Many hydraulic systems on the paper machine use pressure compensated pumps. This type of pump is normally an axial piston type with a variable swashplate which limits the piston strokes. The pressure compensator adjuster (as shown in the figure) uses a bias spring that adjusts the swashplate angle which controls oil flow from the pump.
Recall that pumps don’t generate pressure, they generate flow and resistance to flow generates the pressure. When there is no need for oil flow, the swashplate reduces the piston's stroke.
Included in the circuit with this type of pump is a pressure relief valve which will dump oil if the pressure gets too high. This valve is normally set about 150 psi above the system’s normal working pressure.
Setting up a new pressure compensated pump is fairly straight forward. Check the manufacturer’s operating manual for setting up new hydraulic pumps. For new pump installations, remember to fill the pump with filtered oil before starting the pump. Don’t just depend on gravity to fill the pump. Also, there will always be a small flow of oil from the case drain back to the tank. This is normal.
For more information on pumps and paper machine maintenance and services, contact your Valmet representative.