Construction of low water level sensing device for hot water boiler

A low water sensing device for use in a pressure hot water heating system to operate a safety cut-off when water in the boiler drops below a predetermined level, said device comprising a housing having an elongate cavity therein open at one end and closed at the opposite end;

• an elongate electrode suspended from an insulator mounted in said housing at said opposite end of the cavity, the axial length of said electrode within said cavity being less than that of the cavity whereby the end of the electrode is offset upwardly from the open lower end of the cavity;
• a first valved air inlet passage means through said housing into said cavity adjacent said opposite end thereof;
• a second air release passage means through said housing spaced a predetermined distance from said opposite end of the cavity in a direction toward said one end;
• and means located between said second air release passage means and said one end of the cavity for sealingly mounting said housing in an opening in the upper wall of the boiler of the pressure hot water heating system with the open end thereof in fluid flow communication with the interior of the boiler.

A method of testing operability of the sensor of a low water cut-off in a pressure hot water heating system having an accumulator therein without draining down the system comprising:

• (a) locating the sensor in a cavity communicating with the interior of the boiler via a passageway extending beyond the sensor, said cavity being at least partially filled with water during operation of the boiler;
• (b) injecting gas from a position exteriorly of the boiler into said cavity to pressurize the same to an extent so as to drive water in the cavity to a level so as to simulate a low water condition and thereby determine whether or not the sensor is operable;
• and
• (c) releasing only a portion of the injected gas from a position spaced downwardly from the upper end of the cavity to thereby maintain a gas bubble of selected size at the uppermost end of the cavity.

In a hot water heating system having water in a boiler and a low water level sensor and safety cut-off device associated with the boiler and operable to shut off the system when the water in the boiler drops below a predetermined level, said low water sensor device comprising:

• (a) a housing having a cavity therein;
• (b) means mounting said housing on an upper wall of the vessel;
• (c) a sensor comprising an elongate electrode suspended from an insulator that projects into the upper end of said cavity and responsive to the liquid level therein, said sensor being operably associated with the heating system to shut off the same when the liquid level in the boiler drops below a predetermined level;
• (d) a passageway in said housing extending downwardly from said sensor into the interior of the vessel and having an open inlet end immersed in the water during normal operation of the boiler, said passageway providing fluid flow communication between the interior of the vessel and said cavity, the inlet to such passage being at a lower vertical elevation than a lower terminal end of the sensor;
• (e) valved passage means in said housing disposed exteriorly of the vessel for injecting a gas into said cavity to pressurize the cavity above the normal pressure therein;
• and
• (f) means, located exteriorly of the vessel, for releasing the gas from said cavity, said gas release means being at a lower elevation than the insulator from which the probe is suspended.