An overcentre valve — also called a counterbalance valve — does two jobs at once. It holds a load against gravity when the control valve is centred, and it controls the descent when the operator lowers it, by metering the return oil so the load cannot run away.

The difference between an overcentre valve and a plain lock valve is the second job. A lock valve is open or shut. An overcentre valve opens progressively in proportion to pilot pressure, which is what gives smooth, controllable lowering of a boom or a raised platform.

A double overcentre valve does this in both directions — two elements in one body, each holding one side of the cylinder and each piloted open by the other. Use it wherever the load can act either way: a tilting deck, a crowd cylinder, a slewing motor, a winch that can be driven by its load.

Pilot ratio and setting

Set the overcentre pressure at least 30 per cent above the maximum load-induced pressure. Set it too close and the valve will chatter or lower jerkily; set it far too high and it will not open properly and the function will feel dead.

Also available: OVCDEL1202 10:1, the 1/2" valve with a 10:1 pilot ratio for loads that need a lower pilot pressure to release. Ask if you need it.

Manufactured by CBF Hydraulic, Montecchio Maggiore, Italy.