Hydraulic problems and their resolutions, actual examples

Jul 13, 2021

The following is a sampling of real life examples of hydraulic problems Valmet Field Service experts found in the field and rectified during their visit. Regardless of the area - wet end, press section, dry end, finishing - they represent the types of issues we run into on a regular basis when performing services onsite, including audits or process and condition tests. If there are problems, we'll work with your craftspeople to take care of them.


Problem: Press end loading pressure was oscillating 400 psi every 2.5 minutes.

Fix: Found and fixed problem with 2 power supplies talking to each other.


Problem: Winder lowering cylinders and counterbalance valves failing every 3 months.

Fix: Added new pilot line to both counterbalance valves.


Problem: Oil hot.

Fix: Found heat exchanger plugged with sediment. Backflushed and OK.


Problem: After installation of spare Sym ZS roll, concerns about how to restart.

Fix: Let oil run for 1 hour before turning, then 1.5 hour in crawl before running. Start-up OK.


Problem: Felt stretcher proportional valve not working.

Fix: Inlet flow control valve closed too much. Opened valve and used downstream flow control valve to set stretcher speed. Recalibrated proportional valve with higher supply pressure.


Problem: After installation of a controlled crown roll, oil leaked out the seal.

Fix: Found that the scavenger pump was changed and pump cartridge was installed backwards and was pumping oil into the roll. Reinstalled cartridge correctly, cleaned oil out and OK.


Problem: Oil temperature was high at 160 degrees.

Fix: Main pressure relief valve dumping oil. Changed same.


Problem: SymZS roll Moog valves measurement changing.

Fix: Suspect bad pressure transmitter on board. Changed valve out.


Problem: Unstable and low pressures in hydraulic circuits.

Fix: Main cartridge relief valve loose in cast iron housing. Fixed.


Problem: Heavy vibrations in calender SymZ roll hydraulic circuits.

Fix: Moog valve internal oil filter screens plugged. Fixed.


Problem: New reel secondary arm cylinder kicking roll out too slow.

Fix: Air was in cylinder, didn't bleed air after installation. Bled air and OK.


Problem: Vibration in hydraulic lines.

Fix: Wire to proportional valve was loose, checked all wiring terminations, tightened as needed.


Problem: Press hydraulic pressure oscillating.

Fix: Pump pressure compensators not set up correctly. Fixed.


Problem: Not able to run at low nip loads in press.

Fix: Differential pressure transmitter calibration wrong. Recalibrated and OK.


Problem: Rider roll on winder would not raise up.

Fix: Found Moog valve shorted out, replaced it.


Problem: Press loading not responding.

Fix: Found potentiometers out of calibration range for computer to act upon. Recalibrated pots.


Problem: Pressure spikes on calender.

Fix: Possible air in proportional valves. Bled air out and OK.


Problem: SymBelt would stop when it goes to "Load".

Fix: Bad pilot solenoid valve that dumps zone pressures. Replaced and OK.


Problem: SymSizer loading erratically.

Fix: Rolls were scissored. Fixed.


Problem: OptiLoad stack would not load up on one end.

Fix: Hand valve to stack was shut off when calibrating a transmitter. Fixed.


Problem: Not getting a flat nip load on 2nd press (straight through).

Fix: Found TS cylinder leaking past seals by removing load side cylinder port, capped off load supply tube, loaded press, compared field pressure reading to bench gauge to be the same.


Problem: Oil temperature was high going to press section.

Fix: Cooling water filter plugged. Changed it and OK.


Problem: Supercalender not closing evenly, DS faster than TS.

Fix: Changed TS valve and card, no luck. Found terminations to DS valve loose. Tightened and OK.


Problem: Losing system pressure.

Fix: Found unloading proportional valve dumping to tank. Changed it out and OK.


Problem: Primary arms not stopping smoothly, i.e. jerky movement.

Fix: Flow control pilot valve for primary turning cylinders came loose. Reset flow valve and OK.


Problem: SymSizer nip load uneven and opens on one side after nipping up.

Fix: Recalibrated pressure transmitters, put in roll change position, then bled air out hydraulic lines.

For more information on hydraulic maintenance and troubleshooting, refer to existing Up & Running articles and contact your Valmet representative.