A valve, for example for controlling a clearance at a tip of turbine blades, includes a piston and a supply mechanism supplying fluid under pressure to cause the piston to move inside a hollow body, and a mechanism detecting a position of the piston, including a shut-off element that moves as one with the piston and is mounted such that it can move in a fluid passage between two positions, open and closed respectively, the fluid passage connecting the supply mechanism to a pressure sensor that generates an output signal representative of the position of the piston of the valve.