To prevent backflow caused by siphon action, prevent clogging with foreign matter, and increase versatility, simply and at a low cost, by sensing change of pressure difference between two points generated by change in flowing direction in a supply pipe formed in a shape of a siphon to open and close an opening/closing valve for introducing outside air.
A pressure chamber (i) of an opening/closing valve 5 is communicated to a pressure intake (i') of a supply pipe 4 formed in a shape of a siphon. When liquid is fed from the supply pipe 4, that is, at a time of direct flow, internal pressure of the pressure chamber (i) exceeds internal pressure of a pressure chamber (j) communicated to the other pressure intake (j'). Therefore, a pressed plate 13 which is sandwiched between the pressure chambers (i), (j) deflects toward the pressure chamber (j) to make a valve element 15 seat a valve seat 12. On the other hand, when the feeding of liquid from the supply pipe 4 is stopped, the internal pressure of the pressure chamber (i) exceeds that of the pressure chamber (j). The pressed plate 13 deflects toward the pressure chamber (i) to make the valve element 15 separate from the valve seat 12. As a result, outside air is introduced into the supply pipe 4 through an outside air intake port (c), a valve chamber (d), and each communicating passage (e) to cancel siphon action, resulting in preventing backflow.
YOKOTA HIROSHI
TANIMOTO TETSUYA
OKIMOTO TADASHI
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