| 摘要 |
PROBLEM TO BE SOLVED: To prevent electric sparks from occurring by changing over an air flow path from a pneumatic source using liquid level detectors which detect upper and lower limit positions of liquid chemical in a storage tank to open/ close a pneumatic open/close valve. SOLUTION: A pneumatic open/close valve 4 is placed in a transfer pipe 2. Liquid level detectors 8a, 8b are used to detect a lower limit liquid level position and an upper limit liquid level position in a storage tank 1. An air switch circuit mechanism 9 opens/closes the pneumatic open/close valve 4 based on the upper and lower limit liquid level positions detected by the detectors 8a, 8b. The valve 4 opens/closes by a change in pressure of air compressively fed from a pneumatic source G to control transfer of liquid chemical from a liquid chemical supply part 5 to the storage tank 1. Since the pneumatic open/close valve 4 which can be opened/closed by air pressure instead of electricity is thus employed, even if volatile gas of volatile liquid chemical L in the storage tank 1 leaks out, danger of ignition or explosion due to electric sparks or the like can be prevented.
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