GB701950A - Improvements in electric temperature and flame-failure control systems for fluid-fuel burning heaters - Google Patents

Abstract

701,950. Automatic temperature control. ROBERTSHAW-FULTON CONTROLS CO. Dec. 28, 1951, No. 30373/51. Class 38 (4). [Also in Group XI] An automatic temperature control system for a fluid fuel burner is also provided with a flame failure control and automatic igniter. The two controls act on two grids of a thyratron in the fuel-valve-solenoid circuit. The circuit is not self-cycling, and locks out on flame failure. The arrangement comprises a main burner 10, and solenoid controlled fuel valve 24, and associated temperature responsive bimetal switch 66 ; pilot burner 18, and associated temperature responsive resister 56, and igniter 22 (controlled through a time-delay circuit 78). A thermal overload cutout 54 is included in the heater transformer primary circuit. To start up the main fuel valve 14 is opened, and the supply switch 16 (linked to the valve) is closed ; igniter 22 lights the pilot burner 18 ; thermal delay switch 94 operates to energize relay 82 which breaks the igniter circuit at contact 86 and at contact 84 de-energizes the thermal delay switch, completes a self-holding circuit and completes the thyratron anode supply. As soon as the pilot burner has heated the temperature sensitive resistor 56 to reduce the bias on the shield grid 36 the thyratron conducts, energizing the solenoid 26 to open the main burner fuel valve 24. At the required ambient temperature thermostat 66 closes its contacts to apply a blocking bias to the control grid 34, thereby de-energizing the fuel valve solenoid. The system then cycles around this temperature. In event of flame failure resistor 56 cools, and the shield grid is biased to cut off thereby shutting off the fuel. The supply switch has to be opened to release relay 82 in the time delay circuit before the igniter can be re-energized. In an alternative arrangement, Fig. 2 (not shown), the thermostat is replaced by a temperature sensitive resistor.