PMC MN-06001, Manual

Page: 35 / 66

PMCA-20
Manual
35
3. Cavitation
Cavitation occurs when the Metering Pump 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 cavitation are:
a. Material temperature is 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 245fa blown systems. 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 cavitation in the Transfer Pump. Ensure the drum is vented to
the atmosphere or a Desiccated Air Dryer Kit is installed as recommended by the
material supplier.
c. Air volume insufficient for Transfer Pump or Transfer Pump Air Valve partially closed
will limit the ability of the Transfer Pump to operate at its maximum capability.
d. Inlet Material Screen obstructed (See MAINTENANCE section).
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.
4. Pressure Loss: Discharge/Inlet Ball
Simultaneous observation of the material Pressure Gauge and Direction Indicator Light is
necessary to determine which direction the Metering Pump fails to maintain pressure. Refer
to the chart to determine problem:
Left Directional Indicator
Light ON Right 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 and Ball Seat Gasket.
For service see MAINTENANCE/Metering Pump Line .