It is conventional to use a subsurface well safety valve as disclosed in U.S. Pat. No. 4,161,219 which is controlled by a hydraulic control line extending through the well surface. Such a safety valve may be positioned hundreds or even thousands of feet below the well surface and is designed to be operable for many years. However, debris may become trapped in the hydraulic control line such as when making up the connections, scale flaking off of the inside of the control line, or sediment in the control fluid settling out of the control line. In such instances, the debris would settle out on the hydraulic piston and cylinder assembly in the safety valve and possibly interfere with its operation.
The present invention is directed to the combination of a hydraulic filter with a safety valve for filtering the hydraulic fluid at a position adjacent the safety valve for reducing the possibility of debris accumulating upon the hydraulic piston and cylinder assembly. The hydraulic filter may be provide as a part of the safety valve, or in a separate tubing sub above the safety valve or as an attachment which may be connected to the outside of the production string.