Abstract: This check-valve assembly, adapted to close a fluid flow circuit without creating overpressures or hammering in this circuit, comprises a tubular body (1) connected at both of its ends to a respective pipe section (2, 3), a closure member (4) mounted to be movable inside the body (1) between an open position in which the fluid may circulate in the direction of arrow F1 and a closed position in which the closure member bears against a seat (21) so as to cut off any circulation of this fluid in the direction of arrow F2. According to the invention, the closure member (4) is axially slidably mounted in the body (1) and delimits a cylinder (4a) cooperating with a fixed piston (11) so as to constitute a restraining device which becomes more effective when the closure member approaches its closed position. Simultaneously, the reverse flow of the fluid (direction F2) is progressively limited by passage in a path (24, 25) having a relatively high pressure drop.

Abstract: The device comprises at least one nozzle (T), in combination with a regulating valve (VR). A detector (135) measures the flowrate of the fluid in the nozzle and controls a distributor (109) for selecting a static pressure take-off orifice from among a plurality of regularly staged orifices in a convergent section (101). The orifice is brought into communication with a chamber (127) of the regulating valve to control the position of a closure member (119) which uncovers to a varying degree the orifices of a cage (117). The displacement of a distributor (121) from one position (R) to another (S) converts the regulating function into a shut-off function by pressure effect, by applying a high pressure to the chamber (127). The total immersion of the closure member obviates the disadvantages of the rod and packing system of conventional valves, as well as those resulting from the radiation-sensitivity of the prior art pneumatic servomechanisms.