How It Works
What is a Counterbalance Valve?
A counterbalance valve (also called a load-holding valve or overcenter valve) is used to control overrunning loads in hydraulic systems. It prevents uncontrolled movement when the load tries to drive the actuator faster than the pump can supply oil.
Common applications include:
- Crane boom cylinders (lowering heavy loads)
- Forklift mast cylinders
- Winch motors (lowering loads)
- Press cylinders (return stroke with spring force)
- Vertical axis actuators
How Counterbalance Valves Work
A counterbalance valve combines two functions:
- Relief function: Blocks return flow until load-induced pressure exceeds the valve setting
- Pilot-operated check: Opens based on pilot pressure from the opposite work port
When lowering a load, pilot pressure from the pump opens the counterbalance valve in a controlled manner, allowing the load to descend at the speed set by the pump flow, not by gravity.
Pilot Ratio
The pilot ratio is the ratio of relief pressure to pilot pressure needed to fully open the valve:
Pilot Ratio = Relief Setting / Required Pilot Pressure
For example, a 3:1 ratio valve set at 300 bar requires 100 bar pilot pressure to fully open.
- Low ratio (1.3:1 to 2:1): Requires high pilot pressure, very smooth control, used for precision applications
- Medium ratio (3:1 to 4:1): Balanced control and efficiency, most common
- High ratio (4.5:1 to 10:1): Opens with low pilot pressure, less smooth, efficient for light loads
Selecting the Correct Pilot Ratio
The minimum pilot ratio should ensure the valve opens reliably under all load conditions. The calculation is:
Minimum Pilot Ratio = (Load-Induced Pressure x Safety Factor) / System Pressure
Where:
- Load-Induced Pressure: Pressure generated on the rod side by the overrunning load
- Safety Factor: Typically 1.3 to allow for setting tolerance and pressure variations
- System Pressure: Available pilot pressure when lowering
Check Valve Setting
Most counterbalance valves include an integral check valve to allow free flow in the lifting direction. The check valve cracking pressure is typically:
- Standard: 3-5 bar (45-75 psi)
- Low pressure: 0.5-2 bar (7-30 psi)
Counterbalance Valve Sizing
Calculate recommended pilot ratio and check valve settings for counterbalance valves controlling overrunning loads.
Recommended Pilot Ratio Range
Results
Pilot Ratio Selection Guide
| Ratio | Application | Characteristics |
|---|---|---|
| 1.3:1 | Precision positioning | Smoothest, high back pressure |
| 2:1 | Cranes, aerial lifts | Very smooth, good efficiency |
| 3:1 | General industrial | Standard, balanced |
| 4.5:1 | Mobile equipment | Good efficiency, adequate control |
| 8:1 - 10:1 | Light loads, fast cycle | Efficient, less smooth |
Standard Available Ratios
| Manufacturer | Common Ratios |
|---|---|
| Sun Hydraulics | 1.3:1, 3:1, 4.5:1, 8:1 |
| Parker | 1.5:1, 3:1, 5:1, 10:1 |
| Eaton Vickers | 2:1, 3:1, 4.5:1 |
| Bosch Rexroth | 1.5:1, 3:1, 4.5:1, 8:1 |
Installation Guidelines
| Guideline | Recommendation |
|---|---|
| Valve location | As close to cylinder as possible |
| Relief setting | 1.3x load-induced pressure minimum |
| Flow rating | Match or exceed max cylinder flow |
| External drain | Required for most cartridge valves |