Situations occur with any machine that lifts, lows or suspends a load that is outside of a machine designer’s control. Loss of pilot signal, directional valve returning to center, hose bursts, etc. should never result in an uncontrolled movement of a load or a platform. There are a couple of methods to design this safety circuit, and the first method considered for loads that can overrun is a counterbalance valve hydraulic arrangement.

How Load Holding Works

A load holding circuit or valve, generally a pilot operated check valve, keeps fluid trapped on the load side of the cylinder until a pilot pressure opens the check valve. The check valve seats, and the cylinder holds its position with very little leakage. This design is better suited for loads that are static or slowly moving. Loads held in this fashion could be a clamp, a stabilizer leg, or a slowly lifting load.

How Counterbalance Valves Differ

A counterbalance valve hydraulic serves many purposes. It is a check valve that also contains an adjustable relief element, creating back pressure on the return side of the cylinder. Counterbalance valves are also pilot operated, meaning that the valve opens only when a predetermined pilot pressure is built. The valve also modulates its opening based on the load. This helps create a smooth deceleration. Similar to other directional control valves, if the load tries to run beyond the capacity of the pump to fill the cylinder, the valve closes, to slow the cylinder down. This behavior creates a self-resetting or self-limiting valve, which is very desirable, especially on cranes.

Matching the Valve to the Load

The main difference when deciding between a check valve or counterbalance valve, is how the load behaves. A pilot-operated check valve is suitable when the load opposes movement, meaning that the pump provides all the energy for movement. If gravity can pull the load down faster than the pump can supply oil, the check valve cannot hold the load, and the valve will chatter or even drop the load suddenly. On the other hand, a counterbalance valve, can hold back pressure throughout the stroke.

Setting and Mounting Considerations

The relief setting for pressure reducing valves is usually set above the highest pressure a load can create. The valve is designed to stay closed until it is opened by a pilot. If the relief setting is set too low, the valve may allow load pressure to creep up. If it is set too high, load lowering can be jerky. Mounting the valve directly on the cylinder port or a short block protects the load if a hose should fail.

Safe Operating Maintenance

Valve trouble is often caused by contamination, and a tiny particle can leave a check valve or spool slightly open. This allows pressure to pass through and can cause the valve to stick. A slight drift is prevented by cleaning the valve regularly and checking the springs and seats. Adjustments should be made only with the load supported and pressure removed from the valve.

Working with a Reliable Supplier

Teutonic Engineering, based in Coimbatore, manufactures and supplies pressure control valves and manifolds for industry. It is convenient to source manifolds and valves from the same vendor, as they can be designed to match and suit each other.

Both types of valves have their place in safe circuit design, and which type is chosen depends on the requirements of the load. If the load only requires holding, the choice can be made based on the behaviors of the load and the pressure settings. Reviewing the mounting layouts can provide further insight to the designers of machinery regarding possible safety issues. This can result in fewer service calls being needed over the life of the machine.