| 摘要 |
<p>An electropneumatic control device selectively operable to allow manual operation of a double-acting piston-cylinder arrangement (38) or to supply pneumatic fluid to operate said arrangement, in which the control device comprises: a pair of pneumatic switching valves (20, 21) coupled one each with a respective chamber (36, 37) of said double-acting piston-cylinder arrangement; an electrically operated valve (12) coupled with a pressure source of pneumatic fluid and coupled by pressure lines selectively with one or the other of said switching valves; a pair of throttles (34, 35) provided one in each of said lines; and a pair of venting arrangements each coupled with a respective chamber of said piston-cylinder arrangement via a corresponding one of said switching valves, each venting arrangement including an unthrottled connection to atmosphere and a throttled connection (62, 63) to atmosphere, and the arrangement of the device being such that operation of the electrically operated valve in one mode connects said pressure source via one of said switching valves and corresponding throttle to one of said chambers and the other of said chambers is coupled with the venting arrangement which is coupled with the other of said switching valves in such a way that the initial movement of the piston of said piston- cylinder arrangement, caused by pressurisation of said one chamber, causes said other chamber to be vented to atmosphere via the respective unthrottled connection and then during the end portion of the piston movement said other chamber is vented to atmosphere via the respective throttled connection in order to damp the final movement of the piston which is sensed by devices 44, 45. <IMAGE></p> |
