| 摘要 |
<p>A valve assembly is provided having a working piston (14) and seal (20) adapted to sealably engage a water flow inlet pipe (21), entering the chamber (10). This side of the piston (14) is in fluid communication with a reservoir (22), disposed above the chamber (10). The reservoir (22) is provided with a siphon tube (23) extending down outside the reservoir (22) via transfer tube (24), the outlet end of which is directed to the perforate or mesh portion (11) of the chamber (10), containing a water swellable polyacrylamide gel (12). The reservoir (22) is supplied by outlet pipe (25) leading from the chamber (10) to the reservoir (22). In dry conditions, the polyacrylamide gel (12) is in its minimum volume configuration and the piston (14) is urged away from the end of the inlet pipe (21), permitting water to enter the chamber (10). The water is forced up to the reservoir (22) via the outlet pipe (25) which then fills. When the reservoir is full, water passes through the siphon tube (23) and the irrigation outlet (28). Water from the siphoned tube (23) passes through transfer tube (24) to the perforate or mesh portion (11) of the chamber (10), hence wetting the polyacrylamide gel (12). The polyacrylamide gel (12) then expands, driving the piston (14) towards the outlet tube (21) against the bias of spring (26). At full expansion of the gel (12), the seal (20) seats against the end of the inlet tube (21) and stops flow to the reservoir.</p> |
