Why head gain decreases with increase in flow rate of pump?
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The head of a pump is the differential head between the suction and discharge sides (head required for the pump to deliver).
Differential head = Differential pressure / ρ g
Differential pressure = Discharge pressure - suction pressure
Discharge pressure = Static discharge pressure + pipe pressure drop (discharge side) + fitting pressure drop (discharge side)
Suction pressure = Static suction pressure - pipe pressure drop (suction side) - fitting pressure drop (suction side)
Differential pressure = Static discharge pressure + pipe pressure drop (discharge side) + fitting pressure drop (discharge side) - [Static suction pressure - pipe pressure drop (suction side) - fitting pressure drop (suction side)]
Differential pressure = Static discharge pressure - Static suction pressure + pipe pressure drop (suction and discharge sides) + fitting pressure drop (suction and discharge sides)
One of the parameters of pipe pressure drop and fitting pressure drop is the velocity. A lower volumetric flow rate of the fluid will have a lower velocity in which the diameter of the pipe remains unchanged (suction and discharge side). A lower velocity will causes lower pipe pressure drop andfitting pressure drop. Therefore, the head of a pump decreases also.
Differential head = Differential pressure / ρ g
Differential pressure = Discharge pressure - suction pressure
Discharge pressure = Static discharge pressure + pipe pressure drop (discharge side) + fitting pressure drop (discharge side)
Suction pressure = Static suction pressure - pipe pressure drop (suction side) - fitting pressure drop (suction side)
Differential pressure = Static discharge pressure + pipe pressure drop (discharge side) + fitting pressure drop (discharge side) - [Static suction pressure - pipe pressure drop (suction side) - fitting pressure drop (suction side)]
Differential pressure = Static discharge pressure - Static suction pressure + pipe pressure drop (suction and discharge sides) + fitting pressure drop (suction and discharge sides)
One of the parameters of pipe pressure drop and fitting pressure drop is the velocity. A lower volumetric flow rate of the fluid will have a lower velocity in which the diameter of the pipe remains unchanged (suction and discharge side). A lower velocity will causes lower pipe pressure drop andfitting pressure drop. Therefore, the head of a pump decreases also.
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