Gas pressure regulator

A gas pressure regulator comprising, in a body having a main direction with opposite end portions and lateral sides, a first cavity and a second cavity separated by a partition wall having a through passage, a piston means arranged in the second cavity and secured to a hollow rod sealingly slidingly extending in the through passage, whereby a first chamber and a second chamber are delimited in the first and second cavities by the partition wall, respectively, a third chamber being delimited in the second cavity by the piston means and communicating with the first chamber by the hollow rod, said hollow rod having an end portion forming a valve member movable in the first chamber and adapted to cooperate in contact engagement with a valve seat carried by a closure member mounted in the body and closing externally the first chamber, an inlet means connectable to a source of gas under pressure and in fluid flow communication with the first chamber, an outlet means in fluid flow communication with the third chamber, and a fourth chamber formed in a lateral side of the body, opening outwardly and closed outwardly by an impervious flexible wall and in fluid flow communication with the second chamber, the second and fourth chambers filled with a substantially incompressible fluid.