What Is a Counterbalance Valve?
Counterbalance valves are widely used in hydraulic systems where a load has the potential to move an actuator faster than the hydraulic supply can control it.
A common example is a vertically loaded hydraulic cylinder. If gravity acts in the same direction as the cylinder movement, the weight of the load can effectively drive the cylinder. This is known as an overrunning load.
Without suitable load control, the actuator may accelerate uncontrollably, potentially causing unstable movement and creating low pressure or cavitation on the inlet side of the actuator.
A counterbalance valve provides a controlled resistance to the oil leaving the actuator.
How Does a Counterbalance Valve Work?
A counterbalance valve is normally installed in the line between the load-supporting side of the actuator and the directional control valve.
When the actuator is stationary, the counterbalance valve prevents flow from leaving the actuator and therefore helps to hold the load in position.
When controlled movement is required, pressure from the opposite side of the actuator is applied to the valve’s pilot port.
This pilot pressure acts against the valve setting and allows the counterbalance valve to progressively open.
The load can then move while the valve maintains sufficient resistance to prevent it from running ahead of the hydraulic supply.
In simple terms, the valve allows the hydraulic system to remain in control of the load rather than allowing the load to control the actuator.
Why Is Back Pressure Required?
An important principle to understand is that the counterbalance valve deliberately creates resistance to flow.
As oil attempts to leave the loaded side of the actuator, the valve restricts that flow and maintains pressure upstream of the valve.
This pressure provides the hydraulic resistance required to control the overrunning load.
This illustrates an important principle in hydraulic engineering:
Pressure is created by resistance to flow.
The pump supplies flow, while resistance within the system determines the pressure required to move that flow.
Pilot Assistance
Counterbalance valves normally include a pilot connection from the opposite actuator line.
Pilot pressure assists in opening the valve when movement is commanded.
The relationship between pilot pressure and the pressure acting at the load port is determined by the valve’s pilot ratio.
For example, a valve with a 3:1 pilot ratio requires considerably less pilot pressure to assist opening than would be required if the valve relied solely on pressure at the load port.
Pilot ratio therefore influences both load stability and the pressure required to move the actuator.
Selecting an appropriate pilot ratio is an important part of counterbalance valve application.
Valve Setting
The counterbalance valve must be set sufficiently high to prevent the maximum expected load from opening the valve by itself.
In practice, the setting is normally selected above the pressure generated by the load, providing a suitable margin to ensure that the load remains controlled.
However, simply increasing the setting is not necessarily beneficial.
An unnecessarily high setting increases the pressure required to move the actuator and can increase energy losses and heat generation.
As with many hydraulic components, correct selection involves balancing stability, safety and efficiency.
Why Not Use a Simple Relief Valve?
Although a counterbalance valve has similarities to a relief valve, its function is different.
A relief valve primarily protects a hydraulic system from excessive pressure.
A counterbalance valve is specifically designed for load control.
It typically combines a pressure-control element, pilot assistance and a check valve that allows relatively unrestricted flow in the opposite direction.
This allows free flow into the actuator while controlling flow leaving the actuator when an overrunning load is present.
Typical Applications
Counterbalance valves are commonly found on:
- Hydraulic lifting equipment
- Mobile machinery booms
- Cranes and access platforms
- Hydraulic presses
- Tilting mechanisms
- Vertical cylinders
- Hydraulic motors driving overrunning loads
Wherever gravity or an external force can drive an actuator, some form of load-control strategy should be considered.
Engineering Insight
A counterbalance valve should not simply be regarded as a valve that “holds a cylinder up.”
Its more important function is to maintain control of the energy contained within a moving or suspended load.
Understanding the interaction between load-induced pressure, pilot pressure, valve setting and pilot ratio is therefore essential when designing or analysing load-holding hydraulic circuits.
Watch the accompanying Hydraulics Academy video for a visual introduction to how a counterbalance valve controls an overrunning load.
Hydraulics Academy — practical hydraulic engineering explained clearly.