Abstract: A piston-driven valve includes a valve body provided with inlet and outlet openings, the communication between which may be interrupted by a valve member which is integral with a rod connected to a piston on which a valve control pressure is exerted. The piston is located in a head mounted on the valve body and receiving a system of reset springs of the driving piston. The head includes a valve being characterized in that it includes at least one head comprising a housing with a cylindrical bore, the walls of which are provided with passages for the control fluid. The upper end of the bore is closed by a cover. The piston and its system of reset springs are reversibly mounted in the head. The head is mounted on a base which is provided with openings for the control fluid and which cooperate with the passages, so that the control pressure enters the head either under the control piston or over the control piston.

Abstract: A piston-driven valve includes a valve body provided with inlet and outlet openings, the communication between which may be interrupted by a clack-valve which is integral with a rod connected to a piston which is subjected to a valve-control pressure. A reversible head is equipped with an intake port for the control pressure, and the piston is located in the reversible head. A first reset spring named low pressure spring, directly bears on the piston, and a second reset spring is located between two calibrating bridges and selectively acts on the piston structure is provided for removing action by the second spring on the piston, in order to allow the valve to work with a low control pressure value.