SUN HYDRAULICS
QPAALCN

The accumulator sense, pump unload pilot valve is used to sense pressure in an accumulator at port 1 of the valve and when the pressure at port 1 reaches the valve setting, port 2 connects to port 3 to vent a relief valve and unload the pump. This valve has a 15% ratio between unload setting and reset; when pressure at port 1 falls below 85% of the valve setting, port 2 is blocked from port 3 and the pump will come back online to recharge the accumulator. This valve requires a separate check valve between port 1 and the pump. Another version of the accumulator sense, pump unload valve, QCDA, includes a free-flow check valve for pump flows under 12 gpm (50 L/min).

• The pressure differential between unload and reset will be within +/- 1% of the stated ratio of the valve with up to an additional 25 psi (1,7 bar) due to dynamic seal friction.
• The accumulator sensing area is positively sealed.
• The spool design of this 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.
• Minimum clearances between the spool and sleeve and a seal on the pilot piston diameter significantly reduce the potential for silting.
• When applying this cartridge, 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.
• Sun has designed a variety of standard accumulator/pump unload assemblies with a variety of features. These assemblies can be found on our website under SOLUTIONS: ACCUMLATOR SENSE, PUMP UNLOAD.
• Incorporates the Sun floating style construction to minimize the possibility of internal parts binding due to excessive installation torque and/or cavity/cartridge machining variations.

Additional Resources

• Sun Cartridges with EPDM Seals
• Sun Expands Corrosion-Resistant Solutions
• CavitySaver multi-function valves deliver single-cartridge solutions
• Series 4 PLUS Cartridges Offer Higher Flows with Lower Pressure Losses
• QuickDesign with SmartConnect Offers Drag-and-Drop Schematic Tool
• Accumulator Sense, Pump Unload Valves
• Sun Offers Zinc-Nickel Plating for Corrosion Resistance
• Manufacturing Sun Cartridge Cavities
• Circuit Savers
• Fluid and Temperature Recommendations
• Sun's Floating Style Screw-In Cartridge
• Performance Data
• Sun Model Code Explanation; 999-901-334
• Units of Measure, Settings, and Conversions
• Cartridges: Materials of Construction
• Cavity Information (S-171) and Tooling