| 摘要 |
Water pressure in various branches of an irrigation system is controlled by incorporating a butterfly valve in each branch. Each valve is connected to its own piston-cylinder hydraulic assembly. Elongation of the assembly urges the valve toward closure. Shortening of the assembly urges the valve toward opening. A spring operatively associated with the assembly urges the assembly to shorten itself. A tube conveys actuating fluid, i.e., water, into the assembly from the conduit downstream from the valve in opposition to the force of the spring. Whenever the downstream pressure exceeds a predetermined pressure, the actuating fluid overcomes the force of the spring and elongates the assembly thereby moving the valve toward closure. This causes the valve to obstruct the flow of water, thereby returning the downstream pressure to the predetermined magnitude.
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