| 摘要 |
A double valve arrangement is installed in intermittently operating vacuum filter apparatus in a pipeline connecting the filter means to a vacuum source to vent the line to atmosphere whenever the vacuum is shut off. This valve arrangement comprises a pipe section provided with a lateral opening, connected to the filter means, and with internal mutually facing annular shoulders disposed at respective sides of the lateral opening, and a piston-mounted sealing disc which is of smaller diameter than the pipe section and is reciprocable inside same to abut sealingly the one or the other of the shoulders and thereby bring the lateral opening into communication with the respective opposing end of the pipe section, which is connected, respectively, either to the vacuum source or to atmosphere. An annular gap is always present between the peripherly of the disc and the internal surface of the pipe section so that movement of the disc, e.g. at a frequency of 5 to 20 cycles per minute, is not impeded by rubbing.
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