| 摘要 |
A well safety valve having a piston and cylinder assembly which is connected to and actuated by a hydraulic control line extending to the well surface for moving the valve to an open position in which the hydrostatic head in the control line is balanced by a fluid column exposed to the opposite side of the assembly acting to close the valve. The fluid column has a greater density than the hydraulic fluid in the control line for biasing the valve to the closed position. The volume of fluid in the fluid column is greater than the volume of fluid in the control line whereby exposure of the fluid column to gas will not substantially change its density. The housing includes a container in communication between the other side of the assembly and the fluid column and contains a grease for protecting the assembly. The grease has a density less than the density of the fluid column and is of a volume greater than the volume displaced in the assembly upon actuation of the piston and cylinder.
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