PMC PH-2 - Cavitation and Pressure Loss Issues

PH/PHX-2 Manual
40
5. Cavitations
Cavitations occur when the Metering Pump (B or C, page 14) requires a larger volume of
material than the supply system (Transfer Pump) can furnish. This creates a "void" of
material in the Metering Pump. The most common causes of cavitations are:
a) Material temperature too low causing increased material viscosity resulting in the
inability of the Transfer Pump to maintain sufficient supply to the Metering Pump.
This is most common with today's blowing agents. Ensure the material
temperature in the drums is no lower than the material suppliers' recommendation.
b) Failure to vent the material drum while drawing material out with the Transfer Pump
causes a vacuum and cavitations in the Transfer Pump. Ensure the drum is vented
to the atmosphere or a Desiccated Air Dyer Kit is installed as recommended by the
material supplier.
c) Insufficient air volume for Transfer Pump or a partially closed Transfer Pump Air
Valve will limit the ability of the Transfer Pump to operate at its maximum
capability.
d) Inlet Material Screen (M, page 14) obstructed (See MAINTENANCE section,
page 46).
e) Metering Pump Inlet Ball does not seat properly allowing material to flow back into
the Material Delivery Hose when the Metering Pump is on the "Discharge" stroke.
This causes the volume of material on that Metering Pump to be less on the
discharge stroke resulting in intermittent off-ratio material and Pressure Gauge
fluctuation.
6. Pressure Loss: Discharge/Inlet Ball
Simultaneous observation of the material Pressure Gauge (E, F, page 14) and
Direction Indicator Light (Q, page 15) is necessary to determine which direction the
Metering Pump fails to maintain pressure. Refer to the chart to determine problem:
Directional
Indicator Light ON
Directional
Indicator Light ON
Iso Pressure Gauge
FALLS
Iso Inlet Ball does not seat
properly
Iso Discharge Ball does not
seat properly
Poly Pressure Gauge
FALLS
Poly Discharge Ball does
not seat properly
Poly Inlet Ball does not
seat properly
In most cases the cause of a leaking Inlet/Discharge Ball is foreign material preventing
the Ball from seating properly. If the above steps do not resolve the problem, replace
the appropriate Ball, Ball Seat.
For service see MAINTENANCE/Metering Pump Line, page 48.
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