| 摘要 |
A main valve (1) is connected into a pressurized water pipe for an irrigation installation and has a valve body (4) formed as a differential piston and with a through bore (5), said body being operated in both directions by means of the water pressure, the piston (4) in one end position closing the water pipe and in its other end position keeping it open. The piston (4) is guided to said end positions by means of a control valve (7) arranged to open or close a duct (6) starting from the major cylinder bore, thereby to cause the water present to actuate the piston (4). The control valve (7) is in turn controlled by rainfall onto, and evaporation from an upwardly open bowl (8), and a drop means (9) active during irrigation. The bowl (8) is part of a tipping means with two tipped end positions, controlled by the quantity of water in the bowl (8). To achieve operation of the main valve (1) such that irrigation substantially takes place at night, and that the length of time between irrigation can be varied, the tipping means is supplemented by a closed air chamber (15) on the other side of the pivoting shaft (35), said chamber and bowl (8) having a common flat bottom (16) and mutual communication via a slit (17) at the bottom. By the volume change in the air enclosed in the air chamber (15), caused by the temperature difference between night and day, the quantity of water contained in the open bowl (8) and in the chamber (15) is displaced at night such that the tipping means tips over into a position opening the main valve (1). |
