Apparatus for Heating and Maintaining a Liquid at a substantially Constant Predetermined Temperature until required for use

摘要

1,178,841. Control systems for heating resistors. W. M. STILL & SONS Ltd. 16 Jan., 1966 [17 Jan., 1966], No. 2146/66. Heading H2H. [Also in Division H5] High and low power electric heaters 22, 24 for heating heat-transfer fluid 20 in the jacket 18 of an urn 10, are controlled by a timer 26 which can be set according to the volume of cold liquid added to the bowl 12, and by a thermostat 34, 38 which keeps the contents of the bowl at a predetermined -temperature. When hot liquid is drawn off from the tap 16, a similar quantity of cold liquid is added to the bowl, the calibrated dial 28 of the timer 26 is manually set accordingly, and the double pole on/off switch 54 is switched on. The timer 26 closes the switches 30 and 32 and both high and low power elements are energized. When the temperature of the fluid 20 reaches the desired milk temperature of about 185‹ F., the thermostat 38 will open switch 46, but both heaters 22, 24 will continue to operate until the timer opens switches 30, 32. The timer is calibrated so that it switches off the heaters when the temperature of the heating fluid is considerably above the predetermined temperature but the temperature of the liquid in the bowl will still be below that temperature owing to the time lag in heating. After the timer has switched off, heat flows from the transfer fluid to the liquid until both are at the predetermined temperature. The milk is then kept at this temperature by the thermostat 38 which opens and closes the switch 46 controlling the low-powered element 24. Another thermostat 40 (behind 38) is provided which opens the switch 48 if the fluid 20 becomes overheated.