| 摘要 |
A pneumatic actuator and method for a gate valve are disclosed which provide for stepped guide connections between upper and lower cylinder plates for a pneumatic cylinder to thereby automatically centralize and locate the relatively heavy pneumatic cylinder and upper/lower plates with respect to each other to increase the speed and ease of the assembly of the pneumatic actuator. Each major metallic sliding component of the actuator is mounted on a wear ring that prevents metal-to-metal contact to thereby prevent friction wear and galling. A wear ring is provided in the operator stem packing assembly that provides for more reliable sealing due to lack of wear on the operator stem in the region of the stem packing wherein the operator stem reciprocates. A smaller diameter spring housing is provided to house that portion of the spring assembly that extends beyond the stroke of the piston to reduce cost of the larger diameter pneumatic cylinder. A slip joint is provided between the driving stem and operating stem to permit removal/assembly of the actuator components at bolted connections between the upper cylinder plate, pneumatic cylinder, and the lower cylinder plate as well as between the spring housing and the bonnet. This assembly permits the most direct access to any seal or packing to reduce maintenance time. The diameter of the pneumatic actuator is preferably in the range of about twenty inches to allow a single size actuator that operates on virtually any normally available site pressure. The construction permits interchangeableness of components to reduce manufacturing costs when variations in size of certain components are made to conform to particular specifications. The actuator is designed so that it can be constructed and assembled entirely separately from the gate valve to thereby allow reduced manufacturing costs due to manufacturing scheduling flexibility.
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