How much less pilot pressure is needed to open the valve than the pressure it is holding back. A higher ratio means the valve opens with less pilot pressure. It is the defining specification of an overcentre valve and the main decision when selecting one.

Because a high ratio makes the valve respond to small pilot changes with large movements, so any compliance in the circuit - long hoses, flexible mounts, a swinging load - feeds back and the boom oscillates. Efficiency is traded directly against stability.

Stability. The valve needs a larger pilot pressure change to move, so it is far less sensitive to circuit compliance and load oscillation. The cost is that the system must generate higher pressure on the opposite side simply to lower the load, which is energy turned into heat.

It is a counterbalance valve with the pilot ratio treated as the primary selection variable, configured for duty where the load varies widely - cranes and articulated booms in particular. The hydraulic principle is the same; the selection emphasis and the ratios offered are what differ.

The pilot ratio first, since too high a ratio is the usual cause, then hose compliance between valve and cylinder and the counterbalance pressure setting. Fitting a lower-ratio valve often solves it directly where adjusting settings has failed. It is worth trying that before assuming the cylinder or pump is at fault.

Because the pressure the valve holds back changes enormously between an empty hook and a rated load, and the boom geometry changes it further through the arc. A ratio that behaves well at one load can be unstable or unable to open at another, so the variation must be considered when selecting.

On the cylinder port, as with every holding valve, so a hose failure cannot release the load. On crane and boom equipment this is normally a statutory expectation as well as good practice, and the valve is often integrated into a block bolted to the cylinder.