| 摘要 |
<p>To control the flow of a fluid from an environment to a vacuum source, a device including a piston (2) is mounted in the path of the fluid. The path is not vented so that the mass of fluid entering the device is equal to the mass exiting the device. The piston (2) is mounted so that it may constrict the path at a constriction point (5), and so that it may move in a direction (14) transverse to the flow the fluid at the constriction point (5). The frontal face (15) of the piston (2) is exposed to the fluid in the path, and the distal face (16) of the piston (12) is exerted on the piston (2) so as to tend to widen the path at the constriction point (5).</p> |
