Patent GB-858149-A (GB)
Title: Improvements in fuel control means
Inventor: KERSHAW PETER LESLIE
IPC: F23N5/20
Filed: 1958-03-19
Abstract: 858,149. Electromagnetic switches; thermal switches. RHEOSTATIC CO. Ltd. Feb. 5, 1959 [March 19, 1958], No. 8819/58. Class 38 (5). [Also in Groups XI and XL (b)] An electromagnetic switch 1, Fig. 1, for controlling a burner comprises two coils evenly divided between two bobbins 1 1b and a pivoted armature 4 operating contacts A, B, C, D, G. One of the coils is energized by pulsating current and a current is induced in the second coil; a half-wave rectifier connected across the second coil ensures that the direction of the induced current is such as to aid the first coil. The armature 4 is pulled in to close contacts A, B, C but contacts G are prevented from closing by a catch 17 secured to the end of a bimetal compensator arm 12 extending from a bimetal coil 13 heated by a heater 14 energized by contacts C. After about 10 seconds the arm 12 moves to disconnect the catch 17 from the contacts G which therefore close to energize a motor supplying fuel to the burner. If the burner ignites a photo-cell is illuminated and energizes the second coil of the switch. After a further 10 seconds the bimetal arm 12 opens contacts D to reduce the pulsating current to the first coil of the switch to a value insufficient, unless aided by the second coil energized by the photo-cell, to hold in the armature 4. If the second coil is not energized by the photo-cell the armature returns to the position shown but the arm 6 connected to the armature carries with it a pivoted latch 7 connected to the arm 6 by a dead-centre spring (not shown) which holds the latch against a stop 9 on the arm. A catch 16 on the latch thus engages the end of the bi-metal arm 12 and therefore prevents the closure of the contacts D. This is a lock-out position and resetting is carried out by moving the latch 7 by hand over its spring centre to abut a fixed stop 10. If, however, the second coil of the switch is energized by the photo-cell the bi-metal arm continues to move and opens contacts E which reduce the current through the heater 14 of the bimetal coil 13 to maintain the bimetal arm in this position, and opens contacts F which deenergize an igniter for the burner. When a demand for heat is satisfied a thermostat deenergizes the first coil of the switch and the armature 4 falls out but the pivoted latch 7 is not carried by the arm 6 but is held instead against the fixed stop 10 by its lower end engaging the end of the bimetal arm 12. The latter therefore returns on cooling to the position of Fig. 1. A thermistor is associated with the first coil of the switch. The switch shown in Fig. 8 comprises two coils arranged as in Fig. 1 and an armature 4 carrying a triple contact strip 59 having contacts A, B, G. A spring 60 tends to open the switch. The contact D is carried on a strip 63 having an inclined end 64 engaging in an aperture 65 in an extension 58 of the armature. A straight bimetal arm 66 is secured by a pivoted angle-bracket 67 to a bimetal compensator arm 68 having an extension 72 which engages below an extension 73 of the strip carrying the contact G. On energization of the switch the contacts A, B close but the contact G is kept open by the compensator arm 68. The heater 14 surrounding the bimetal arm 66 is energized by contacts B and in a short time the compensator arm 68 clears the extension 73 to allow the contacts G to close to energize the motor supplying fuel to the burner. The downward movement of the armature allows the inclined end 64 of the strip 63 to project beyond the aperture 65 so that the strip 63 moves to the right with the compensator arm 68 to maintain the contact D in contact with its contact screw 74. When, however, the strip 63 abuts the aperture 65 the contacts D break to reduce the current to the first coil of the switch. If the photo-cell has sensed a flame the second coil of the switch is energized to hold in the armature and the compensator arm 68 continues to move until it abuts a stud 75 connected by a dead-centre spring 76 to the common contact arm of contacts E, F causing the contacts to be broken to reduce the current in the heater 14 and to de-energize an igniter for the burner. The lock-out mechanisn comprises an L-shaped member 78 pivoted in a groove 79 in the armature 4, one limb being in contact with a fixed stop 80 and the other being connected to a bracket 69 on the armature extension 58 by a dead-centre spring 81. When the armature is pulled in the L-shaped member 78 pivots to bring an aperture 82 in one of its limbs below a finger 83 on the extension 72 of the compensator arm 68. If the second coil of the switch is not energized by the photo-cell the armature falls out when contacts D open, the finger 83 entering the aperture 82. The end of the L-shaped member 78 must be depressed manually to reset the mechanism and release the bi-metal arm. If the second coil of the switch is energized by the photo-cell the compensator arm 68 reaches the terminal position in which the finger 83 comes above the end of the L-shaped member.