US 2675707 A
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April 20, 1954 w. E. BROWN 2,675,707
FUSIBLE RELEASE SAFETY DEVICE FOR FURNACES AND THE LIKE Filed Oct. 2, 1950 2 Sheets-Sheet l p 20, 1954 w. E. BROWN 2,675,707
FUSIBLE RELEASE SAFETY DEVICE FOR FURNACES AND THE LIKE Filed Oct. 2, 1950 2 Sheets-Sheet 2 Patented Apr. 20, 1954 UNITED ENT OFFICE FUSIBLE RELEASE SAFETY DEVICE FOR FURNACES AND THE LIKE William E. Brown, Pewauliee, Wis., assignor to Cutler-Hammer, 1120., Milwaukee, Wis., a corporation of Delaware 3 Claims.
This invention relates to a safety device for furnaces, boilers, space heaters and the like.
It is not infrequent in the operation of furnaces, boilers and space heaters, through malfunctioning of damper systems and fuel supply control, or through neglect of the operator, that such furnaces, boiler and heaters become overheated. Such overheating greatly increases the attendant fire hazard and frequently results in serious damage to the heating system.
A primary object of the present invention is to provide a simple and novel form of safety device which responds to attainment of excessive temperature in furnaces, boilers and space heaters to effect immediate reduction in the rate of combustion therein.
Another object is to provide a safety device of the aforementioned character which may be readily adapted to all kinds of furnaces, boilers or space heaters, and irrespective of the type of fuel or mode of fuel feed utilized in conjunction therewith.
A further object is to provide a device of the aforementioned character that cannot be reset until a condition of safe operating temperatures has been resumed, and
A still further object is to provide a safety device of the aforementioned character which may be readily reset an unlimited number of times without the need for use of tools or replacement of parts.
Other objects and advantage of the invention will hereinafter be apparent.
The accompanying drawings illustrate a pre ferred embodiment of the invention which will now be described, it being understood that the embodiment illustrated is susceptible of various modifications in respect of details without departing from the scope of the appended claims.
In the drawings:
Figure 1 illustrates a warm air furnace together with a damper control system embodying the preferred safety device;
Fig. 2 is an enlarged fragmentary view of a portion of the furnace of Fig. 1 illustrating the safety device in front elevation;
Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2;
Fig. 4 schematically illustrates the use of the safety device in connection with a furnace having motor driven fuel feeding means, and
Fig. 5 schematically illustrates the use of the safety device with a liquid or gas fired space heater.
Referring to Fig. 1, it shows a warm air furnace Hi of the hand fired type wherein combustion is controlled by coordinated operation of a check damper H, located in a smoke pipe 52 connecting the furnace combustion chamber and a chimney l3, and a draft damper i i, located in the ash pit door I5. Dampers II and M are interconnected by a chain or cable It running over guide pulley I! and I8, fixed to the ceiling or overhead support. At one end chain I 5 is connected to damper II and at its other end it is connected to one end of a weight I? which at its other end has connection to damper M. A chain or cable It is connected to the end of Weight ll with which chain It is connected, passes over a pulley 20 and i connected at its other end to the crank arm 2| of a damper regulator motor 22. Pulley 2!! is suspended on one end of a chain or cable 23 which passes over guide pulleys 24 and 25, fixed to the ceiling or overhead support, and which is attached at its other end to the lever arm 26 of safety device 27.
In the position of damper regulator motor 22 and damper control system depicted in Fig. 1, draft damper M will be open to its maximum extent, and it may be assumed that check damper II is closed to its maximum extent. With such positioning of dampers i I and It the combustion rate in furnace Ill will be at, or near, the maximum rate. If the position of crank arm 2| of regulator motor 22 is changed to a position opposite that shown in Fig. 1, then the positions of dampers H and It will be reversed from that aforementioned and the minimum rate of combustion in furnace it will then be afforded.
If the air temperature inside the bonnet 28 of furnace it i maintained below a predetermined safe value, then the position of pulley 20 will be maintained fixed. However, as will be hereinafter more fully explained, if the air temperature inside the bonnet 28 should rise above such predetermined safe value, safety device 21 will function to effect lowering of pulley 20 to such an extent that damper M will automatically close and damper M will be opened to its maximum extent, thereby providing for minimum rate of combustion in furnace lil. Safety device 27 when subjected to temperatures above a predetermined safe value responds to release its arm 26 for movement in the clockwise direction under the bias of pulley 20, weight I? and damper I l. The construction and mounting of safety device 21 in furnace it will now be described in detail.
Referring to Figs. 2 and 3, they show in greater detail safety device 21 and a portion 28 of bonnet 293 immediately adjacent the safety device.
Safety device 21 comprises the aforementioned lever arm 26, a shaft 29, a tube 353, a sprin clutch 3!, a mounting plate 32, and an alloy solder 33.
Mounting plate 32, which is preferably formed of cadmium plated steel or iron, is provided with a central opening to accommodate therewithin with a snug fit the tube 38. Tube 3d, which is preferably formed of brass and annular in cross section, is soldered or brazed to plate 32 for rigid connection thereto. Shaft 29, which is preferably cylindrical in form and made of steel, is adapted to fit within the interior bore of tube 36 with free clearance. Adjacent the end of shaft 29 extending within tube 39, the former is provided with a portion of reduced diameter, and tube 30 is circumferentially crimped, as depicted at 39 so that the inner wall thereof extends almost into engagement with such portion 2%, thereby preventing withdrawal. of shaft 29 axially of tube 36. The end of tube 39 adjacent the aforementioned end of shaft 29 is closed as by bendin the wall of the tube to a meeting relation as depicted at 36 Shaft 29 is normally restrained against rotary movement relative to tube 39 by the solder 33 which in hardened condition efiects a rigid bond between the outer surface of shaft 29 and the inner surface of tube 353. Prior to assembly, the inner surface of tube 3% and the outer surface of shaft 29 are suitably tinned such solder, and after assembly of shaft within tube 36 and the aforementioned crimping and closure of the end of the latter additional solder is introduced between shaft 29 and tube 3d to insure a rigid connection therebetween. The composition of solder 33 will vary according to the permissible maximum furnace air temperature which will differ according to the size and maize of furnace and the design of the heating system. Generally speaking, the desired melting point of solder 33 will be in the range of 250 to 450 Fahrenheit.
Shaft 29 extends outwardly beyond the open end of tube 38am appreciable distance and carries thereon the lever arm 25 and spring clutch 3i. Lever arm 25, which is preferably a one-piece punched and stamped member formed of cadmium plated steel or iron, comprises a flat rectangular portion 25*, triangular side portions ZG -and Et -which merge at a right angle with portion 2% on opposite sides of the latter, and an open-eye hooked portion 25 which merges with one end of portion 26 Portions 28 and 26 of arm 26 are provided with alined openings to accommodate shaft 29.
Spring clutch 3!, which is preferably formed of galvanized music wire, comprises a helical coil portion 3!; an end coil portion Bi and an arm portion 31. The coil turns of the portion 3 I are preferably formed so that when free of shaft 29 the inner diameter of the coil turns will be less than the outer diameter of shaft 29. Shaft 29 is provided with a portion 25 of reduced diameter and the end coil portion 31 of clutch BI is adapted to engage said shaft thereon to restrain the clutch from movement axially of shaft 29. The arm portion 3I of clutch 3! bears against the upper surface of portion 28 of lever 25, extends down through an opening 25 formed in portion 25 and bears against the lower surface of the latter portion. In the assembled relation shown in Figs. 2 and 3, the coil turns of portion 3 i of the clutch tightly grip shaft 29 and the portion 31 bearing against lever 26 restrains the latter against clockwise movement, as viewed in Figs. 1 and 2, on shaft 29.
An opening 34 formed in portion 28 of bonnet 28 is provided to accommodate the tube 30, which tube projects into the chamber inside said bonnet where it is subjected to the air temperature there prevailing. Safety device Z'l is preferably secured in mounted relation on portion 28 of bonnet 28 by stove bolts 35 penetratin receiving openings formed in mounting plate 32 and taking into alined threaded openings formed in portion 2%. Although not shown, a gasket formed of a thermal insulating material such as asbestos may be interposed between mounting plate 32 and portion 28* of bonnet 28 if desired.
The operation of safety device 2? will now be described. Lever arm 26, due to the gravity bias of damper It, weight H and pulley 2b imparted thereto through the chain 23, tends to rotate in the clockwise direction on shaft 25 -iowever, as
' aforeindicated, spring clutch 3! restrains arm 2% against such movement, the restraint increasing with the force applied on-arm If the air temperature within bonnet 28 rises above the melting point of solder 33', the latter softens and when softened sufficiently permits shaft 23 to rotate freely within tube 35. Thus when solder 33 softens sufficiently the assembly comprising shaft 28, spring clutch 3| and lever arm 25 rotates clockwise under the aforementioned bias, assuming a position such as that depicted in broken lines in Fig. 2, thereby affording lowering of pulley 2i; and attendant closing of damper Hi and opening of damper II to reduce the combustion rate in furnace IE] to the minimumrate.
When the air temperature within bonnet 2S thereafter is reduced below the solidifyng point of solder 33, shaft 29 and tube 36 again become rigidly bonded together. Safety device 27 is then in condition for resetting for further safety functioning. Resetting of the device is effected by merely rotating lever arm 25 anticlockwise on shaft 29 to the initial positions therefor shown in Figs. 1 and 2. As will be appreciated, when anticlockwise force is imparted on lever arm 25, the gripping force of the coil turns of portion 3 I of spring clutch 3! will be reduced, thereby permitting anticlockwise movement of arm 2t on shaft 29.
It will be apparent from the foregoing that safety device 2? can be used repeatedly to afford the aforedescribed safety functioning without need for use of tools to reset or replacement of parts following safety action thereof.
While safety device 27 has been shown and described in conjunction with a warm air furnace, it will be apparent to those skilled in the art that the same can be readily adapted to afford the same type of safety action in conjunction with hot water, vapor or steam boilers having the same or similar types of damper and damper control systems. When used with such boilers. the manner of mounting safety device 2? will be different. The most expeditious manner of mounting the same when used with boilers is to provide T fitting in the hot water, vapor or steam line leaving the boiler, providing safety device 2! with a screw thread mounting plug in place of mounting plate 32, and screwing such plug with safety device 21 mounted thereon into an opening of the T fitting. The composition of the solder 33 of safety device 27 will vary according to the heating medium handled by the boiler. For use with hot water boilers the suggested range of melting points for solder 33 is to 208 Fahrenheit. With vapor and steam boilers the desired melting point for solder 33 will depend upon the upper limit of the working pressures of such boilers and should be selected accordingly.
Safety device 21 is also adapted for use with furnaces or boilers where fuel is fed by mechanical devices such as stokers or oil burners. Referring to Fig. 4, it schematically depicts a furnace 40, which may be assumed to be of the warm air type, and a motor driven fuel feeding device 4|, which may be assumed to be a motor driven stoker or oil burner. Device 4| is provided with an electric motor M having electrical supply lines L and L which may be assumed to be connected into any desired type of manual or automatic control system therefor. A switch 42, which here is depicted for the sake of simplicity as a single pole knife switch, is connected in circuit with supply line L Safety device 21 is mounted in the manner aforeindicated in the bonnet of furnace and its lever arm 26 is connected to the handle of the switch 42 by a chain or cable 43 passing over guide pulleys. A weight 44 is attached to the handle of switch 42 and when the arm 26 of safety device 2! is released under safety action of the latter, it effects opening of switch 42 to stop the motor M if the latter is then operating.
Referring to Fig. 5, it shows the use of safety device 21 in conjunction with a space heater 50 which may be assumed to be fed with a gaseous or liquid fuel through pipe 5| having a control valve 52. In this instance the arrangement of safety device 21 is similar to that shown in Fig. 4, and upon safety action of device 21 a weight 53 attached to the handle of valve 52 effects closure of said valve to shut off the supply of fuel to the space heater.
1. A thermally sensitive safety device comprising a tube for subjection to a heat conducting medium, a shaft fitting within said tube and at one end extending outwardly therebeyond, a lever mounted on the outwardly extending portion of said shaft, solder bonding said shaft to the inner wall of said tube for restraining said shaft against rotary movement in said tube whenever the temperature of the latter is below the melting point of said solder, and a spring clutch disposed about said shaft and engaging with said lever to prevent rotation of the latter on said shaft in one direction while allowing unlimited rotation of said lever on said shaft in the opposite direction, said shaft being released to permit rotary movement of the same and said lever in either direction relative to said tube whenever the temperature of said tube exceeds the melting point of said solder.
2. A thermally sensitive safety device comprising a. tube for subjection to a heat conducting medium, a shaft fitting within said tube and at one end extending outwardly therebeyond, solder bonding said shaft to the inner wall of said tube for restraining said shaft against movement relative to said tube whenever the temperature of said tube is below the melting point of said solder, a lever mounted on the outwardly extending portion of said shaft, and a spring clutch disposed about said shaft and engaging said lever for preventing rotation ofthe latter on said shaft in one direction while allowing unlimited rotation of said lever on said shaft in the opposite direction, said shaft being released to permit unlimited rotary movement of the same and said lever in either direction relative to said tube whenever the temperature of said tube exceeds the melting point of said solder.
3. A thermally sensitive safety device comprising a tube formed of a good heat conducting metal for subjection to a heat conducting medium, a shaft formed of metal fitting within said tube and extending at one end therebeyond, said tube and said shaft being complementally formed to insure against withdrawal of said shaft axially of said tube, a lever mounted on the outwardly extending portion of said shaft, solder bonding said shaft to the inner wall of said tube for restraining said shaft against rotary movement in said tube whenever the temperature of the; latter is below the melting point of said solder, and a helical coil spring clutch disposed about and gripping said shaft and engaging said lever for preventing rotation of the latter on said shaft in one 'direction while allowing unlimited rotation of said lever on said shaft in the opposite direction, said shaft being released to permit unlimited rotary movement of the same and said lever relative to said tube in either direction whenever the temperature of said tube exceeds the melting point of said solder.
References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,477,027 Blanchard Dec. 11, 1923 1,688,121 Larson Oct. 16, 1928 1,974,844 Cartwright Sept. 25, 1934 2,150,858 Eggleston Mar. 14, 1939 2,168,749 Olds Aug. 8, 1939 2,190,892 Swepston Feb. 20, 1940 2,302,745 Crise Nov. 24, 1942