Abstract: An electropneumatic converter controlled by solenoid valves, in which the solenoid valves are connected respectively to the feed pressure and to atmosphere, each via a pressure regulator controlled by a differential pressure measurement device connected across a respective solenoid valve, so as to maintain a constant pressure difference across the solenoid valves.

Abstract: A control system for a pneumatic valve actuator comprising three operating blocks memorizing respectively the values of the spring pressure p.sub.m, the counter-thrust pressure p.sub.c and the friction pressure p.sub.a for the various valving member position values, said blocks being connected in parallel and, via a switch, to the valving member position transducer or to the set position generator and connected to the pressure computing block connected via a second switch to the pressure generator or, together with the value read by a transducer for the pressure existing in the actuator, to a differentiator connected to two multiplier units for K and for (1-K) respectively, which are connected to the transit memory of the p.sub.c operating block and to the p.sub.a operating block respectively, the switches being driven by a logic control unit which switches over when the valving member is at rest. Means are provided for sensing anomalies and the extent of wear.