Accumulator sense, pump unload assembly with air bleed


Function for XQCK
Port Designators [ + ]
Modifiers Ports
C, C/S Ports P, T, EF: 1/2" NPTF; ACC: 1/2" NPTF; Ports D & AUX: 3/8" NPTF; Gage Port: 1/4" NPTF;
K, K/S Ports P, T, EF: SAE 10; ACC: SAE 10; Ports D & AUX: SAE 6; Gage Port: SAE 4;
V, V/S Ports P, T, EF: 1/2" BSPP; ACC: 1/2" BSPP; Ports D & AUX: 3/8" BSPP; Gage Port: 1/4" BSPP;
Technical Features [ + ]

This valve assembly is meant to charge an accumulator using a fixed displacement pump. It incorporates a ventable priority flow control valve. When the pressure reaches the set point of the valve, the priority flow control is vented and all of the pump flow is available to the system. When the pressure drops to the value determined by the fixed percentage of the pilot valve, the priority flow is used to recharge the accumulator. Only the priority flow is directed to the accumulator leaving the rest of the pump flow available to the system.

The assembly has three additional features; a simple circuit that softens the unloading of the pump, a system over-pressure relief, and a valve that dumps the accumulator when the pump is powered down.

  • 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.
Technical Data [ + ]
Capacity 15 gpm60 L/min.
Body Type Line mountLine mount
Mounting Hole Thread .375-16 UNC - 2B in..375-16 UNC - 2B in.
Mounting Hole Depth .62 in.15,7 mm
Mounting Hole Quantity 22
FAQs [ + ]

Reasons to anodize:

  • To increase corrosion resistance. Sun uses 6061-T651 aluminum. It is one of the most corrosion resistant aluminum alloys there is. Whether or not anodizing improves the corrosion resistance of 6061 aluminum is debatable. We have yet to have a manifold returned because of corrosion.
  • Appearance (color). The 2 colors that would appeal to Sun would be blue or black. Unfortunately these are the colors that are hardest to do consistently.
  • To provide a hard wear surface. Sun does not make parts-in-body valves. The manifold is just plumbing. We don't need a wear surface.
  • Because everyone else does it. Bad reason. 

Reasons to not anodize:

  • Cost. It's another process.
  • Logistics. When you make tens of thousands of manifolds a month and you anodize hundreds, it's a problem. Consistency. See above.
  • Stamping. After a body is anodized you cannot do any more stamping without making a mess.
    Inspection. Have you ever tried to look for burrs in a black anodized body? It's the old blackboard factory at night scenario.
  • Torque. You will experience an increase in breakaway torque when removing items from an anodized manifold.
  • Fatigue life. This is the best reason to not anodize. Fatigue failure is a very complex phenomenon. What it takes to initiate a crack is difficult to predict. What it takes to propagate a crack is readily defined. Anodizing produces a very thin, very hard, and very brittle surface on aluminum. The first time you pressurize an anodized aluminum manifold you have initiated fatigue cracks. Whether or not the stress is enough to propagate the cracks is a matter of pressure and manifold geometry. Anodizing an aluminum manifold grossly reduces the fatigue life by anywhere from 20% to 50%.

Direct-acting valves are used to prevent over pressure, and pilot-operated valves are used to regulate pressure. If you are unsure, use a direct-acting valve. Sun's direct acting valves are very fast, dirt tolerant, stable, and robust. Sun's pilot-operated valves are moderately fast, they have a low pressure rise vs. flow curve, and they are easy to adjust.

There are exactly 250 Sun drops in a cubic inch or 15 in a cc.

Notes [ + ]
  • Important: Carefully consider the maximum system pressure. The pressure rating of the manifold is dependent on the manifold material, with the port type/size a secondary consideration. Manifolds constructed of aluminum are not rated for pressures higher than 3000 psi (210 bar), regardless of the port type/size specified.
Additional Resources [ + ]