GB908660A - Improvements in fuel control means - Google Patents

Abstract

908,660. Controlling burners. RHEOSTATIC CO. Ltd. Dec. 31, 1959 [Jan. 6, 1959; May 15, 1959; Oct. 15, 1959], Nos. 526/59, 16777/59 and 34994/59. Class 75 (1). [Also in Group XL (b)] A device for controlling a burner comprises an electromagnetic relay R adapted to close contacts 9, 10 to energize the heater HM of a thermal delay switch 13 controlling a motor M supplying fuel to the burner and to close contacts 4, 5 to energize the heater HL of a thermal delay lock-out switch 1; and a photo-resistive cell P is disposed in parallel with the relay R so that when the cell is illuminated by the burner flame the relay R is released to de-energize the heater HL of the lock-out switch. In operation when a thermostat TH closes, mains current flows through a current limiting resistance RD, a bridge rectifier BR, contacts 7, 8 of the relay, the heater HL of the lock-out switch and a dropping resistance VR. The relay R is connected across the D.C. terminals of the rectifier and is therefore energized. Contacts 6, 8 therefore close and simultaneously contacts 7, 8 open to substitute an equal resistance RR for the heater HL. The relay contacts 9, 10 energize the heater HM of the motor switch 13 and also the motor M and the heater HL of the lock-out switch 1. A resistance RM reduces the current through the motor and through the heater HL so that neither the motor nor the lock-out switch operate. Further relay contacts 11, 12 energize an ignition transformer T. After twelve seconds the thermal switch 13 operates to open contacts 13, 15 and to close contacts 13, 14. A current sufficient to cause operation is then supplied to the motor M and to the heater HL of the lock-out switch 1 and a current passes through the resistance RM to the heater HM of the thermal switch 13 and is sufficient to hold the thermal switch in operated condition. If the burner ignites the photo-cell P causes the relay R to release whereby the heater HL of the lock-out switch 1 is de-energized at the relay contacts 4, 5. This is the running condition of the burner. In this condition contacts 7, 8 are made so that the heater HL of the lock-out switch is included in the supply circuit of the rectifier but the current is not sufficient to operate the lock-out switch. If ignition fails the relay does not release and the lock-out switch operates after a predetermined time to de-energize the system and energize an alarm A. In a modification the heater for the thermal switch is in two parts and the first part is connected through the relay contacts 9, 10 to the contact 5. If the contacts 4, 5 fail to make the heater HL operates the lock-out switch 1 before the delay switch 13 operates.