Why must the load holding valve be mounted directly on the cylinder port?
If a hose sits between the load holding (counterbalance) valve and the cylinder, that hose forms an unprotected zone: if the hose bursts, the valve cannot hold the load and the load falls freely. This is why the valve is mounted directly on the cylinder port, as close to the actuator as possible. Standards such as ISO 4413 and EN 13000 also require this arrangement.
The job of the load holding valve is to prevent the load from creeping down under its own weight. The load descends in a controlled manner only when pilot pressure reaches the valve, that is, when the operator deliberately gives a lowering command.
The zone where this protection applies is the volume between the valve and the cylinder. Every hose, fitting and pipe in between falls outside that protection:
- If the valve is bolted to the cylinder port (flanged or via a port block), there is no hose to burst; even if the line is severed the valve closes and the load stays in place.
- If the valve is separated from the cylinder by a hose, a burst of that hose drops the load suddenly. The valve is intact, but there is no oil left on the side it protects.
The same logic applies to distance: the shorter the distance between valve and cylinder, the lower the risk. In some applications the valve is embedded in a block welded directly onto the cylinder.
An important detail: the load holding valve setting pressure is generally chosen at 1.3-1.5 times the highest pressure generated by the load. Too low a setting causes the load to creep, too high a setting causes a harsh, juddering descent.
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