Abstract: Apparatus for supplying gas under pressure and distributing it between a plurality, n, of outlets (15) comprises a piston (1) slidably mounted in a cylinder (2), with the piston (1) being fixed to a rod (6) which serves to position the piston in the cylinder, and with the cylinder including a base (3) provided with a gas inlet (16) and a side wall (5) having n openings, each of which is connected to a corresponding gas outlet; said piston, when in a base end postion, serving to block communication between the inlet and the outlets; the improvement wherein the openings in the side wall are constituted by grooves (13) which extend over a shorter length than the axial extent of the piston, and whose depth in the thickness of the wall increases with distance from said base, the furthest end of each groove from said base being connected to an associated gas outlet, and each groove constituting together with the piston a convergent-divergent nozzle.