| 摘要 |
A valve actuator includes a hydraulic cylinder with a pair of pistons separately, slidably mounted therein for movement between a first end and a second end of the cylinder. An actuator rod is joined to a first of the pistons to extend through an opening in the first end of the cylinder to terminate exterior thereto and be capable of being joined to a valve stem. A high pressure gas accumulator is mounted on the cylinder to locate the second end thereof within the accumulator. The second end of the cylinder has an end closure with access therethrough to allow communication between the interior of the accumulator and a first side of the second piston of the pair. Normally, hydraulic oil is supplied to the cylinder to act on the first piston thereby causing both pistons to move axially against the high pressure gas of the accumulator which, in turn, axially moves the pistons when the hydraulic fluid is discharged. A tubular housing extends from the end closure through the accumulator to be terminated outwardly thereof. A hollow tube extending from the second piston into the tubular housing makes sliding, sealed contact therewith to allow communication from the tubular housing to a space between the pistons. Providing hydraulic fluid to the tubular housing introduces such fluid to the space between the pistons allowing the first piston to be axially moved as the second piston remains against the end closure. |
