Hydraulic actuator controls

In combination with hydraulic actuator means, a device for controlling the flow of fluid to said hydraulic actuator means, said device comprising a fluid pressure operated main valve for regulating the fluid flow to the actuator means via service lines;

• a pilot valve for controlling the main valve via control lines, said pilot valve including electrical operating means;
• electrical input means for an electrical input signal;
• flow sensing means for producing an electrical feedback signal dependent on the rate of fluid flow to the actuator means, said flow sensing means including a pivoted movable element displaceable from a closed flow blocking position in accordance with the fluid flow to be sensed and biased onto said position by biasing means and mechanical/electrical transducer means for converting such displacement into said feedback signal;
• and means for comparing said feedback signal with said input signal to produce an electrical error signal for said electrical operating means to operate said pilot valve in accordance with such comparison, said input and feedback signals being of opposite polarity and said comparing means comprising an adder;
• a failsafe clamp for preventing said first-mentioned error signal reaching said pilot valve and an error signal integrator for integrating said first-mentioned error signal to operate said failsafe clamp in the event that such error signal does not decay;
• said electrical input signal means including means for varying said electrical input signal in opposite directions from a null value to determine the direction of operation of said main valve, said flow sensing means being installed in one of the supply and return lines to the main valve and switch means being responsive to the direction of fluid flow in said control lines from the pilot valve to the main valve being provided for determining the polarity of said first-mentioned electrical feedback signal.