Two pump high-low unloading assembly


Function for YRES
Port Designators [ + ]
Modifiers Ports
C, C/S All Ports: 1/2" NPTF;
D, D/S All Ports: 3/4" NPTF;
K, K/S All Ports: SAE 10;
L, L/S All Ports: SAE 12;
V, V/S All Ports: 1/2" BSPP;
W, W/S All Ports: 3/4" BSPP;
Technical Features [ + ]

This assembly allows the smooth unloading of a low-pressure / high-flow pump in a 2 pump high-low system. This type of system utilizes the flow of 2 pumps to provide rapid speed to an actuator. Once resistance is encountered, and the requirement switches from high speed to high force / torque, then the low-pressure / high-flow pump is unloaded back to tank at minimum pressure and all the available horsepower is directed to the high-pressure / low-flow pump. This assembly also provides a system relief valve.

  • The counterbalance valve in this assembly is not acting as a counterbalance valve; it is acting as a pressure sensitive unloading valve. The setting, however, relates to the counterbalance world. With the CB*A set at 4000 psi (280 bar), the circuit will start to unload with about 1000 psi (70 bar) of pressure and will fully unload somewhere above 1400 psi (90 bar).
  • Turn adjustment clockwise to decrease setting of the counterbalance valve.
  • Backpressure at port 2 of the counterbalance valve adds to the effective relief setting at a ratio of 1 plus the pilot ratio times the backpressure.
  • Counterbalance valve reseat exceeds 85% of set pressure when the valve is standard set. Settings lower than the standard set pressure may result in lower reseat percentages.
  • Back pressure on the tank port (port 2) of the relief valve is directly additive to the valve setting at a 1:1 ratio.
Technical Data [ + ]
Body Type Line mountLine mount
Capacity 30 gpm120 L/min.
Mounting Hole Diameter .34 in.8.6 mm
Mounting Hole Depth ThroughThrough
Mounting Hole Quantity 22
Performance Curves [ + ]
FAQs [ + ]

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

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.

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.
  • For detailed information regarding the cartridges contained in this assembly, click on the models codes shown in the Included Components tab.
Additional Resources [ + ]