Accumulator sense, pump unload assembly

• D, D/S

  Ports P, T, & SYS 1: 3/4" NPTF; Port SYS 2: 1/2" NPTF; Port G: 1/4" NPTF; Ports D & AUX: 3/8" NPTF;
• E, E/S

  Ports P, T, & SYS 1: 1" NPTF; Port SYS 2: 3/4" NPTF; Port G: 1/4" NPTF; Ports D & AUX: 3/8" NPTF;
• L, L/S

  Ports P, T, & SYS 1: SAE 12; Port SYS 2: SAE 10; Port G: SAE 4; Ports D & AUX: SAE 6;
• M, M/S

  Ports P, T, & SYS 1: SAE 16; Port SYS 2: SAE 12; Port G: SAE 4; Ports D & AUX: SAE 6;
• W, W/S

  Ports P, T, & SYS 1: 3/4" BSPP; Port SYS 2: 1/2" BSPP; Port G: 1/4" BSPP; Ports D & AUX: 3/8" BSPP;
• X, X/S

  Ports P, T, & SYS 1: 1" BSPP; Port SYS 2: 3/4" BSPP; Port G: 1/4" BSPP; Ports D & AUX: 3/8" BSPP;

This valve assembly is meant to charge an accumulator using a fixed displacement pump. When the pressure reaches the set point of the valve, the pump is unloaded. When the pressure drops to the value determined by the fixed percentage of the pilot valve, the pump is brought back on line to recharge the accumulator. The ventable relief serves a dual purpose as a main stage to unload the pump and as a system over-pressure relief. The assembly has an additional feature; a simple circuit that softens the unloading of the pump.

• When applying this assembly, a separate drain line is required to prevent erratic operation caused by tank line pressure fluctuations.
• NOTE: Careful consideration should be given when selecting an adjustment range. System pressure drops and flows tend to affect the operation of unloading valves. Low operating pressures combined with low differentials result in a very narrow band between unload and reset, requiring precise system design. High flow rates typically mean high pressure drops, which subtract from the differential the valve has to work with.
• The pressure setting and the resultant reseat pressure are in reference to the port 2 area of the QCD* pilot valve. Pump pressure will be higher and accumulator pressure will be lower due to pressure drop caused by flow.
• The porting on this assembly is large in relation to its capacity. This is done to encourage the use of correspondingly large piping to minimize problems caused by flow induced pressure drop.
• The spool design of the pilot valve allows it to maintain a fixed differential ratio because the areas are created by diameters on the spool that will not wear or change with use.
• The accumulator pilot valve must be set below any reliefs in the pump side of the system or severe heating could occur.
• The relief in this package is meant to be an over-pressure device. It is set higher than the highest setting of the pilot valve and capped.

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