| 摘要 |
A non-return valve comprises a main housing 10 and an auxiliary housing 14 in which a ball 18 is entrapped. Flow can only take place from left to right and during flow the ball 18 is free to rotate causing self cleaning of its surface. The ball 18 may be pressed down to turn off the valve completely, or to partially throttle the valve, by a controllable mechanism 20 which urges a dish 24 against the ball 18. |
