POLYURETHANE
MACHINERY
CORPORATION
PH-2 SERVICE MANUAL
12. TROUBLESHOOTING
• Problem: Cavitation.
Solutions:
1. Cavitations occur when the Metering Pump (B or C, section 5) 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 Trans-
fer 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 maxi-
mum capability.
d. Inlet Material Screen (M, section 5) obstructed (See MAINTENANCE sec-
tion, 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.
• Problem: Pressure Loss: Discharge/Inlet Ball.
Solutions:
1. Simultaneous observation of the material Pressure Gauge (E, F, section 5) and
Direction Indicator Light (Q, section 5) is necessary to determine which direction
the Metering Pump fails to maintain pressure. Refer to the chart to determine
problem:
Left Arrow Directional
Indicator Light ON
Right Arrow 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. For service see MAINTENANCE: METERING PUMP-LINE (page 50).
REVISION 1.2 41
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