US2882735A - Safety pilot assembly for burners - Google Patents

Description

R; L.BERGMANN 2,882,735

SAFETY PILOT ASSEMBLYVFOR BURNERS Filed April 27, 1951 April 21 1959 [w r I i l 5 Fl 1 4 I i x I 55 54 5 52 Z v u =nnnnnnnnnr" I l me tutor: R. L. B21; EMANN. 04 21 4 #1 (Ittorneg United States Patent "ice SAFETY PILOT ASSEMBLY FOR BURNERS Richard L. Bergmann, Columbus, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, :1 corporation of Ohio Application April 27, 1951, Serial No. 223,338

3 Claims. (CI. 74-58) The present invention relates to safety pilots for gas burners and more particularly to a safety pilot which shall be well adapted for use with gas-conversion burners for house heating furnaces. In safety pilots of this type it is desirable that the cycling time, or elapsed time after the pilot flame goes out until the safety function operates, be independent of ambient furnace temperatures, that the cycling time be easily adjustable after the safety pilot is installed in a furnace, and that the apparatus be sturdy and reliable in service. The present invention provides a safety pilot which embodies these features.

For a consideration of what I believe to be novel and my invention attention is directed to the following specification and the concluding claims thereof.

In the drawing:

Fig. 1 shows the improved safety pilot applied to a gas conversion burner for a house heating furnace, only a part of the furnace being shown.

Fig. 2 is a side elevation, with parts in section, of apparatus embodying the present invention Fig. 3 is a partial sectional view of a portion of the assembly shown in Fig. 2.

Fig. 4 shows a modification of a detail shown in Fig. 3.

Fig. 5 shows a simplified schematic diagram of an elec trical control system for use with the improved safety pilot.

Fig. 6 is an enlarged view of a portion of the apparatus of Fig. 2.

A gas conversion burner unit for an ordinary househeating furnace 11 is generally indicated at and comprises a casing 12 which extends through the rash-pit doorway of the furnace. The unit also comprises a removable cover 12' over a parts-supporting platform in front of the casing 12. A mixing tube 13 extends through the casing 12 into the furnace chamber for delivering fuel to a burner head 14 positioned in said chamber. A safety pilot 15 is mounted next adjacent the burner head 14 to insure safe operation of the burner. The burner head 14 is shown as of the single-port flame-retention type. Mounted above the burner is a deflector 16 to accelerate combustion and to deflect the burning gases towards the side walls of the furnace chamber, The mixing tube 13 receives gas from means comprising a supply pipe 17 hav ing a control valve 20 (see Fig. 5).

The support for the safety pilot 15 comprises a horizontally disposed frame 21 and an upright bracket 22 mounted on said frame. The safety pilot comprises a thermostat generally indicated at 23, the thermostat comprising an inclined expansion rod 24 having a lateral extension 27, and an upright rod 25, the two rods being welded at their lower ends to a base 26 and welded to each other at their upper ends whereby the assembly forms a triangular structure of three rigid members 24, and 26. An upright heat-shield extends loosely between the two legs or rods 24 and 25 so that heat from a small flame 28 from a pilot burner 33 may selectively heat the expansion rod 24, and by differential expansion Patented Apr. 21, 1959-.

of that rod over the rod 25 causes the top or lapex 23 of the triangular structure to move with respect to the base 26, it being understood that the upright rod 25 is flexed about its lower end by said expansion.

The base 26 constitutes the top of a pedestal 29 which is secured by bolts 31 to 'a shelf 32 forming part of the frame 21. The pilot burner 33 is supported on a shelf 18 on said pedestal 29. A gas-controlling orifice-fitting 34 is threaded into the bottom of the pilot burner 33. A gas-supply tube 35 delivers gas to the orifice fitting 34, and the jet of gas issuing from that orifice draws air Into primary air holes 36 in the side wall of the pilot burner 33. The gas-air mixture so formed issues from ports 37, 38 and 39 adjacent the top of the pilot burner, the top being closed. Where a variety of fuel gases are to be accommodated by the pilot burner, the quantity of air entrained by said jet of gas may be varied by varying the size of the primary air holes 36.

The extension 27 of the expansion nod 24 pushes against the upper end of a lever 40 which is fulcrumed intermediate its end on the upright bracket 22 by a relatively thin and short metal strip 41 having sufficient shear strength to bend like a hinge without offsetting, thus giving rise to no lost motion. A flexing length of 0.0625 inch for a steel strip of 0.025 inch thickness has been found to be suitable, giving a ratio of length to thickness in the hinge strip of five to two or 2 /2/ 1. Softer materials may require a lesser ratio to operate without oft"- setting. The hinge strip 41 is secured to the bracket 22 and to the lever 40 by clamping plates 42 and 43 secured thereto as by rivets 44. To the lower end of the lever 40 there is connected one end of a push rod 46, the rod being threaded into the lever 40 to permit the effective length of the rod to be varied for a reason presently appearing. The rod 46 extends through a square hole in an upturned end 53 of a bracket 52 secured as by screws 54 to a side wall 48 of the frame 21, the rod being slidable in said hole but being square so it may not tum therein. The rod also extends part-way through an axial bore in an elongate switch operating member 50, hereinafter sometimes called a cam member, the rod being slidable in said bore but the bore and rod being square so that the member may not turn on said rod. A cylindrical adjusting rod 47 having a knurled knob at one end is turnable in a hole in an upturned end 45 of the bracket 52. The rod is internally bored and threaded to screw on to the adjacent threaded end 49 of the push nod 46 and is externally threaded to extend into 'a threaded bore in the adjacent end of the elongate member 50. The leads of the internal and external threads on the rod 47 vary a sufficient degree to give a micrometer-type adjustment between the member 50 and the rod 46. Single lead threads of thirty-two and thirty-six threads per inch are suitable for this purpose. In order to prevent the rod 47 from being unscrewed from the rod 46 and from the member 50, the rod may be provided with a fixed collar 56 and the member 50 may be provided with an arm 57 fixedly secured to the latterand having a downturned extension 51 disposed behind the collar to form a stop therefor. Instead of a collar 56 on said rod 47, the body of the latter may have a neck portion as shown in Fig. 4 to provide a shoulder 58 adapted to abut the stop 51 to limit rearward movement of rod 47. A spring 60 between the member 50 and the upturned end 53 of the bracket 52 tends to take up any slack in the connections between the rod 46 and the extension 27 of the thermal element 23.

Mounted on the top side 59 of the frame 21 is a switch mechanism 55 having a spring blade actuating arm 55'. The elongate member 50 is provided with a neck portion 19 wherein the free end of the switch-actuating arm 55' tends to project, the neck portion being provided to form a shoulder 20 which, upon the member 50 being moved towards the right as shown in Fig. 2, will cause the free end of the said arm 55' of the switch 55 to ride up on the shoulder 20 and thus actuate the switch 55.

A spark electrode 77 is secured next adjacent the pilot burner port 37 for initial ignition of the pilot gas. vThe gas from the pilot burner ports 38 and 39 is ignited from port 37 by a runner flame issuing from the small slots connecting the ports 37, 38 and 39. The gas from the port 38 is adapted to ignite the main burner 14, and

the gas from port 39 is adapted to warm the expansion rod 24 of the thermal element 23.

In Fig. a transformer 61 provides 24 volts A.C. to

operate an electrical control system for the burner and the coil 64 to a room thermostat 66 which is in turn con- 1 nected by lead 67 to the transformer 61. A cold contact 70 of the switch 55 is connected by a lead 71 to a spark transformer 72 and thence by lead 73 to a vibrating reed 74 of which only the contact is shown, and which is in turn connected by leads 75 and 67 to the transformer 61. The spark transformer 72 is connected on the high voltage side to ground by lead 76 and to a spark electrode 77 which is adapted to discharge a spark to the pilot riser 33 next adjacent the pilot burner port 37.

In operation, when power is supplied to the 24 v. transformer 61, and the pilot burner is out, the switch 55 is on its cold contact 70, and the contact of the reed 74 is closed. A spark is released at the pilot burner port 37 to ignite gas issuing therefrom. Flame from the pilot burner port 39 warms the expansion leg 24 of the thermal element 23 which thereupon moves towards the left to push on the lever 40. The lever 40 pivots about the hinge 41 and moves the adjusting rod 46 axially to move the switch arm 55 to its hot position, breaking the circuit to the spark electrode and placing the power circuit to the main gas valve under control of the room thermostat 66 as is conventional. In the event that the pilot flame goes out, the thermal element 23 moves to cold position, and the spring 60 forces the adjusting rod assembly and the of expansion such that at a furnace temperature, say, of 400 F., the necessary movement of the apex 23' is but .030 inch, and since the rate: of cooling of the rod 24 is slower in the hot furnace,- this may compensate for the shorter movement required to still give a cycle time of 60 seconds from time of pilot failure to time of opening of the contacts of the switch mechanism 55. It is apparent that, in this example, the apex 23' of the thermal element has moved .010 inch towards closing the contacts of switch 55 upon raising the furnace chamber temperature from 100 F. to 400 F. with the pilot burner oif. In this way constant cycling time, or elapsed time between failure of the pilot and opening of the safety switch 55, is maintained over a wide range of furnace chamber ambient temperatures. The relatively small movement of the apex 23' of the thermal element is accurately adjusted in a floating micrometer assembly by turning a single handle, and unintentional over adjustment is made virtually impossible.

Having disclosed my invention, I claim:

1. An adjusting rod assembly comprising an elongate rod having first and second threaded portions at its respective ends, rod means having internal and external threads having the same direction of advance but different leads, the internal thread being adapted to receive the second thread of said rod, a cam member having an internally threaded portion adapted to receive the external thread of said rod means, and said rod and said cam member being non-turnable with respect to each other i and the rod extending into a bore in said cam member whereby turning said rod means axially moves the cam member and said rod with respect to the other.

2. An adjusting rod assembly according to claim 1 I comprising stop-means for limiting relative axial motion of said cam member and said rod means whereby to prosaid rod may be slidably supported and a second hole lever 40 to follow, thus moving the switch arm 55' to its A nace chamber temperatures the switch is operated at the same relative point. For example, if in a relatively cold furnace at 100 F. having only the pilot burner operating, and the flame 28 playing on the inclined expansion rod 24, upon failure of the pilot burner the apex 23' must move .040 inch to open the contacts of the switch mechanism 7 55, and does so in seconds cooling time, then in a relatively hot furnace the same cooling time is desirable for opening those contacts. This can be obtained by using materials in rods 24 and 25 having dissimilar coeflicients axially aligned with said first hole wherethrough said rod means may be slidably supported, said first hole being non-circular and adapted to support a non-circular portion of said rod whereby to prevent rotation thereof with respect to said bracket, and elastic means acting axially between said cam member and said bracket in a manner tending always to move said cam member axially with respect to said bracket.

References Cited in the file of this patent UNITED STATES PATENTS 1,819,697 Boudette Aug. 18, 1931 2,012,503 Gauger Aug. 27, 1935 2,017,725 Newell Oct. 15, 1935 2,192,629 Beam Mar. 5, 1940 2,192,632 Beam Mar. 5, 1940 2,266,721 Christiansen Dec. 16, 1941 2,291,805 Denison Aug. 4, 1942 2,305,243 English Dec. 15, 1942 2,578,608 Shull Dec. 11, 1951 2,589,804 Harris et al Mar. 18, 1952 2,649,152 Mayer et al. Aug. 18, 1953

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