| 摘要 |
Apparatus for detecting the presence of a web material at a given location, including a movable member at the location, having a conduit therethrough, and pressure fluid means cooperating with the movable member for discharging through the conduit when no web material is present at said location and for building up pressure behind the movable member, for urging the latter against the web material when the web material is present at said location. Sensing means cooperate with said fluid pressure means for detecting such build up of pressure.
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