Stability of a hydraulic counterbalancing system of a hydraulic winch

In hydraulic winch systems control of gravity load during lowering is achieved by incorporating counterbalance valves. The amount of opening of a conventional counterbalance valve is controlled by pressure in the supply line, thus when the load is trying to run-away it will cause pressure decrease in the motor supply line and this will reduce the amount of opening of the counterbalance valve and stop uncontrolled descent of the load. Similarly, in the event of line failure the loss of pressure in the supply line will block the uncontrolled descent of the load. As the flow through the counterbalance valve is also dependent on the pressure drop across the valve, the speed of load descent for a given opening of the valve will also depend on the load changes. Stability of the load motion is an important consideration as unstable operation of the counterbalance valve may cause load oscillations and thus affect the safety of the winch. The paper presents stability analysis of a winch system which incorporates a novel, load compensated, counterbalance valve and provides recommendation for enhancing stability of winch systems.