A valve assembly for controlling fluid communication along a well tubular, the valve assembly comprising: a hydraulically operated valve comprising a valve member which is movable between an open position in which the valve member permits fluid communication along the well tubular and a closed position in which the valve member restricts fluid communication along the well tubular, and a hydraulic actuator associated with the valve member for moving the valve member between its open and closed positions; a control system for selectively controlling the flow of hydraulic fluid to and from the hydraulic actuator, to operate the valve; characterised by: a vent chamber operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position; and a vent conduit operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position, the vent conduit being exposed to fluid external to the valve assembly at the prevailing external pressure; in which the control system has a first valve closing state in which the vent chamber is isolated from the hydraulic actuator and hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented to an exterior of the valve assembly through the vent conduit; in which the control system has a second valve closing state in which hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented into the vent chamber; and in which the control system is configurable in a selected one of the first and second valve closing states according to an operating requirement of the valve. a hydraulically operated valve comprising a valve member which is movable between an open position in which the valve member permits fluid communication along the well tubular and a closed position in which the valve member restricts fluid communication along the well tubular, and a hydraulic actuator associated with the valve member for moving the valve member between its open and closed positions; a control system for selectively controlling the flow of hydraulic fluid to and from the hydraulic actuator, to operate the valve; characterised by: a vent chamber operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position; and a vent conduit operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position, the vent conduit being exposed to fluid external to the valve assembly at the prevailing external pressure; in which the control system has a first valve closing state in which the vent chamber is isolated from the hydraulic actuator and hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented to an exterior of the valve assembly through the vent conduit; in which the control system has a second valve closing state in which hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented into the vent chamber; and in which the control system is configurable in a selected one of the first and second valve closing states according to an operating requirement of the valve. a vent chamber operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position; and a vent conduit operatively connectable to the hydraulic actuator, for selectively receiving hydraulic fluid that is exhausted from the actuator when the valve member is moved to its closed position, the vent conduit being exposed to fluid external to the valve assembly at the prevailing external pressure; in which the control system has a first valve closing state in which the vent chamber is isolated from the hydraulic actuator and hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented to an exterior of the valve assembly through the vent conduit; in which the control system has a second valve closing state in which hydraulic fluid that is exhausted from the actuator during movement of the valve member to its closed position is vented into the vent chamber; and in which the control system is configurable in a selected one of the first and second valve closing states according to an operating requirement of the valve.