GB1250161A - - Google Patents

Abstract

1,250,161. Controlling burners. GAS COUNCIL. 11 March, 1969 [12 March, 1968], No. 11910/68. Addition to 1,211,199. Heading F4T. A burner control system incorporating the apparatus disclosed in patent Specification 1,211,199 for testing the effective closure of two fuel valves 12, 13 in a supply line 10 to a burner 11, comprises, a cam timer which controls the operation of the valves 11, 13 and the ignition of the fuel, and is operative to test the effective closure of the valves 12, 13 prior to the opening, and after the closing, thereof. The testing means comprises an ejector 17 for applying suction to an enclosure 15 between the valves 12, 13 and a pressure sensor Q for determining the pressure in the enclosure 15 and thus detecting any leakage through the valves 12, 13. The cam timer is driven by a motor SM and has contacts C 1 -C 16 which are closed for the periods shown in Figs. 2 and 2a. The periods are an initial period T 0 , a pre-combustion purge period T 1 , a period T 2 when the flow of air to the burner is reduced to a combustion-level, a pilot burner ignition period T 3 , a pilot burner proving period T 4 , a main burner ignition period T 5 , a main burner proving period T 6 , a main run period T 7 , and a post-combustion purge period T 8 . The periods T 1 and T 8 are subdivided into periods T 11 -T 15 , T 81 -T 85 for testing the closure of the valves 12, 13. The control system is connected to a current supply through live and neutral lines 22, 23. In operation, a switch S is manually closed and, provided that contacts R 2 , J 3 , Z 2 , and K 3 in an interlock circuit 85 (described below) are closed, a relay L/11, having normally open contacts L 2 , L 3 , L 6 , L 8 -L 11 and normally closed contacts L 1 , L 4 , L 5 and L 7 , is energized via the contacts C 10 of the cam timer. Thus, the contacts L 6 close to energize a fan U which passes purging air to the burner, and the contacts L 2 close to start the motor SM. At the end of period T 0 the contacts C 10 open but the relay L/11 is maintained by normally open contacts A of a pressure sensitive switch which is closed by the pressure of the purging air. At T 11 the valves 12, 13 are tested as described in Specification 1,211,199). At the beginning of the period T 3 an electric spark ignition apparatus I is energized through the contacts C 12 , and pilot fuel valves (not shown) are opened by a solenoid P energized through the contacts C 13 . At the period T 4 a solenoid M is energized to open the valves 12, 13, and at the period T 6 the contacts C 2 open to de-energize the motor SM so that the main run T 7 of the burner begins. When the burner is to be shut down, the switch S is opened to deenergize the relay L/11 and thus the solenoid M to close the valves 12, 13. Closure of the contacts L 1 restarts the motor SM to initiate the purge period T 8 by energizing the fan U through the contacts L 7 . During this period the valves 12, 13 are again tested, and at the end of this period the contacts C 1 and C 9 open to de-energize the motor SM and the fan U. The control system incorporates safety controls. If a flame is sensed during the periods T 0 , T 1 , then contacts F 1 of a flame detector F/2 close, a relay J/3 is energized to close contacts J 1 , J 2 and activate an alarm 88. The relay J/3 also opens the contacts J 3 in the interlock circuit 85 to de-energize the relay L/11. If, at any time, the fan U fails then the switch A opens to deenergize the relay L/11, resulting in the closure of the contacts L 1 to cause the motor SM to run through to the start position at T 0 . If, during the valve testing periods, an ineffective closure of the valves 12, 13 is detected, the pressure switch Q close to energize an alarm relay K/3 having contacts K 1 which then close to operate an alarm N. The relay K/3 also has the contacts K 3 in the interlock circuit 85 and these contacts open to de-energize the relay L/11. If, during the periods T 4 -T 7 , flame failure occurs then normally closed contacts F 2 of the flame detector F/2 are closed to energize the relay J/3. The contacts R 2 , Z 2 , in the interlock circuit 85 are the normally closed contacts of reset switches R 1 and Z 1 in the circuits of the relays J/3, K/3 so that a sequence cannot start if these switches are jammed open. Figs. 3, 3a (not shown) describe a modified circuit, these modifications being in the interlock circuit 85 and the circuit of the relay K/3.