(hp constant

(m constant)

For centrifugal pumps, the following equations hold:

fhp _ f fff 550gc npP

QfPghp55Ggc _ —hp bhp bhp system efficiency ns = np x nm (motor efficiency)

It is important to select the motor and pump so that at nominal operating conditions, the pump and motor operate at near their maximum efficiency.

For systems where two or more pumps are present, the following rules are helpful. To analyze pumps in parallel, add capacities at the same head. For pumps in series, simply add heads at the same capacity.

There is one notable difference between blowers and pump performance. This is shown in Figure I.20. Note that the bhp continues to increase as permissible head goes to zero, in contrast to the pump curve when bhp approaches zero. This is because the kinetic energy imparted to the fluid at high flow rates is quite significant for blowers.

Manufactures of fluid-handling equipment provide excellent performance data for all types of equipment. Anyone considering replacement or a new installation should take full advantage of these data.

Fluid-handling equipment that operates on a principle other than centrifugal does not follow the centrifugal scaling laws. Evans8 gives a thorough treatment of most types of equipment that would be encountered in industrial application.

18 in. diameter 3450 rpm

18 in. diameter 3450 rpm

1500 2000

Flow rate (cfm)

0 0

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