| 摘要 |
The mechanism has an actuation piston (19) which is in a power transmitting connection with the valve stem (4) in opening direction. The piston (19) includes two unevenly sized piston parts (20, 21) which together with appropriate parts of the mechanism's cylinder (5) define two work chambers (24, 23). In both chambers the effective piston area is positioned against the valve's opening direction. When the valve is closed, the one piston part (20) blocks an exit port (13) from the first work chamber (24), and an entry port (13) connects, possibly through a non-return valve (37), to the other work chamber (23) and from this through a passage (26) in the cylinder (5) to the first work chamber (24). Supply of pressure fluid to the entry port (13) initiates via the piston (19) the opening movement of the valve. After a certain piston stroke a cut-off (32) releases on the first piston part (20) the exit port (16) and at the same time the passage (26) is blocked by another cut-off (33) on the piston. Pressure is hereby relieved in the first work chamber (24), after which hydraulic pressure alone works on the lesser piston area in the second work chamber (23). In such a way a gradual reduction of opening force is achieved and with it a reduction in the use of pressure fluid.<IMAGE>
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