Installation
8
312877S
Tips to Reduce Cavitation
Cavitation in a diaphragm pump is the
formation and collapse of bubbles in the
pumped liquid. Frequent or excessive
cavitation can cause serious damage,
including pitting and early wear of fluid
chambers, balls, and seats. It may result in
reduced efficiency of the pump. Cavitation
damage and reduced efficiency both result in
increased operating costs.
Cavitation depends on the vapor pressure of
the pumped liquid, the system suction
pressure, and the velocity pressure. It can be
reduced by changing any of these factors.
1. Reduce vapor pressure: Decrease the
temperature of the pumped liquid.
2. Increase suction pressure:
a. Lower the installed position of the pump
relative to the liquid level in the supply.
b. Reduce the friction length of the suction
piping. Remember that fittings add fric-
tion length to the piping. Reduce the
number of fittings to reduce the friction
length.
c. Increase the size of the suction piping.
d. Increase the Net Positive Suction Head
(NPSH). See .
Performance Charts
,
page 23.
NOTE:
Be sure the inlet fluid pressure
does not exceed 25% of the outlet
working pressure.
3. Reduce liquid velocity: Slow the cyclic rate
of the pump.
Pumped liquid viscosity is also very important
but normally is controlled by factors that are
process dependent and cannot be changed to
reduce cavitation. Viscous liquids are more
difficult to pump and more prone to cavitation.
Graco recommends taking all of the above
factors into account in system design. To
maintain pump efficiency, supply only enough
power to the pump to achieve the required
flow.
Graco distributors can supply site specific
suggestions to improve pump performance
and reduce operating costs.
