Unloading Relief Valves

Parker’s robust and reliable unloading pressure control valves provide superior accumulator charge control by automatically charging up to the maximum setting and recharging once the minimum pressure setting is reached.  These valves are capable of handling flows up to 3.75 lpm (1 gpm) and pressures as high as 420 bar (6000 psi). Internally or externally piloted options are available and are ideal for unloading pump pressure and maintaining accumulator pressure for several energy recovery or saving applications such as dynamic or parking brake circuits on mobile or industrial machinery.

Markets:
• Agriculture
• Construction
• Material Handling
• Miscellaneous Industrial
• Miscellaneous Manufacturing
• Miscellaneous Mobile

Features/Benefits:
• Low hysteresis
• Hardened working parts for maximum durability
• All external parts zinc plated

Applications:
• Accumulator circuits

Additional Technical Insight:
Parker’s RU101, RU104, and M04A4J offer design flexibility by allowing the use of hydraulic components to automatically control pump flow to one or more accumulators.  These are low flow pilot valves that can be used to control higher pump flows in fixed displacement or load sense systems.

The RU101 is externally piloted and rated for flows up to 1 GPM and pressures up to 3000 psi.  It is typically used with fixed displacement pumps and can directly unload flows up to 1 GPM or be used to pilot a logic element to unload higher pump flows.  Once the accumulators are charged to the adjustable or factory preset maximum pressure, the pump will automatically unload back to tank.  Due to the differential area design, when the pressure drops to 80% of the RU101 maximum setting, the unloading valve will direct pump flow to the accumulators for recharging.

The RU104 is externally piloted and designed to control signal pressures up to 3600 psi. It is typically used with load sense or fixed displacement pumps to control accumulator pressures. The valve responds to accumulator pressure and will connect the sense port to pressure or tank accordingly. When the accumulators are fully charged (high) the RU104 will unload and vent the sense port to tank causing a load sense pump to de-stroke and go to stand-by pressure. When accumulator pressure drops to approximately 80% of the unload pressure the RU104 will reload, connecting the sense port to pressure, raising pressures until the accumulators are fully charged causing the RU104 to repeat the unloading cycle again.

The M04A4J is internally piloted and is rated for flows up to .53 GPM and pressures as high as 6000 psi.  It is typically used with load sense pumps to control accumulator charging.  When the accumulators are charged to the unload pressure, the pump’s load sense port is directed to tank allowing the pump to go to its standby pressure.  Once the accumulator pressure falls to the M04A4J reload pressure, the pump’s load sense port is fed the accumulator pressure and the pump comes on stroke to charge the accumulator back up to the unload pressure.  Controlling only the pump load sense signal allows a small cartridge valve to control a wide range of flows from small to larger displacement load sense pumps.

Parker’s unloading pressure control valves offer design flexibility by allowing in-line mounting with standard line bodies, or integration into more complex custom manifolds.  They can also be combined with K04G3 shuttles for use in critical applications that require redundant accumulators such as braking and steering.  By hydraulically controlling pump unloading for accumulator charging, there may be no need for solenoid valves, pressure sensors, electronic controls, and the associated wiring.  Combining the features of the RU101, RU104, or M04A4J with the many other products offered by Parker’s Hydraulic Cartridge Division allows for application specific solutions for some of the most demanding applications, including: Construction, Mining, Industrial Power Units, Oil and Gas, Marine, Material Handling.