Balance Valve: The Structure and Working Principle

The hydraulic balancing valve allows the free flow of oil from port 2 to port 1, as we can see from the structural diagram at the top of the figure below.

structural diagram of hydraulic balancing valve

When the oil pressure at port 2 is greater than the pressure at port 1, the green part of the spool moves toward port 1 under the drive of the oil pressure, and the check valve opens and the oil can flow freely from port 2 to port 1.

The liquid flow from port 1 to port 2 is cut off until the pilot port pressure reaches a certain value to move the blue spool to the left, so that the valve port is open, the oil can flow from port 1 to port 2.

When the pilot pressure is insufficient to open the blue spool, the valve port closes.

Valve port 1 to valve port 2 fluid flow will be shut off.

The principle symbol of the balancing valve is as follows:

principle symbol of the balancing valve

The role of the balance valve

Load hold:

The balance valve prevents undesired downward movement of the hydraulic cylinder, the balance valve allows the operator to lift heavy objects at a certain speed and hold them in a certain position.

Load control:

The balancing valve prevents the actuator from acting before the hydraulic pump due to the energy of the actuator load, thus eliminating cavitation of the actuator and load loss.

Safety load:

When a line in the hydraulic line bursts or leaks badly, a balance valve mounted on the actuator prevents the loss of control of the moving load.

The role of the balance valve

Selection principles for balancing valve application and pilot ratio

The relief setting for balancing valves is generally 1.3 times the maximum working pressure, but the required pressure to open a pilot valve depends on the pilot ratio.

The pilot pressure can be calculated according to the following formula.

Pilot pressure = (relief pressure set point – load pressure)/pilot ratio

In order to optimize load control and energy utilization, the pilot ratio may be selected by reference to the following methods:

  • 5:1 Selected when the load is extremely unstable, e.g. long-arm cranes.
  • 5:1 is applied when the load changes and has an unstable effect on the mechanical structure.
  • 10:1 for applications where the load is relatively stable.

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