Pumps Design Rules of the Thumb - Engineersfield

Pumps Design Rules of the Thumb

Pumps Design Rules of the Thumb

Power for pumping liquids; HP=(gpm)(psi difference)/(1714)(fractional efficiency).

Normal pump suction head (NPSH) of a pump must be in excess of a certain number, depending on the kind of pumps and the conditions, if damage is to be avoided.

NPSH= (pressure at the eye of the impeller – vapour pressure)/(density). Common range is 4 ― 20 ft.

Specific speed Ns= (rpm)0.5 (gpm)/ (head in ft)^0.75. Pump may be damaged if certain limits of Ns are exceeded and efficiency is best in some ranges.

Centrifugal pumps: single stage for 15-5000 gpm, 500 ft max head; multistage for 20―11,000gpm, 5500 ft max head. Efficiency 45% at 100 gpm, 70% at 500 gpm, 80% at 100,000gpm.

Axial pumps for 20―100,000 gpm, 40 ft head, 65-85% efficiency.

Rotary pumps for 1―5000gpm, 50,0000 ft head, 50―80-% efficiency.

Reciprocating pumps for 10-10,000pgm, 1,000,000 ft head max. Efficiency 70% at 10HP, 85% at 50 HP, 90% at 500 HP.

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