Abstract: A safety valve is mounted on an underwater oil well and is remote-controlled from a central control station. The control station is connected to a receiving station, where the valve is disposed, via a single small-section hydraulic line which feeds, at a low rate of flow, a hydropneumatic accumulator for supplying an operating jack of the valve. A manostat switch at the receiving station controls a feed/bleed hydraulic relay of the jack in dependence on the pressures measured in the line at the receiving station. The invention finds application in oil valve safety operations.

Abstract: In the gas shortage detection device of a piston-type hydropneumatic accumulator, a control rod slidably mounted in the cylinder head on the gas side is displaced under the action of the thrust exerted by the piston when this latter comes closer to the cylinder head than a predetermined distance. A flexible motion-reversal coupling element such as an inextensible cord which works in traction and has a predetermined dead range of travel is placed between the piston and the sliding rod.Correct performance of the detection device can thus be checked by partial draining of the oil compartment, the detection device being triggered into operation when the piston comes close to the bottom end of the cylinder.