| 摘要 |
<p>The retaining valve is for irrigation channels, and has a flap (3) of the same shape as the cross-section of the channel. This pivots along its top edge on a spindle (4) supported on the top of the banks (1), and in the open position lies level with the ground. The channel can be of straight trapezium-shaped section. The flap can be of the same section as the channel, or one slightly oblique in relation to it. There may be buttresses on the banks, giving continuity between the flap and banks when the flap is open.</p> |
