36
4. Cavitation - Cavitation occurs when the Metering Pump (B, or C, page 10) 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 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 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 Desiccant Air Dryer Kit is installed as
recommended by the material supplier.
c. Air volume is insufficient for the Transfer Pump or if the Transfer Pump Air Valve
is partially closed, this will limit the ability of the Transfer Pump to operate at its
maximum capability.
d. Inlet Material Screen (O) 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.
5. Pressure Loss: Discharge/Inlet Ball - Simultaneous observation of the material
Pressure Gauge (H, K, page 10) and Directional Indicator Light (Y page 12) is necessary
to determine which direction the Metering Pump fails to maintain pressure. Refer to the
chart to determine the problem:
Left Directional Indicator
Light ON
Right Directional Indicator
Light ON
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, Ball Seat Gasket and the O-ring on the cage.
For service see MAINTENANCE/Metering Pump Line (Page 46).
To Next Page
Loading...
