| 摘要 |
A valve body is formed in two half sections which are secured together to define a drain line passage and to confine therebetween a thin gate valve blade for movement between a lower open position and an upper closed position. An actuator includes a flexible bellows sealed to the valve body above the passage and a top plate connected by a rod to the valve blade. The valve body and the bellows define an expandable fluid chamber connected by a bottom port or line to the drain line. The valve body is installed within a sewage drain line extending under a floor. In the event sewage water backs up within the drain line, air within the fluid chamber is compressed to expand the bellows upwardly for closing the valve. When the sewage water flows from the drain line, the air pressure reduces, and the bellows collapses downwardly due to the weight of the top plate and automatically returns the valve blade downwardly to its open position.
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