| 摘要 |
A noiseless unitary apparatus to retain small and large size record sheets in selected fixed positions on different parts of a perforated surface of a vacuum chamber by providing a wall within the chamber that No. 1 divides the chamber into two vacuum areas and that No. 2 has a restricted air passageway formed therein to reduce the flow of air between one vacuum area and the other while it is being drawn by a vacuum impeller through any of the perforated surfaces that are not covered by one of said record sheets.
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