| 摘要 |
A gas control device for controlling the gas supply to the burner of a domestic hot water boiler has two main valves arranged in series in the gas flow path so as when closed to define a chamber between them. A second chamber is communicable with this chamber through an auxiliary valve which is open when the main valves are closed and closed when the main valves are open. A shut-off valve is responsive to the pressure in the second chamber so as to close the flow path if gas leaks through the upstream main valve when supposedly closed. The subsequent closing of the auxiliary valve when the main valves are later opened maintains the pressure in the second chamber so that the shut-off valve remains closed.
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