| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a decompression type backflow preventer having greatly reduced pressure loss, compared with a device in a prior art, for reliably closing a relief valve in an intermediate chamber during the flow of water. <P>SOLUTION: In a first check valve, a narrow flow path part 68 (a first portion of an intermediate flow path) having a small flow path area, formed between a circular portion 46 of an outer periphery 45 of a supporting member and a second diameter enlarged portion 12 of a casing, is communicated with a back pressure chamber 39 defined in the supporting member by the back face of the head of a valve element via a communication passage 67 consisting of a clearance 66 between the outer periphery of the valve element and the inner periphery of a large diameter portion and a groove 27 formed in the back face of the head of the valve element. Thus, the low static pressure of water flowing in the narrow flow path part is guided into the back pressure chamber to move the valve element with great differential pressure during the flow of the water, reducing pressure loss with the opening of the valve being wider than that in the prior art. At the same time, a pressure chamber 130 is defined in the intermediate chamber by using a rigid partition wall, and communicated at its high pressure side 131 with the upstream side of the first check valve and at its low pressure side 132 with the narrow flow path part. Thus, greater force than differential pressure between the upstream side and an internal flow path 106 operates on the valve element 136 to reliably close the relief valve 135. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
