| 摘要 |
<p>A backflow preventer comprising a body defining a passage for flow of liquid between a supply pipe and a service pipe, a check valve in the body passage, and a relief valve assembly connected to the body passage downstream of the check valve, the assembly comprising a liquid drainage passage connected to a first port in the body passage, a first valve in the drainage passage, a gas intake passage connected to a second port above the first port in the body passage, and a second valve in the intake passage.</p> |
