| 摘要 |
The modifying method comprises the steps of attaching appropriate magnetic material to a part of the valve which moves when the gate of the valve moves. A first magnetically operable sensor is fixedly mounted relative to the valve, externally of a valve chamber of the valve, wherein the first sensor is mounted in a housing and wherein the housing includes a second sensor for sensing if a lid of the housing is opened.- A signal emitting alarm is connected to the first sensor, the mounting of the first sensor being at a position where it will cooperate with the appropriate magnetic material such that when the valve is open, no signal will be emitted but when the valve is closed, a signal will be emitted, the first sensor being of the type which does not require power to be supplied to it to place it into a magnetic sensing condition for use
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