Abstract: An electro-hydraulic actuator is disclosed, particularly for use with control surfaces in aircraft. The actuator includes a regulating piston and cylinders an rapidly-operable switching valves for the positioning of the piston in the cylinder that are operated by the supplying of discrete volumes of operating fluid thereto. Switching pulses are applied to the valves by a computer, and a sensor that is responsive to each activation of the switching valves applies an answering pulse to the computer wherein a valve breakdown can immediately be recognized. The sensor may be responsive to changes in pressure and/or flow between the valves and the cylinder located at the valve body.