| 摘要 |
PURPOSE:To prevent lubricating oil from penetrating into an actuating chamber by installing a discharge port for sealing shaft seal gas in a screw seal of a vacuum pump. CONSTITUTION:When a screw vacuum pump is in a stationary operation state, an actuating chamber 24 is in a vacuum and there is a large pressure differential in a gap with an oil chamber 23. At this time, if a proper amount of shaft seal gas is made to flow from a discharge port 22, this shaft seal gas flows into the side of the oil chamber 23 by pumping action of a screw seal 20, thus oil prevented from penetrating into the actuating chamber 24. A floating seal 19 checks the shaft seal gas flowing into the actuating chamber 24 to a small quantity. On the other hand, in a transit operation state such as at time of starting, when the shaft seal gas is in a state of being liable to flow into the actuating chamber 24, the screw seal between the discharge port 22 and the floating seal 19 works to put the shaft seal gas back, so that an increase of the shaft seal gas flowing into the actuating chamber 24 is checked to a small quantity and, what is more, oil penetration into the actuating chamber 24 due to an ejector effect of the shaft seal gas is prevented, thus a stable shaft seal effect is securable.
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