Counterbalance valves are also known as load control, over-centre, motor overrun valves or hose burst valves.
Their most common use is for supporting loads in lifting applications such as cranes, scissor lifts or excavators. They ensure the load does not drop when the power is turned off. They also control the load lowering to make sure it is safe and stable.
When machine loads change direction or go over-centre then counterbalance valves compensate for the effect of load pressure change on flow through the restricting orifice, this helps to control the load and therefore allows the system to work at a more consistent speed.
A simple way to think of a load control valve is as a pilot operated relief valves mounted on the cylinder port. With no pilot pressure, the cylinder will only move when the pressure exceeds the relief valve setting. When pilot pressure is applied, the pressure at which the main unloading relief valve opens is lowered to one that allows safe load lowering control. But the clever part is that if the load tries to ‘run away', faster than the supply flow requires, the diminishing pressure is fed back via the pilot lines to close the main control section and further restrict the load movement. This is the internal closed loop operation of the valve that makes them difficult to set up and suffer from instabilities under some operating conditions.
The term ‘pilot pressure ratio' is used to describe the internal area ratio of the valve. Different area ratio valves are used to open the valves at different pilot pressures and provide more stability or efficient operation in different machine designs. Understanding how the pilot signal is generated and exactly what and where the drain signal comes from is key to understanding how they will work.
A check valve is used to allow fluid to flow back through the counterbalance valve without restriction. This allows the load to be raised with minimal pressure loss through the valve.
The vast majority of counterbalance valves are used as cylinder load control systems or motor overrun or hose break protection. They are ideally mounted directly onto the actuators and therefore tend to be cartridge designs for insertion into the actuator mounted manifolds.
The valves themselves come in a wide range of different options and versions. Direct acting or differential area, different pilot ratios, more restrictive versions, single or two and available with many pilot line and drain line or vent connections. There are significant differences between the design detail from different manufacturers and because of their complex operation, there can be significant performance variations between these manufacturers.
Learn more about counterbalance valves in our 'Professional Training Section'. Understand their design features, performance limits, and how to specify counterbalance valves.