BACKWARD FLOW PREVENTION VALVE AND WATER HEATER INCLUDING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a backward flow prevention valve ensuring excellent durability for a long period of time.SOLUTION: A backward flow prevention valve comprises: a valve case 4 having a primary opening 2 and a secondary opening 3; a valve element 5 provided in the valve case 4 and closing or opening the primary opening 2; a valve seat 6 provided at the primary opening 2, the valve element 5 abutting on the valve seat 6; and an elastic element 7 urging the valve element 5 from the secondary opening 3 toward the primary opening 2. The valve element 5 is formed out of a resin material and a surface roughness of an abutment portion 5a of the valve element 5 on which the valve element 5 abuts on the valve seat 6 is set different from that of the valve seat 6. Even if an excessive pressure is generated in the secondary opening 3 or the backward flow prevention valve is used in an environment in which a heat load is applied to the valve, it is possible to exhibit a backward flow prevention function for a long period of time.