Subsea control systems and apparatus

摘要

PCT No. PCT/GB91/00490 Sec. 371 Date Sep. 21, 1992 Sec. 102(e) Date Sep. 21, 1992 PCT Filed Mar. 28, 1991 PCT Pub. No. WO91/15692 PCT Pub. Date Oct. 17, 1991.A subsea actuator for operating a valve (20) or the like comprises a movable wall member (19) fixed to an axially slidable stem and separating a pressure chamber (2) from a space (3) which is subjected to the hydrostatic pressure of ambient seawater. A selector valve (11) is operable to connect the chamber (2) to a source of pressurised fluid, e.g. a source of pressurised gas (14), or to a drain e.g. connected to atmosphere by a pressure vessel (12) and pipe (15). A blowdown valve (16) and dump valve (13) are provided for ejecting liquid collected in the vessel (12). The space (3) may be connected to an open-bottomed container (17) to provide a gas barrier between the seawater and the interior of the actuator. Supply of pressurised gas to the chamber (2) causes the member (19) to be driven forwards, gas being allowed to flow past the member into the space (3) during this movement to assist the expulsion of water from the container (17) and the expulsion of any contaminants from within the actuator. When the chamber (2) is connected to atmospheric pressure the hydrostatic pressure of the seawater causes the member (19) to be driven in the reverse direction.