Stable operation of the LS distributor in conjunction with the counterbalance valve in lifting equipment

There is a crane equipped with an LS system distributor featuring post-compensation and an unregulated pump (a compensator is installed in the pressure section of the distributor). The hydraulic cylinder that raises and lowers the crane's boom has a one-way counterbalance valve (the valve is installed in the piston chamber). When a small flow is supplied to the rod chamber of the cylinder (slow lowering), the crane's boom begins to oscillate with gradually increasing amplitude during descent. This occurs both with and without a load. The Parker training manual states that for stable operation of counterbalance valves with LS systems, fine-tuning of the system is required, but it does not specify what exactly needs to be adjusted. If the opening pressure of the counterbalance valve is adjusted, increasing the setting leads to greater oscillation, while decreasing it slightly reduces the oscillation but does not eliminate it completely. The same Parker manual mentions that the setting of the counterbalance valve should be 30% higher than the setting of the main relief valve in the system. What else can be adjusted in the LS system and counterbalance valve to achieve stable operation of this system? The flow from the unregulated pump is 70 liters per minute, the flow through the distributor spool is about 5 liters per minute, the opening pressure of the compensator in the pressure section of the distributor is 21 bar, and the counterbalance valve is set to 325 bar, with a pilot ratio of 4.25:1.

Making adjustments to a counterbalance valve can be a hazardous/dangerous process.  Caution MUST be taken!  Given the variations within the counterbalance valve adjustment mechanism, load sense circuits, pump controls, as well as directional control valve variations, to ensure a proper working system, IFPS recommends checking with the original manufacturer/OEM before making any adjustments.  Interaction between the components may be present.  Specific machine safety precautions may be necessary during any adjustment process.  Any adjustments should only be attempted by trained personnel