Fluid handling – Ambient condition change responsive – Underwater
Patent
1992-09-21
1994-10-25
Rivell, John
Fluid handling
Ambient condition change responsive
Underwater
1372361, 251 3001, 251 61, 251 62, F16K 1736
Patent
active
053579992
DESCRIPTION:
BRIEF SUMMARY
This invention relates to control systems and apparatus for opening and closing valves on subsea installations associated with oil and gas production from subsea locations.
The Prior Art
Hitherto, subsea valves have been operated manually by divers, power operated by manned or unmanned submersible vehicles, or remotely actuated by means of integral valve actuators and control systems utilising mineral oil or specially formulated water-based solutions as the power fluid.
The remotely actuated systems are to a large extent versions of conventional surface equipment adapted for marine use and they have the disadvantage that to provide reliable operation in an environment of corrosive seawater which contains particulate matter and fosters biological activity, it is necessary to isolate internal components from seawater and utilise specialised power fluids with correct levels of additives. These power fluids tend to be expensive and the additives, or base constituents, often are environmentally deleterious. A further disadvantage of existing systems is the need to supply, or resupply, suitable power fluids. These drawbacks have inhibited the development of subsea closed loop control systems.
SUMMARY OF THE INVENTION
The aim of the present invention is to eliminate, or at least substantially alleviate the drawbacks of the prior art subsea valve actuators, and in accordance with the invention there is provided a subsea actuator for operating a subsea component such as a valve or similar linearly operated device, comprising a housing, a movable wall member cooperating with the housing to confine therewith a substantially closed chamber separated by the movable wall member from another fluid space, the wall member being fastened to an elongate output member and being movable under forces acting against the opposite sides thereof to displace the output member longitudinally, and inlet means to connect the chamber to either a source of pressurised fluid at a pressure greater than the hydrostatic pressure of the ambient seawater, or to drain outlet at a pressure not greater than the hydrostatic pressure of the ambient seawater, the actuator being arranged for the other space to be at the hydrostatic pressure of ambient seawater and the movable wall to be moved in a forward direction when the chamber is connected to the source of pressure fluid and to be moved in a reverse direction when the chamber is connected to the drain outlet.
A control system based on an actuator in accordance with the invention may use untreated seawater and a pressurised fluid preferably obtained from a subsea source and possibly also untreated sea water as the power mediums, whereby the sea-bed hydrostatic pressure at least contributes to the production of a force acting on the movable wall member to displace it, such as for actuating a valve. The pressurised fluid may be a low density fluid (gas), seawater pumped to a pressure above the ambient hydrostatic pressure of the actuator or could be taken from a well stream to which the valve being controlled is fitted. The control system will include a valve for selectively connecting the chamber of the actuator to the source of pressurised fluid or to a drain. When seawater is utilised as the pressure fluid the drain can lead directly to the surrounding seawater, but in this case the actuator will require an additional component such as a spring for driving the movable wall to produce a rearward stroke of the output member as the movable wall will be exposed to the hydrostatic pressure of the ambient seawater on both sides. The pressurised fluid can by a low density fluid, including gases. If gas is used as the pressurised fluid, the drain may be led to a level above the sea surface, preferably via a closed pressure chamber to accelerate actuator operation, so that the seawater pressure in the other space may be solely responsible for the rearward displacement of the movable wall member when the chamber is connected to the drain.
The other space, which is preferably another chamber in the h
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Dowdall Dennis S.
Loth William D.
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