| 摘要 |
<p>The apparatus is a three ported valve assembly with a first port (16) in communication with a vacuum source, a second port (14) in communication with a process vacuum, and a third port (20) in selective communication between atmosphere and the process vacuum. Communication between the first and second ports is regulated by the position of a piston (24). Moreover, when the piston reaches its lowermost position, the third port is opened to provide communication between atmosphere and the process vacuum. The position of the piston is changed by rotation of a rotary air motor (68) which, by way of a rotating beveled pinion gear (58) which meshes with two symmetrically opposed beveled idler gears (53, 54) which are journaled for rotation on a threaded trunion and which further mesh with a stationary beveled pinion gear (44), rotates the threaded trunion to raise or lower a threaded rod (40) which is coupled to the piston.</p> |
