With a Control Box for a Fail Safe Control Valve Single Acting Control box it is possible to position the valve from 0 to 100% at any desired setting. This box is always used for a control valve, which has a spring in the actuator to go to the safe situation in case of a shutdown at all time (Normally Close or Normally open). In case of loss of hydraulic and electrical power the valve will go to the safe position.
Normally the spring in the actuator will at all time force the valve to go to safe situation, but with two solenoid valves and flow restrictions the valve can be opened or closed at a certain speed and set at the required position. The positioner on the valve will give feedback of the actual position of the control valve. Important is to have a comparison of the setting and feedback not 100% equal, otherwise the unit will respond very nervously and consume a lot of hydraulic fluid.
