Multiply the pump head by the pump's capacity, and then use a simple conversion number.
Flow = 300 gallons per minute of fresh water as measured coming from the pump discharge.
Head = 160 feet. We measured it at the discharge side of the pump and corrected it for the fact that the gage was two feet above the pump center line.
Note:If there were any positive head on the suction side of the pump that head would have to be subtracted. A negative suction head would be added to the discharge head.
The centrifugal pump pumps the difference between the suction and the discharge heads. There are three kinds of discharge head:
Static head. The height we are pumping to, or the height to the discharge piping outlet that is filling the tank from the top. Note: that if you are filling the tank from the bottom, the static head will be constantly changing.
Pressure head. If we are pumping to a pressurized vessel (like a boiler) we must convert the pressure units (psi. or Kg.) to head units (feet or meters).
System or dynamic head. Caused by friction in the pipes, fittings, and system components. We get this number by making the calculations from published charts
Suction head is measured the same way.
If the liquid level is above the pump center line, that level is a positive suction head. If the pump is lifting a liquid level from below its center line, it is a negative suction head.
If the pump is pumping liquid from a pressurized vessel, you must convert this pressure to a positive suction head. A vacuum in the tank would be converted to a negative suction head.
Friction in the pipes, fittings, and associated hardware is a negative suction head.
Negative suction heads are added to the pump discharge head, positive suctions heads are subtracted from the pump discharge head.
Here is the formula for measuring the horsepower out of the pump:
Flow = 300 gallons per minute of fresh water as measured coming from the pump discharge.
Head = 160 feet. We measured it at the discharge side of the pump and corrected it for the fact that the gage was two feet above the pump center line.
Note:If there were any positive head on the suction side of the pump that head would have to be subtracted. A negative suction head would be added to the discharge head.
The centrifugal pump pumps the difference between the suction and the discharge heads. There are three kinds of discharge head:Static head. The height we are pumping to, or the height to the discharge piping outlet that is filling the tank from the top. Note: that if you are filling the tank from the bottom, the static head will be constantly changing.
Pressure head. If we are pumping to a pressurized vessel (like a boiler) we must convert the pressure units (psi. or Kg.) to head units (feet or meters).
System or dynamic head. Caused by friction in the pipes, fittings, and system components. We get this number by making the calculations from published charts
Suction head is measured the same way.
If the liquid level is above the pump center line, that level is a positive suction head. If the pump is lifting a liquid level from below its center line, it is a negative suction head.
If the pump is pumping liquid from a pressurized vessel, you must convert this pressure to a positive suction head. A vacuum in the tank would be converted to a negative suction head.
Friction in the pipes, fittings, and associated hardware is a negative suction head.
Negative suction heads are added to the pump discharge head, positive suctions heads are subtracted from the pump discharge head.
Here is the formula for measuring the horsepower out of the pump:
Remember that we are using the actual horsepower or kilowatts going into the pump and not the horsepower or kilowatts required by the electric motor. Most motors run some where near 85% efficient.
An 85% efficient motor turning a 76% efficient pump, gives you a real efficiency of 0 .85 x 0.76 = 0.65 or 65% efficient.
A survey of popular pump brands demonstrates that pump efficiencies range from 15% to over 90%. The question then arises, "Is this very wide range due to poor selection, poor design, or some other variable which would interfere with good performance?" The best available evidence suggests that pump efficiency is directly related to " the specific speed number " with efficiencies dropping dramatically below a number of 1000 . Testing also shows that smaller capacity pumps exhibit lower efficiencies than higher capacity designs.
An 85% efficient motor turning a 76% efficient pump, gives you a real efficiency of 0 .85 x 0.76 = 0.65 or 65% efficient.
A survey of popular pump brands demonstrates that pump efficiencies range from 15% to over 90%. The question then arises, "Is this very wide range due to poor selection, poor design, or some other variable which would interfere with good performance?" The best available evidence suggests that pump efficiency is directly related to " the specific speed number " with efficiencies dropping dramatically below a number of 1000 . Testing also shows that smaller capacity pumps exhibit lower efficiencies than higher capacity designs.
Ref: mcnallyinstitute
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