Pilot type on-off valve and backflow prevention device having the same

摘要

PROBLEM TO BE SOLVED: To provide a pilot type on-off valve capable of being more easily and more inexpensively manufactured than the conventional one, and excellent in backflow prevention performance.SOLUTION: A bleed valve element 6 of a pilot type on-off valve V1 is constituted by using a flexible plate-like or sheet-like member, and has a through hole, and a cylindrical protrusion part 56 having one end side opening part 51a of a pilot hole 51 is inserted into the through hole, and thus, attachment to a diaphragm plate 5 can be achieved. A part of the bleed valve element 6 faces a back pressure chamber side opening part 52a of a bleed hole 52, and is brought into contact with or separated from the vicinity of the back pressure chamber side opening part 52a in accordance with pressure in a primary side water flow passage 11 and the bleed hole 52, and the back pressure chamber side opening part 52a can be opened and closed.