Supply circuit for a two-tube hydraulic system

A supply circuit for a hydraulic valve control system for controlling a steam control valve, comprising:

• pressure generating means for pressurizing a hydraulic fluid;
• a slide valve actuated by the fluid pressure generating means;
• main conduit means for controlling a control valve, the main conduit means being in fluid communication with the fluid pressure generating means through the slide valve, the slide valve being arranged to control a flow of fluid between the pressure generating means and the main conduit means;
• the slide valve including a slide having three control edges which cooperate with valve volumes in the slide valve to control the flow of fluid through the valve, the control edges including a first filling control edge for regulating a circuit filling operation, a second main control edge for controlling the flow of fluid during normal operation of the circuit, and a third test control edge for regulating a test stroke of the slide without disrupting the control of normal operation by the slide valve, wherein the main control edge remains closed to the main conduit during the filling operation until an operating pressure in attained in the circuit and remains open during the test stroke;
• a plate valve in fluid communication with the slide valve, the plate valve acting as an outflow amplifier for moving the slide to close the main control edge;
• and,
• a safety deactivation unit in fluid communication with the pressure generating device, the slide valve, and a fluid outflow for controlling the pressure in the slide valve and main conduit means and for activating the test stroke.