Typical Problems and Potential Solutions

The problem this creates is that the opening on the counterbalance valve is so small that it is very difficult for it to modulate and will have a tendency to open and close at a high frequency causing unstable movement of the actuator.

To help overcome this problem Sun has developed Restrictive and Semi-restrictive cartridges that fit into the standard series cavities but have reduced area flow paths on the nose end of the cartridge. This means that at lower flows there is a greater opening of the cartridge and therefore the valve modulates better and is less likely to be unstable. The reduced area does mean an increase in pressure drop with flow and therefore this may cause a problem at higher flows. As an approximation the pressure drop with the semi-restrictive cartridges is the same at half the rated flow compared to the standard cartridge, while the pressure drop with the restrictive cartridge is the same at a quarter of the rated flow compared to the standard cartridge.

These cartridges are available on series 1,2 and 3 but are most commonly used on series 1. The semi-restrictive cartridges can also help on general unstable operation because the additional pressure drop creates greater stiffness in the circuit.

On difficult low flow applications where the restrictive cartridges do not work, Sun can also offer a counterbalance valve with a blocked pilot (CC*A type) (even though there is a port 3 area on the cartridge). This now becomes a load control valve without a pilot, creating a continuous back pressure so it is less efficient but unlikely to be unstable. This valve can also be used effectively on applications where the load is constant so that there is no real advantage having an external pilot.