| 摘要 |
To control the flow of air from a process chamber, such as a clean roam, to an exhaust, a movably mounted piston (5) that is attached to a movably mounted gate (96, 961) is disposed adjacent to the flow, so that the flow passes immediately over the frontal face (52) of the piston. The distal face (51) of the piston is expos ed to a reference pressure, preferably the pressure of the process chamber. The gate is mounted so as to variably impede the flow downstream of the frontal face of the piston. A restoring force, preferably the weight of the piston and the gate, tends to move the piston so as to lessen the gate's impedance on the flow.
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