http://www.PumpEd101.com
Pump ED 101
Centrifugal Pumps
Animated Software Company
Pump ED 101
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Displacement
Impellers
Pump ED 101 Dynamics
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Centrifugal Pump Dynamics
Discharge
Volute
Impeller
Suction
What Type of Energy is Added by the Impeller ?
Pump ED 101
Hint *
Dynamics
Centrifugal
Cutwater
Centrifugal Force
It is defined as “center fleeing”
Pump ED 101 Dynamics
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Centrifugal Force
When an object is traveling in a circle, it is actually moving in a straight line at any single point in time.
Instead it actually moves in the same direction it was traveling at the exact instant it is released.
Farce
Pump ED 101
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Dynamics
So, How Does It Work ?
1 Rotation of the impeller forces water from its entry point, at the eye, into its vanes.
2 Water moving through the vanes creates a partial vacuum at the eye allowing atmospheric, or some other outside pressure, to force more water into the eye.
3 As water travels through the vanes, it gains rotational velocity (kinetic energy) and reaches its maximum velocity just as it exits the vanes.
4 Upon exiting the vanes, water enters the volute where most of its kinetic energy of motion is transformed into pressure energy.
Pump ED 101
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Dynamics
The Volute and its Function
The volute houses the impeller and is the “receptacle” for the water exiting its vanes.
Its smooth, nearly circular, geometry guides the flow from the impeller towards its discharge. During this trip, the flow encounters an ever increasing volume.
The volute converts the kinetic energy (velocity) imparted by the impeller into pressure.
Pump ED 101
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Dynamics
The Performance Curve
Pump Information
Flow and Pressure at Several Points
Hydraulic Efficiency
Horsepower
Net Positive Suction Head Required (NPSHr)
Pump ED 101
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Curve
Pump ED 101
The Performance Curve
Pump ED 101
The Performance Curve
BEP
11.5”
Pump ED 101
The Performance Curve
BEBOP
The Performance Curve
Pump ED 101
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Curve
BEBOP
BEBOP & The Cost of Pump Operation
Power consumption is at its lowest
Maintenance costs are their lowest
Useful life is at its maximum
Pump ED 101
When a centrifugal pump is operated at BEBOP
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Head (
ft)
Gallons Per Minute
System Curve Design Flow
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300' 6" Steel Pipe
Pump ED 101
The System Curve
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105
95
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72
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57
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121
105
95
87
79
72
65
57
49
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Head (
ft)
Gallons Per Minute
Simplex Duplex
System Curve Design Flow
H4HX 1750 RPM, Trim 10", 71% eff
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300' 6" Steel Pipe
Pump ED 101
The System Curve
13.8 HP
24.4 HP
109
93
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109
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83
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66
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37
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0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700
He
ad
(ft
)
Gallons Per Minute
Simplex Duplex System Curve Design Flow
H4HX 1750 RPM, Trim 9.5", 71% eff
•
300' 8" Steel Pipe
Pump ED 101
The System Curve
11.5 HP
22.2 HP
System Hydraulics – Radial Thrust
Ideally a pump should operate between 90% and 110% of its BEBOP.
If it does not, the radial forces that act upon a centrifugal pump’s impeller can account for a large percentage of premature failures.
The increased shaft deflection will decrease mechanical seal, wear ring, and bearing life.
Worse case - shaft breakage
19 Pump Ed 101
• Forms about the periphery of the impeller due to uneven volute geometry
• A function of total head, width and diameter of the impeller
• Usually reaches a maximum at or near shut off head
Radial Thrust
Pump Ed 101
Pump ED 101
Radial Thrust Factor
Pump ED 101
Radial Thrust Calculator
Pump ED 101
Cavitation
Pump ED 101
Types of Cavitation
Normal Cavitation – Low NPSHa
Wear Ring Recirculation – Low Flow
Discharge Recirculation – Low Flow
Suction Recirculation – Low Flow
Pump ED 101
Types of Cavitation
Pump ED 101
Wear Ring Recirculation
Cavitation
Pump ED 101
Discharge Recirculation Cavitation
Occurs on the high pressure side of the vane
Pump ED 101
Discharge Recirculation Cavitation Two Vane
Pump ED 101
Suction Recirculation Cavitation
Occurs on the high pressure side of the vane
Pump ED 101
Suction Recirculation Cavitation
Pump ED 101
Suction & Discharge Recirculation Cavitation
Conservation of Energy
50 PSI 50 PSI 48 PSI
100 GPM
Pump ED 101
Bernoulli’s theorem states that, during steady flow, the energy at any point in a conduit is the sum of the velocity head, pressure head, and elevation head. It also states that this sum will remain constant if there are no losses. Daniel Bernoulli 1700-1782
H = v + p + z = Constant
*
Dynamics
Pump ED 101 Total Head
Total Suction Head hs = ± hgs + hvs ± Zs
Total Discharge Head hd = hgd + hvd ± Zd
Total Dynamic Head H = hd - hs
Total Dynamic Head
Where:
hg = gauge head
hv = velocity head
Z = gauge distance above or below datum
Where:
hd = discharge head
hs = suction head
Pump ED 101
*
Dynamics
What is Velocity Head ?
It is a form of energy that cannot be measured with a pressure gauge.
Why is It Important ?
If it is not measured, pump test results will be inaccurate.
Pump ED 101
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Dynamics
Piezometer Measurement
Energy = v + P + z = Constant
Pump ED 101
*
Dynamics
Piezometer & Pitot Tube Measurement
Energy = v + P + z = Constant
3X4 End Suction - 650 GPM
Pump ED 101 Total Head
Pump Testing
hv = V2 / 2g
258.3 ’ 247.2 ’
Actual Pressure = 112.5 PSI (260 ft)
TDH Error 4.7%
TDH Error 0.6%
Velocity 3” = 28.2 ft/sec Velocity 5” = 10.4 ft/sec
3” Section hv = 12.4 ft 5” Section hv = 1.7 ft
At 50 PSI 11% Error
Pump Ed 101
Centrifugal Pump Hydraulics
Three Reasons BEP Operation is Important
Joe Evans, Ph.D
http://www.PumpEd101.com
Pump ED 101
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