The invention relates to a fluid control device (500) for treating a well, said device comprising: a piston (550) translatably mounted in said chamber (320) and releasable immobilization means (900) capable of rupturing, on which, in an initial state, one end (552) of the piston (550) comes into abutment and which, in an initial position, close the pipe associated with the annular space (350), the immobilization means (900) being releasable under the influence of the fluid pressure in the chamber (320) which is equal to the fluid pressure in the liner (100), a closure member (514) translatably mounted in said chamber (320), configured to open or close the communication pipe (316) with the inside of the casing (200), said closure member being, in the initial state, in contact with another end (554) of the piston (550) which holds it in the open position.