| 摘要 |
A device for adjusting the degree of vacuum in an apparatus for collecting substances by suction, comprising a valve that is provided with an air flow port connected to the atmosphere at one end and to a chamber at the other end, the chamber being connected to a source of vacuum and to the apparatus, and the port comprising a flow control element that is adapted to be attracted into the closed position by the action of a permanent magnet supported in the body of the valve in an adjustable position.
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