pump head presentation(pdf)
TRANSCRIPT
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PUMP HEADUnderstanding pump head and NPSH
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200722120
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Contents 1. Pump head Head Suction head, Discharge head
Total head
Friction head
Operating point
2. NPSH
Cavitation
NPSH
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Head
The height at which a pump can raise water up.
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Head
The height at which a pump can raise water up.
Head is affected by suction condition.
: Head is proportional to suction level
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Head
Capacity to do a job. (Compared in the same suction level)
Independent of the type of fluid.
(When viscosity is relatively low and similar to water)
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Head
H = 2.31 p SG
H : head(ft)
P : pressure(psi)
SG : Specific gravity of fluid being pumped
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Suction head, Discharge head
Suction head
: vertical distance between the pump datum and the
liquid surface in suction well.
Discharge head
: vertical distance between the pump datum point and
the liquid surface in the receiving tank. (or Discharge
pipe)
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Suction head, Discharge head
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Total head
Vertical distance between the level of the source of the
supply and the surface of the discharge liquid.
Manufacturers use this term to show the performance of
their product.
Total head = Discharge headSuction head
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Total head
When the liquid level is below the pump datum, then
suction head has a negative value.
In the case, suction head is also called suction lift.
Total head = Hd + Hs
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Friction headloss of head that occurs in pipe flow due to viscous effect.
No flow With flow
Total head = HdHs + Friction head
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Operating point
Performance curve: total head vs flow
System curve: total of friction head losses vs flow
Operating point: The point where two curves intersect.
: Pump cannot work without adjusting
system.
: Pump capacity is bigger than system
requirement
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Cavitation
Formation of gas bubbles
in a flowing liquid.
Occurs when the pressurein the pump inlet drops
below the vapor pressure
of the liquid.
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Cavitation
Loud noise
Loss of capacity
Damage
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NPSH
Net Positive Suction Head.
Must be calculated before using pump to prevent
cavitation.
NPSHa and NPSHr
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NPSHr and NPSHa
NPSHr
Required
Minimum pressurerequired at the suction
port of the pump to keep
the pump from cavitating.
Depends on the pump.
Given.
NPSHa
Available
Absolute pressure at thesuction port of the pump.
Depends on the system.
CALCULATE.
NPSHa > NPSHr 1.3
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NPSHa : calculation
NPSHa = Ha HzHfHvp
Term Definition
Ha Absolute pressure on the surface of the liquid in the supply tank
Hz Vertical distance between the surface of the liquid in the supply tank
and the centerline of the pump
Hf Friction losses in the suction piping(Values can be found at the friction chart)
Hvp Absolute vapor pressure of the liquid at the pumping temperature
(Liquid types and temperature of the system should be considered)
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NPSHa : example & selection of pump
GivenHa : 10m
Hz : 3m
Hvp : 0.2m
Hf : 0.5m
NPSHa = 10+3-0.2-0.5
= 6.3
6.3 / 1.3 = 4.85
Thus, we need a pump withthe NPSHr smaller than 4.85