| 摘要 |
<p>Actuator head for a pressure relief valve (1) having a valve element (11) spring biased to a closed position and arranged to be movable under the action of a fluid pressure medium in order to allow the escape of the fluid pressure medium through the valve for pressure relief purposes. The actuator head comprises an actuator (3) which is coupled with the valve element (11) and has a member (21) displaceable in response to fluid pressure applied thereto. A linkage (22, 19, 12) couples together the valve element (11) and the actuator (3) and has a lost-motion connection (72) which allows the valve element (11) to move against its spring biasing (13) for pressure relief purposes without imparting movement to the displaceable member (21) of the actuator (3). Biasing means (27) is arranged to oppose displacement of the displaceable member (21) of the actuator (3), and control means (4, 5) is provided to control the supply of fluid pressure to said displaceable member (21). The displaceable member (21) is arranged to be displaceable upon the application of fluid pressure to the member by said control means, so as to apply a supplementary valve-closing load to the valve element (11) via the linkage (22, 19, 12). In addition, a fail-safe mechanism is coupled with the linkage in such a way that the mechanism is movable with and forms part of the linkage during normal application of a supplementary loading by the actuator (3), but the mechanism is convertible, when the displaceable member (21) remains unintentionally in a displaced position under the action of fluid pressure and when the valve element (11) of the relief valve (1) carries out relief pressure movement, to a fail-safe mode in which the mechanism no longer forms part of the linkage (22, 19, 12) whereby no action is exerted between the actuator (3) and the valve element (11) via the linkage during the relief pressure movement of the valve element (11).</p> |
