Abstract: A device for controlling a hydraulic actuator comprises two servo loops having in common a fluid pressure operated main valve and an electrically operated pilot valve for controlling the main valve. One of the servo loops is for flow control and contains a flow transducer for producing an electrical feedback signal responsively to fluid flow to the actuator and a comparator for comparing the flow feedback signal with a first electrical input signal. The other servo loop is for force control and contains pressure transducing means for producing an electrical feedback signal responsively to the pressure drop across the actuator and a second comparator for comparing the force feedback signal with a second electrical input signal.

Abstract: A flow sensor for producing an electrical signal dependent upon fluid flow has a housing insertable in a bore extending transversely to and intersecting a flow passage in a port plate. A flap pivoted to the housing about an axis transverse to the flow passage is biassed by spring means into a resting position in which the flow passage is obturated. Pivotal movement of the flap from its resting position by fluid flow in the flow passage is converted into an electrical signal by a transducer, such as a potentiometer whose slider is coupled to the flap.