| 摘要 |
PROBLEM TO BE SOLVED: To provide a decompression type backflow preventer which can check certainly a backflow and can adjust the pressure on the secondary side. SOLUTION: An intermediate chamber 3 is provided between the primary side passage 1 and secondary side passage, and a first check valve 4 is installed so as to check the flow from the chamber 3 to the primary side passage 1 while a second check valve 10 is installed so as to check the flow from the secondary side passage 2 to the chamber 3, and a safety valve 12 is furnished to exhaust the fluid from the chamber 3. A diaphragm 13 is interposed between the primary side passage 1 and intermediate chamber 3, and when the differential pressure obtained by subtracting the pressure in the chamber 3 from the pressure in the passage 1 is positive, the diaphragm 13 is pressed in the direction that the safety valve 12 is closed. At least either of the first 4 and the second check valve 10 is equipped with a valve element 4, spring receptacle 6, a coil spring 5 interposed between the element 4 and receptacle 6, and an adjusting bolt 7 to move the spring receptacle 6 in the axial direction of the coil spring 5.
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