Page 124 - Fluid Power Engineering

98 Cha pte r F o u r

1 Boiling point at atmospheric pressure T max Maximum operating temperature
2 Boiling point at T max P min Minimum allowable operating pressure
FIGURE 4.8 Determination of the minimum allowable operating pressure.

This undesirable phenomenon can be avoided by taking the follow-
ing actions, whenever possible:

• Reduce the pressure losses in the pump inlet line by increasing
the suction line diameter and decreasing its length.
• Avoid using the inlet line filter and other local-loss elements.
• Increase the pump suction pressure by doing one of the
following:
• Use a booster pump.
• Use a closed pressurized tank.
• Mount the pump below the tank by a convenient distance.

4.5 Pulsation of Flow of Displacement Pumps
Theoretically, the pump flow rate is calculated as Q = V n. This
g
expression gives the average or mean pump flow rate. Actually,
the pump flow rate is not constant. Each pumping chamber delivers
a flow rate that equals the rate of reduction of its volume. The net
pump flow rate at a certain instant is the summation of the flow
rates delivered by the chambers connected to the delivery port at that
instant.
The flow rate delivered by the pumping chamber starts at a
zero value at the beginning of the delivery stroke. It increases pro-
gressively until it reaches its maximum value at the midpoint of the