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.

These are sandwich plates that bolt between the subplate and the directional valve. The load holding is built into the valve stack, so there is nothing extra to plumb and no separate valve to mount out on the machine.

The trade-off against a cylinder-mounted valve: a modular overcentre cannot protect against a burst hose between the valve bank and the cylinder, because it sits on the wrong side of that hose. For a boom or anything overhead, mount the valve at the cylinder. For a machine where the hose run is short and protected, modular is neater.

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.

Bolt kits are not included. Order one sized for the finished stack height.

Manufactured by CBF Hydraulic, Montecchio Maggiore, Italy.