US1973132A - Explosionproof lamp - Google Patents

Description

Sept. 11, 1934. WHEAT 1,973,132

EXPLOS I ONPROOF LAMP INVENTUR ATTIJRNEY,

Sept. 11, 1934. WHEAT I 1,973,132

EXPLOSIONPROOF LAMP Filed Oct. 30, 1931 3 Sheets-Sheet 2 INVENTD ATTORNEY,

Sept. 11, 1934. e. WHEAT EXPLOSIONPROOF LAMP 3 Sheets-Sheet 5 Filed Oct. -30. 1931 E TUR gzlfawf BY I ATTORNEK Patented Sept. 11, 1934 EXPLOSIONPROOF LAMP Grant Wheat, Marlboro, Mass., assignor to Koehler Manufacturing Company, Marlboro, Mass, a corporation of Massachusetts Application October 30, 1931, Serial No. 572,057

12 Claims. (01. 240-1) This invention relates to electric lamps intended foruse in locations where there is danger of creating an explosion due to the presence of dust or highly combustible gases or vapors. Such lamps are desirable, for example, in powder magazines, powder factories, flour mills, celluloid plants, oil refineries, and various other locations.

While lamps of this general type have been developed heretofore for use in mines, these lamps have been restricted to use where very small wattages are required. The chief danger of creating an explosion is due to the breaking of the lamp bulb, thus leaving an exposed highly heated filament open to contact with the surrounding atmosphere. The safety features associated with lamps of this type depend chiefly, if not entirely, upon the interruption of the current going through the lamp filament when the bulb is broken. In those locations where a much greater volume of light is used, as for example in -factories and manufacturing plants of various kinds, an arrangement of the character justdescribed cannot be used for the reason that the filaments of these large lamps retain their heat for an appreciable length of time after the current has been cut ofi from them.

The present invention deals especially with this problem. It aims to devise a lamp structure and lighting system suitable for-use in locations where there is danger of creating an explosion, and in which relatively large lamps can be used safely and without any danger of causing an explosion due to the presence of explosive mixtures in the surrounding atmosphere.

The nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

In the drawings,

Fig. 1 is a vertical sectional view of a lamp structure embodying this invention, and illustrates also certain of the operating connections for the lamp;

Figs. 2 and 3 are diagrammatic views illustrating diflerent systems in which the lamp shown in Fig. 1 may be used; and

Fig. 4 is a vertical sectional view, partly in elevation, of another embodiment of the invention.

Referring first to Fig. 1 the lamp structure there shown comprises a container adapted to hold a body of water and an incandescent electric lamp mounted to burn in a submerged position in said body of water. The container includes a tank 2 and a bowl 3 removably. secured to the .during the burning out of the filament would be lower side of said tank, the bowl being made of glass or other translucent material. The tank may conveniently be given the form of an inverted sheet metal basin. It is provided at its lower edge with a grooved ring 4 adapted to receive the upper thickened edge of the bowl 3. This ring is externally screw threaded to receive an internally threaded and flanged clamping ring 5 which serves to draw the thickened upper margin of the bowl firmly against a packing ring .6 or gasket 6 located in the groove of the ring 4. A watertight joint thus is produced between the tank 2 and the bowl 3. Preferably the ring 5 carries a heavy wire guard 7 which surrounds the bowl.

An incandescent lamp 8 is mounted in an inverted position in the container and includes the usual glass bulb preferably provided with a standard base. This bulb normally is submerged in the water in the container so that if the bulb should be broken the water would immediately rush into ,contact with the filament and cool it. The filament would of course be quickly destroyed by its contact with the water and any are formed promptly quenched by the surrounding water.

For the purpose of supporting the lamp in its operative position a socket member 10 is provided, this'member being made chiefly of sheet metal, and being internally threaded to receive the standard screw threaded lamp base. At its lower end this socket member is provided with a relatively heavy externally threaded ring 12 cooperating with an internally threaded packing sleeve 14 to clamp a packing ring 15 firmly in contact with the neck of the bulb 8. This packing ring may be made of soft rubber or any other material which will prevent the water from working up into the socket.

The socket member also includes a central spring contact 16 to engage the end terminal on the lamp base and this contact is connected with a central terminal 17, the upper end of which is exposed on the top of the socket member. This terminal and its connections are insulated from 100 the metal shell 10 of the socket member.

The socket member is mounted to slide freely up and down in a hollow receptacle 18 which projects through the upper part of the metal tank 2, and is rigidly secured to said tank. Preferably 105 this receptacle is made of some insulating material such as hard rubber, bakelite, glazed porcelain or the like. It carries an internal contact 20 adapted to engage the contact 17 on the socket member 10. Preferably also the contacts 110- 17 and 20 are made of carbon or some other noncorrosive conductive material.

The circuit wires for conducting current to the lamp are contained in a cable 21, one of these wires going to the binding post 22 which is connected directly to the fixed contact 20, while the other is grounded at 23 on the metal cap 24, which encloses the upper part of the tank 2. When the lamp is burning therefore, the current passes through the contacts 20 and 17 to the central terminal of the lamp, thence through the filament to the screw threaded base and into the metal shell 10 of the socket member. From this point it is led through the flexible conductor 25 to the metal frame of the lamp and thence back tothe other supply wire.

It will be observed that with this arrangement the contacts 17 and 20 are held in engagement with each other solely by the buoyancy of the lamp bulb 8. Consequently if the bowl 3 should be broken and allow the water to escape, the lamp bulb would immediately drop, thus opening the supply circuit between the contacts 17 and 20. This action would occur almost instantly and before external inflammable gases could reach the contacts 17 and 20. Furthermore, the tubular form of the lower part of the receptacle 18 and its length are such that a very considerable sliding movement of the socket member inside the receptacle occurs before any substantial communication is provided between the chamber in the receptacle and the surrounding fluids.

During the rising and falling movement of the bulb 8, it is guided not only by the engagement of the socket member 10 with the receptacle 18, but also by a wire guard 26 which closely surrounds the lower part of the bulb 8 and is secured rigidly in a sheet metal ring 2'7. This ring is removably secured to the tank ring 4 by bayonet joints, one of which is shown at 28.

In the construction shown a reflector 30 is provided, this reflector being secured between the ring 4 and the cap 24. It is contemplated that lamps of this type will be suspended from some suitable overhead support, and a chain 31 therefore is secured to the cap 24 of the lamp.

Electric lamps of the incandescent type and especially gas filled lamps of sizable wattages generate considerable heat. There is danger that this heat may become suflicient to melt out the cement in the lamp base, or to build up a steam or vapor pressure in the container 2-3, if this container were closed. In order to obviate this danger provision is made for maintaining a circulation of water through the container. For this purpose inlet and discharge tubes 32 and 33, respectively, are soldered into the tank 2 so' that they may be connected by rubber tubing 34, or in any other suitable manner, in a water circulating system. These tubes pass loosely through holes in the cap 24, the space around the tubes being closed by rubber washers 39.

When an amply supply of water is available several lamps may be connected in series, as shown in Fig. 2, the rate of flow of the water through the system being controlled by a valve 35 of any suitable type and the water discharged from the system simply running to waste. If on the other hand the water supply is relatively limited, then the arrangement shown in Fig. 3

may be used, the water being taken from a parallel instead of in series so far as the water circulation is concerned.

With either arrangement it is desirable to employ some means for automatically cutting off the supply of current to the lamps in the event that the water circulation ceases. This may be accomplished in a variety of ways, one very simple construction being shown in Figs. 2 and 3. It consists simply of a mercury switch 40 mounted on one end of a lever 41 which carries a drip cup 42 on its opposite end. This cup is located immediately under'the end of the discharge pipe 43, the cup forming a reservoir or container which is adapted to hold a suflicient body of water to maintain the lever 41 in approximately the position shown where the mercury switch will be kept closed. This switch is included in the circuit connections running to the entire series of lamps. Consequently so long as water is circulating through the system, the switch will be kept closed and the lamps lighted. A hole is provided in the bottom of the cup 42 through which the water will leak quite rapidly so that if the circulation should stop the cup will be emptied shortly thereafter. The weight of the mercury switch then will overbalance the cup 42 and tip the lever 41 into such a position as to open the switch and cut oil the flow of current to the lamps. The switch preferably is of the usual commercial type including a body of mercury sealed in a closed'glass tube which is filled with an inert gas, two electrodes also being sealed into the tube in suitable positions to be connected or disconnected by the mercury, depending upon the position of the switch.

It will now be evident that the invention provides a lamp structure in which electric lamps of the common commercial types and voltages can be successfully used, while at the same time affording ample protection against explosion. If a lamp bulb should be broken for any reason, the filament will be instantly cooled by the inrush of the surrounding water. On the other hand, if the bowl should be broken soas to allow the water to escape, the lamp circuit would be immediately opened and the lamp put out in the manner above described. The invention. therefore, afiords to the worker an entirely safe source of light adapted to furnish much better illumination than has been given him heretofore.

If the lamp should be struck with sufficient violence to break the chain 31 or any other part of the supporting structure, the dropping of the lamp would be liable to break the cable 21 and thus produce an are which might cause an explosion. In order to avoid this difliculty, I have provided a special connector shown in Fig. 1 which will open automatically under a pull, as for example; that which might be caused by the dropping of the lamp. This connector comprises a shell 44 consisting of two parts 45 and 46, one telescoping within the other. The latter member carries two blade contacts 47-47 which are adapted to slide between split contacts 48 -48 in the other member 45. The latter contacts grip the former with sufficient pressure to hold the two members-of the'connector normally together but permit them to be seperated readily by means of a strong pull. Such a separation breaks the circuit but the telescoping action between the shell members serves to prevent the entrance of combustible gases or vapors into the interior of the shell until after the circuit has been opened ratus includes a container comprising a metal is equipped with tubes or pipes 34' by means of which the lamp may be connected in any suitable circulating system. In the particular arrangement shown the water supply tank into which the upper tube 34' discharges is connected directly to a radiating coil 51 through which the water flows downwardly as it cools oif and finally is conducted back to the tank 2 through the lower tube'34'. The sup ly of water in the tank 50 may be replenished through a combined filling plug and breather or vent valve 52. This lamp operates in the same manner as the construction above described.

While I have herein shown and described preferred embodiments of my invention, it will be understood that the invention may be embodied in other forms without departing from the spirit and scope thereof. It will also be understood that while the circulating liquid has been herein referred to as water, any other suitable liquid may be used.

Having thus described my invention, what I desire to claim as new is:

1. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in said container in position to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part of said bulb surrounded by the water in said container, connections for circulating water from an external source of supply through said container and means controlled by such circulation, for automatically cutting ofl the supply of, current to said lamp if said circulation stops for a substantial length of time.

2. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in said container in position to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part of said bulb surrounded by the water in said container, connections for circulating water from an external source of supply through said container, circuit connections for supplying current to said lamp, said connections including-a switch, and operating means for said switch dependent upon said circulation or water.

3. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in said container in positions to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part 01' said bulb surrounded by the water in said container, connections for circulating water from an external. source of supply through said container, circuit connections for supplying current to said lamp, said connections including a switch, and means for operating said switch automatically in response to predetermined changes in the circulation of water through said container. v

4. In a lamp structure, the combination of a container adapted to hold a body of .water and including a translucent portion, an electric lamp mounted in said container in position to direct its rays through said translucent portion, said'lamp' including a bulb, means forsupporting said lamp with the greater part of said bulb surrounded by the water in said container, connections for circulating water from an external source of supply through said container, a reservoir into which said circulating water is discharged, and means responsive to the supply of water in said reservoir for cutting off the flow of current to said lamp when the supply in said reservoir becomesdee pleted. Y

5. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in said container in position to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part of said bulb surrounded by the water in said container, connections for circulating water from an external source of supply through said container, a drip cup into which the circulating water is discharged, means for supporting said cup for movement in response to changes in the quantity of water held thereby, a

switch arranged to be operated by the movement of said cup, and connections for supplying current through said switch to said lamp.

6. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in said container in position to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part of said bulb surrounded by the water in said container, connections for circulating water from an external source of supply through said container circuit connections for supplying current to said lamp, said connections including an enclosed mercury switch, and

means for operating said switch automatically in response to predetermined changes in said circulation of water.

'7. In a lamp structure, the combination of a container adapted to hold a quantity of water and including a metal tank open at the bottom and a translucent bowl secured to the bottom of said tank, an electric lamp mounted in an inverted position in said bowl and substantially surroundsaid tank, a reflector projecting laterally from the region of the lower edge of said tank, an electric lamp mounted in an inverted position in said bowl and substantially surrounded by the 135. ed by the water in said container, a receptacle water in said container, said lamp including a bulb, a receptacle secured in a fixed position in said tank, a socket member supporting said lamp and slidably mounted in said receptacle, and cooperating contacts on said receptacle and socket member respectively and normally held in connection with each other by the buoyancy of the lamp bulb.

9. A lamp structure according to preceding claim 8 including a guard for said lamp bulb releasably secured to the lower portion of said tank and serving to guide said bulb for vertical movement.

10. A lamp structure according to preceding claim 8 including a cap secured to the lower portion of said tank and enclosing the upper part of the tank.

11. In a lamp structure, the combination of a container adapted to hold a body of water and including a translucent portion, an electric lamp mounted in an inverted position in said container and so located as to direct its rays through said translucent portion, said lamp including a bulb, means for supporting said lamp with the greater part of said bulb surrounded by the water in said container, circuit connections for supplying current to said lamp and including contacts normally held in engagement with each other by the buoyancy of said bulb, and connections for circulating water from an external source of supply through said container.

12. In an apparatus of the character described, the combination of a plurality of lamp structures each including a container adapted to hold a body of water and an electric lamp mounted in said container with the greater part of the lamp bulb surrounded by the water in said container, a circulating system common to all of said lamp structures for circulating water from a source of supply through the containers of all of said lamp structures, circuit connections for supplying current to said electric lamps, said connections including a switch, and means for operating said switch automatically in response to predetermined changes in the circulation of water through said system.

GRANT WHEAT.

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