| 摘要 |
A backflow preventing check valve for use in a fan unit in a forced air cooling system includes a generally rectangular frame, a plurality of adjacent parallel pivot axes mounted in the frame, and a plurality of adjacent vanes that pivot around the axes between open and closed positions. The axes extend generally transverse to the direction of fluid flow through the valve, and each axis is offset from the center of gravity of its associated vane so that fluid flowing through the valve in an allowed direction moves the vanes toward the open position, and fluid flowing in a blocked direction moves the vanes toward the closed position. The axes are inclined at an angle (alpha) measured from a vertical reference, thereby causing the vanes to be urged by gravity to pivot towards the closed position.
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