Page 15 - Troubleshooting Paper Mill Hydraulics Sample Excerpt 2

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

To raise the cylinders, voltage is applied to the RRR-SV solenoid on
the pilot valve. Pilot pressure is directed internally to shift the main
spool into the “B” (crossed arrows) position. As the cylinders retract,
oil in the full piston sides return to the tank through the “A” and “T”
ports of the valve.

Each solenoid has a manual override on the end of the housing. Prior
to actuating the override, make sure all personnel are clear of the
machine. If an AC coil is used in the solenoid, the resistance of the
coil can be checked to verify if it is good. A reading below 50 ohms but
not zero normally means that the coil is good. If infinity is read, the
coil wires are open. If zero resistance is indicated then the coil wires
are shorted out to each other. This valve is a closed center, three
position, four way (with the “B” port plugged), double solenoid, spring
centered, spool valve.

23 Pilot Operated Check Valves

The check valves are used to lock oil in the rod sides of the cylinders.
The valves have no internal leakage therefore the cylinders will not
move once the no. 22 directional valve is de-energized. Oil will free
flow through the check valves when raising the rider roll. When
lowering the Rider Roll, oil is directed to the full piston sides of the
cylinder. At the same time, pressure will build up in the pilot lines of
the check valves in the opposite line. Approximately 1/3 of the
pressure is required to open the valves with the pilot line than is
locked in the cylinders. For example if 900 PSI is locked in one side of
the cylinders, then 300 PSI of pilot pressure will be required to open
the valves. Once the valves are open, the oil can exhaust out of the
cylinders and return back to the tank. Use extreme caution when
removing the lines between the check valves and cylinders, as
pressure will be maintained on the lines. If the cylinders drift when the
directional valve is de-energized then one check valve may be stuck
open or there may be trash in the pilot line. The cylinder’s piston seals
may also be bad.

Troubleshooting Papermill Hydraulics Page 45