Control of sub-surface safety valve

Apparatus is for the surface control of a sub-surface safety valve set within the production tubing of a drilling well. The apparatus comprises a hydraulic actuator 1 for opening the sub-surface safety valve, a control line 3 for supplying hydraulic control fluid to the actuator and a first control valve 7 for controlling the supply of hydraulic fluid to the control line. A non-return valve 15 in the control line path, between the actuator and the control valve, prevents any contaminants entering the hydraulic fluid at the actuator from reaching the first control valve by migration up the control line. An exhaust line 9 connects the actuator and control line and an associated second control valve 11 enabling flushing of fluid from the actuator and control line to a vent 12. The apparatus can also be used to check for leakage from the actuator using pressure sensor 14.