Patent GB-830402-A (GB)
Title: Improvements in electrical control systems for fuel burners
Inventor: HALL COLIN CHARLES
IPC: F23N5/20
Filed: 1955-08-17
Abstract: 830,402. Controlling burners. SUNVIC CONTROLS Ltd., and CLYDE FUEL SYSTEMS Ltd. Aug. 16, 1956 [Aug. 17, 1955], No. 23722/55. 'Class 75(1) [Also in Group XL(b)] In a control system for a burner (not shown) comprising a motor M supplying fuel, means including a transformer IG for igniting the fuel, a thermostat or pressurestat BC for energizing the motor M and the ignition transformer IG to bring the burner into and out of operation, a fluestat FS for example a bimetallic or photocell device responsive to combustion and having contacts H, C in a circuit for terminating the energization of the ignition transformer IG in response to combustion, and allowing energization of the transformer in the absence of combustion, time delay means, master relay means and a holding circuit for the master relay means are provided, the time delay means controlling the motor M and ignition transformer IG in response to the thermostat BC, the master relay means being adapted to remove the time delay means from the circuit in response to the thermostat BC being conditioned to take the burner out of operation, and the holding circuit being controlled by the fluestat FS whereby, in response to the fluestat being conditioned to absence of combustion whilst the thermostat BC is in the condition for bringing the burner into operation, to condition the time delay means to introduce the time delay. The time delay allows purging of unburned fuel from the combustion space. The time delay means comprises a bimetallic relay PR having a heating winding WPR and operating contacts p1, p2. The system includes a manually reset lock-out switch LR which de-energizes the system and energizes a warning light IL if the burner fails to ignite before the expiry of a predetermined time after initial energization of the ignition transformer IG: the lock-out switch LR is operated by a coil WLR. The fuel motor M is controlled by a hot-wire delay vacuum switch WHVS having contacts HVS. The master relay means comprises a first electromagnetic relay MA controlling contacts a1, a2, a3 and a second electromagnetic relay MB controlling contacts b1, b2, b3. At starting the contacts are as shown and only the heating winding WPR of the purge relay PR is energized. After 1“ minutes the purge relay PR opens contacts p1 to de-energize its winding WPR and closes contacts p2 to energize the first electromagnetic relay MA which closes holding contacts a2 and contacts a3 and opens contacts a1. After a further 1“ minutes the purge relay PR has cooled sufficiently to close again contacts p1 and consequently the ignition transformer IG, the operating coil WLR of the lock-out switch LR and the motor switch WHVS are energized. If ignition occurs the fluestat FS breaks contact C and makes contact H to energize the second electromagnetic relay MB which opens contact b1 so that the first electromagnetic relay MA is de-energized and contacts a1, a2, a3 revert to the positions shown. Contact b2 is broken and contact b3 is made to maintain energization of the motor switch WHVS through a ballast resistor R. When the demand for heat is satisfied the thermostat BC opens contact D and closes contact S. The first electromagnetic relay MA is therefore energized and the second electromagnetic relay MB is de-energized. Contacts b1, b2, b3 revert to the positions shown, a1 is opened and a3 is closed but since contact D is open the motor is de-energized. When the thermostat again closes contact D the ignition transformer and the motor switch WHVS are immediately energized without operation of the purge relay PR. In the event of flame failure the fluestat FS opens contact H to de-energize the second electromagnetic relay MB and all the contacts take up the positions shown. The starting operation including the 2¢ minute purge period is then repeated. The circuit may be modified as shown by the dotted lines so that the first electromagnetic relay MA is controlled by the contact C of the fluestat and the heater WPR of the purge relay is controlled by the contact b1 of the second electromagnetic relay MB. In this arrangement the contact a3 opens when the fluestat breaks contact C and unless the fluestat makes contact H within the two seconds delay of the motor switch WHVS the motor will be de-energized. In a modified embodiment the fuel oil is heated by a heater controlled by a thermostat responsive to the oil temperature and adapted to operate contacts connecting the motor switch WHVS and the ignition transformer IG to the electric supply in such manner that energization of the switch and transformer is only possible when the oil is at a predetermined temperature. An alternative means of connecting the motor switch WHVS and the ignition transformer IG to the electric supply is provided by contacts closed by energization of the second electromagnetic relay MB. The motor is a three phase one and has a three phase contactor having its operating coil connected in circuit with the contacts HVS of the motor switch WHVS. The three phase contactor may include an overload trip adapted to open contacts in series with the contactor operating coil. A thermostat de-energizes all the circuits if the temperature of the oil fuel rises above a predetermined safe value. Specification 778,205 is referred to.