The
Effect of Pulsations on Cavitation in Reciprocating Pump Systems
J. C. Wachel/J. D. Tison/S. M. Price, ASME Paper 89-Pet-10,
1989.
Cavitation in reciprocating pump installations is a major cause
of piping and pump vibration and mechanical failures. Cavitation
occurs in pump systems when the negative peak of the dynamic pressure
wave, added to the steady state pressure, approaches the vapor pressure
of the liquid. Even in those systems which have ample net positive
suction head (NPSH) according to Hydraulic Institute Standards [1],
cavitation can occur. These standards specify that, in addition
to the net positive suction head required (NPSHR) by the manufacturer,
an allowance should be made for the inlet piping pressure drop and
acceleration head.
Acceleration
head calculations are an attempt to account for the dynamic behavior
of the system using quasi-static assumptions. In practice, these
calculations can be inadequate since they ignore the dynamic acoustical
response characteristics of the fluid.
Accurate calculations
of the pulsation levels inn pump systems must consider the dynamic
flow by taking into account all the parameters which significantly
influence the system, including the pump fluid end, the pump valves,
and the associated suction piping.
This paper
discusses the inadequacies of the acceleration head concept, and
describes how pulsation can contribute to cavitation. Simulation
of pump systems using a computer program to predict pulsation
and the onset of cavitation is discussed. Using these techniques,
cavitation and pulsation levels in the suction systems can be
predicted and the need for additional suction head properly evaluated.
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