| 摘要 |
<p>A low liquid level sensor in a hot water heating system permitting testing operability thereof in situ without draining down the system. The sensor is located in a cavity that has an opening in the bottom thereof in fluid communication with the liquid in the vessel during normal operation of the system. The end of the opening is at a lower elevation than the sensor and liquid from the vessel is in the cavity during normal operation of the system. When the liquid drops to a predetermined low level the sensor activates the safety cut-off. Valved passage means are provided exteriorly of the vessel so that a gas can be injected into the cavity to pressurize the same and drive the liquid in the cavity through the opening into the vessel simulating a low water level condition. At the simulated low water level condition operability of the sensor can be determined. Means are provided to release the gas from the cavity. The sensor is mounted by an insulator that projects into the cavity and the gas release means is spaced from the end of the cavity so that an air pocket is maintained reducing the tendency of conductive deposits to build up on the insulator. A fail safe circuit is provided avoiding malfunctioning of the cut-off safety control should there be a large build up of conductive deposits on the insulator.</p> |
