| 摘要 |
An automatic timer valve for irrigation plant includes a tubular differential-area piston which defines respective major-diameter and minor-diameter chambers in a hollow valve body. The chambers normally communicate through the piston to allow water to flow interruptedly from an inlet to an outlet. A build-up of back-pressure at the outlet acts against the major face of the piston and, overcoming the inlet pressure, advances the piston against a spring to cause abutment of the shutter disc and an annular shoulder. This abutment cuts off the flow, with the exception of a restricted passage, and puts the outlet into communication with a drain outlet. When the pressure in the outlet drops, the higher relative pressure at the inlet displaces the piston in a reverse stroke and uninterrupted flow recommences. |
