Pump Troubleshooting Overview - Graco 8900 Instructions For Use Manual

Troubleshooting
Pump Troubleshooting
Overview
Pump Cavitation
Under normal operation, when the feed pump pressures
are balanced, component A and component B outlet
pressures are consistent.
Some up or down adjustments in feed pressures will be
necessary to keep the pumps' outlet pressures bal-
anced. This is due to viscosity differences in the two
materials, volumetric ratio, and required flow rate.
Because of the viscosity difference between the two
materials, most of the balancing effect comes from
adjusting the component A pressure. For ratios higher
than 1:1, the component B pressure should be set only
as high as necessary to avoid cavitation at the desired
flow rate. For 1:1 ratio there is equal balancing from
component A and component B pressure.
If either the A or B pump does not completely fill with
material on intake, the failing pump's material output is
interrupted at the beginning of the next stroke. This is
referred to as cavitation.
Pump A cavitation is detected by observing the inlet
pressure gauges on pump A and pump B immediately
after changeover. When cavitation occurs, the propor-
tioner pump outlet pressure gauge drops and the pump
A outlet pressure gauge shows an increase in pressure,
as described previously.
B pump cavitation is detected by observing the B pump
inlet pressure gauge immediately after pump top
changeover. When cavitation occurs, the B pump outlet
pressure gauge drops.
If the amount of cavitation is moderate, the pressure
gauges return to their normal readings at some point
during the downstroke of the failing pump.
During pump A cavitation, the pressure drop may cause
a noticeable reduction in flow rate at the dispense gun.
Additionally, the interruption in the pump A material out-
put may cause component B-rich material to dispense,
which may appear as poorly mixed material.
During B pump cavitation, the interruption in the B pump
material output may cause component A- rich material
to dispense, which may appear as poorly mixed mate-
rial.
38
Pump Failure to Seal
Under normal operation, the output of the component A
and component B pumps depends upon proper sealing
of their internal packings.
If packings fail to seal properly, the pump material out-
put, and thus the output pressure, is reduced. Depend-
ing on the location of the failure, the pressure reduction
may occur on the pump upstroke, downstroke, or both
strokes.
Component B Pressure Relief Valve
The proportioner includes a spring-loaded, overpressure
relief valve, which bypasses component B back to the
supply when pressures exceed 3400 psi (23 MPa, 234
bar).
309790ZAF