Immersion heater

Claim 1

IN AN IMMERSION HEATER FOR HEATING LIQUID HAVING A THERMOWELL WITH ITS UPPER END ABOVE THE DESIRED NORMAL LIQUID LEVEL AND A SECTION AT ITS LOWER END AT AND BELOW THE MINIMUM LIQUID LEVEL, A SHEATHED HEATING ELEMENT HAVING THE GREATER PART OF ITS ACTIVE LENGTH BELOW SAID MINIMUM LIQUID LEVEL AND WITH A PORTION OF THE SHEATH IN ITS ACTIVE LENGTH EXTENDING ABOVE SAID GREATER PART, UP TO SAID MINIMUM LIQUID LEVEL AND UP ALONG ANDUNITED TO THE EXTERIOR OF SAID SECTION OF THE THERMOWELL, A THERMOSTAT MEANS FOR CONTROLLING THE LIQUID TEMPERATURE, SAID THERMOSTAT MEANS HAVING A BULB IN SAID THERMOWELL RESPONDING TO THE TEMPERATURE OF THE LIQUID IN ORDER TO ACTUATE A TEMPERATURECONTROLLING SWITCH, SAID BULB BEING FILLED WITH LOW TEMPERATURE LIQUID WHICH DOES NOT VAPORIZE AT TEMPERATURES IN THE RANGE OF THE LIQUID TEMPERATURES CONTROLLED BY SAID THERMOSTAT MEANS, A CAPILLARY IN SAID THERMOWELL FILLED WITH A LOW TEMPERATURE LIQUID WHICH DOES NOT VAPORIZE AT TEMPERATURES IN THE RANGE OF THE LIQUID TEMPERATURES CONTROLLED BY THE THERMOSTAT MEANS AND IN HEAT TRANSFER RELATION TO SAID SECTION OF THE THERMOWELL WHEREBY UPON DROPPING OF THE LIQUID LEVEL BELOW SAID MINIMUM LIQUID LEVEL THE TEMPERATURE OF THE EXPOSED SHEATH IN THE ACTIVE LENGTH OF THE HEATING ELEMENT RISES AND THE RISE IN TEMPERATURE OF THE EXPOSED SHEATH HEATS THE CAPILLARY AND VAPORIZES LIQUID IN SAID CAPILLARY AND THEREBY GREATLY INCREASES THE PRESSURE WITHIN THE CAPILLARY, A NORMALLY CLOSED SAFETY CUT-OFF SWITCH FOR THE HEATING ELEMENT, AND MEANS RESPONSIVE TO THE INCREASE IN PRESSURE IN THE CAPILLARY DUE TO SAID VAPORIZATION FOR OPENING SAID SWITCH.