Page 3 - Troubleshooting Paper Mill Hydraulics Sample Excerpt 2

No. 3 P.M. Winder Power Supply and Rider Roll

1A Pump

This 46.7 GPM, variable displacement, externally drained, pressure
compensating piston pump supplies a volume of oil to the no. 3 P.M.
Winder circuits. The pump will deliver maximum flow whenever
pressure in the system is below the setting of the compensator. When
the pressure reaches the compensator setting, the pump will
de-stroke to deliver only the amount of oil necessary to maintain the
compensator setting in the line.

The compensator should be adjusted to 200 PSI above the pressure
required to do the heaviest amount of work. Please refer to our Basic
Hydraulic Troubleshooting manual, Hydraulics Pump section, for the
procedure for setting the pump compensator. If the compensator is
set too low, the machine will stall under heavy loads. A setting that is
too high will result in shock and perhaps damage to the machine. The
compensator valve can fail either open or closed.

If the valve fails open, the pump will be de-stroked to a near 0 GPM
flow rate and the pressure at the outlet port will be very low. If the
valve fails closed, the pump will never compensate and will deliver
maximum flow at all times. With no relief valve in this system,
pressure will continue to build until a weak point in the system
ruptures or the electric motor kicks out. If either problem exists, turn
the pump off and make sure the pressure at the outlet port is 0 PSI.
Remove the compensator from the pump and take it apart. Inspect
the hollow orifices in the valve spool for contamination. Make sure
that there is no trash inside the compensator housing, Verify that the
spring is not bent, broken or rusted. Re-assemble the compensator
and attempt to reset the spring to the proper setting.

Oil that bypasses internally across the tight tolerances in the pump
will drain back to tank through the case drain to keep pressure from
building against the shaft seal. As the pump wears, these tolerances

Troubleshooting Papermill Hydraulics Page 33