By Bob Wojcik
Stand-alone relief valves are relatively simple to set properly. After installing a relief valve in a circuit, with the pressure port connected to the pressure line and the tank port connected directly to the reservoir, adjust the relief valve to its lowest possible pressure setting. This will avoid an unexpected condition when the hydraulic power is applied to the circuit with this newly-installed relief valve.
Once the relief is properly installed and set at its minimum setting, turn on the fluid power. There may be noise coming from the relief valve, as flow may be racing through the relief when it is at its lowest pressure setting. Next, begin to increase the relief valve setting and monitor the pressure gauge associated with the circuit of this new relief valve. This method for setting a system relief valve is common to a circuit with a fixed displacement pump.
When the system includes a relief valve used in a pressure compensated pump circuit, this setting procedure becomes a little more complicated!
As described above, install the relief valve in the circuit with the pressure port connected to the pressure line and the tank port connected directly to the reservoir. Ensure that the relief valve is adjusted to its lowest possible pressure setting. Again, this avoids an unexpected condition when the hydraulic power is applied to the circuit with this newly-installed relief. Once properly installed, set both the pump compensator and the newly-installed relief valve to their minimum settings. Start the hydraulic pump and begin to turn the system relief valve to nearly the maximum adjustment position. Now begin to adjust the pump pressure compensator to a setting about 200 PSI above the final desired system pressure setting. Next, begin to reduce the setting on the system relief valve until the pressure on the pressure gauge begins to drop below the pressure setting of the pump compensator. Now, lock the system relief valve at the position that remains the 200 PSI above required pressure. Last, set the pump pressure compensator setting to the actual system pressure that is required.
Remember, the system pressure relief valve must be set about 200 PSI above the pump pressure compensator setting, or the two pressure settings will fight each other. This would result in the system acting as if it were a fixed displacement system. Loud noises can be generated by the pump and this condition will also begin to develop high heat generation in the hydraulic fluid!
Quality Hydraulics & Pneumatics, Inc. offers design, products, and systems for the improvement of machine performance, in both mobile or industrial circuits, and their hydraulic systems. The Certified Fluid Power Specialists at Quality Hydraulics will assist in selecting the most appropriate components and systems to provide the most efficient and cost effective solutions.