The hydraulic balancing valve allows the unrestricted flow of oil from port 2 to port 1, as evidenced by the schematic diagram at the top of the figure below.
When the oil pressure in port 2 is greater than the pressure in port 1, the green part of the spool moves toward port 1 due to the force of the oil pressure, causing the check valve to open and allowing the oil flows freely from port 2 to port 1.
However, the flow of liquid from port 1 to port 2 is blocked until the pressure in the pilot port reaches a certain level, causing the blue spool to move to the left and opening the valve port. This allows oil to flow from port 1 to port 2.
If the pilot pressure is not strong enough to open the blue spool, the valve port closes and the flow of fluid from valve port 1 to valve port 2 stops.
The balancing valve symbol is shown below:
The role of the balance valve
Charge retention:
The balancing valve helps prevent unintentional downward movement of the hydraulic cylinder. This allows the operator to lift heavy objects at a specific speed and hold them in a fixed position.
Load Control:
The balancing valve prevents the actuator from moving before the hydraulic pump has a chance to respond. This helps eliminate actuator cavitation and reduces the risk of loss of load control.
Security charge:
In the event of a hydraulic system line bursting or seriously leaking, a balancing valve installed on the actuator helps prevent loss of control over the moving load.
Selection principles for balancing valve application and pilot ratio
The typical relief setting for balancing valves is generally 1.3 times the maximum operating pressure. However, the pressure required to activate a pilot valve depends on the pilot ratio.
Pilot pressure can be calculated using the following formula:
Pilot pressure = (relief pressure set point – charge pressure) / pilot ratio
To optimize load control and energy efficiency, the pilot ratio can be selected based on the following guidelines:
- A ratio of 5:1 is chosen when the load is highly unstable, as in the case of long jib cranes. This relationship is used when the load changes and has a significant impact on the mechanical structure.
- A 10:1 ratio is appropriate for applications where the load is relatively stable.
