US2517478A - Explosion-proof lighting unit - Google Patents

Description

Aug. 1, 1950 M. J. GRIFFIN 2,517,478

EXPLOSION-PROOF LIGHTING UNIT Filed May 1, 1945 a x i7 0 a Zm eW/d/ Patented Aug. 1, 1950 UNITED STATES PATENT OFFICE EXPLOSION -PROOF LIGHTING UNIT Metram J. Griffin, New York, N. Y.

Application May 1, 1945, Serial No. 591,316

4 Claims. 1

The present invention relates to an explosionproof lighting unit adapted to be used in mines, industrial plants, and other places where an explosive atmosphere is likely to be present, and where the use of conventional, exposed lighting units would be dangerous, as constituting a fire hazard, through the possibility of sparks, arcs or overheating of parts thereof. Lighting units of this general type are known in the art, and the present'invention may be considered to be an improvement upon, and modification of, the explosion-proof lighting units shown and claimed in my prior Patent No. 2,304,085.

:As pointed out in the specification of that pat ent, it is important in lights of this type that all parts which might be the source of a spark or heat, or which might otherwise contribute to the initiation of an explosion, or a fire, be enclosed within an hermetically sealed space, in which air or some non-combustible, non-explosive gas is maintained at super-atmospheric pressure, above a predetermined minimum, to the end that the explosive atmosphere surrounding the lighting unit may not gain admission to the inside of the assembly and come in contact with any explosion producing elements. By maintaining the pressureabove the ambient atmospheric pressure, any tendency toward leakage will be outwardly and not inwardly of the casing.

Another vital feature is to provide means for automatically extinguishing the light, in the event that the pressure within the unit falls below a predetermined minimum. Thus, if any of the seals associated with the lighting unit becomes defective, or if the gas or air under pressure therein otherwise escapes, it is important that these facts be indicated, and that the light be extinguished before conditions become dangerous. The bulb circuit must be broken automatically when the pressure in the unit falls below a predetermined minimum, which minimum is still above outside atmospheric pressure.

It isalso important, as pointed out in my prior patent, to make it possible for a, careless workman to re-inflate the unit and thereby re-light the bulb, on the spot, without removing the unit and having the defects therein repaired. In accordance with my prior patent, this practice was preventedby providing a special switch operating mechanism which could not be manipulated to re-close the circuit, without removing the entire lighting unit-from its support. Thus, even though the unit were re-inflated, the switch would not be operated and the unit would have to be removed in any event.

The primary object of the present invention is to prevent the inflation of the unit while it is supported by the electric outlet fixture, so that the automatic switch associated with the unit cannot be closed without removing the unit from the fixture, and removing it to a place of safety, Where the defective part may be repaired. Thus, in accordance with the present invention, it is impossible to inflate the unit in its normal operative position and the danger of introducing an inflammable or explosive gas into the casing is entirely eliminated.

A further object of the present invention is to employ, with complete safety, extremely sensitive, positively acting switches so that the possibility of t e switches failing to open, upon a drop in pressure in the casing, is completely eliminated.

A further object of the invention is to-provide a novel,simple and fool-proof pressure responsive switch operating mechanism.

Other and further objects and advantages of the'invention of the present application 'will be apparent to those skilled in the art from a considerationof the following description of the embodiment shown in the accompanying drawings, in which:

Figure l is a vertical section, with-certain parts shown in elevation, of the li hting unit.

Figure 2 is a side elevation, on an enlarged scale of the switches and switch actuatingmechanism, taken from the right of Figure 1.

Figure 3 is a plan view of Figure 2 and Figure 4 is a circuit diagram.

The electric outlet fixturewith which the light ing unit is associated, and by which it is ,supported may comprise a junction box It), carried by an-electric conduit pipe or other fixed support H, and a terminal socket housing [2 secured to the junction box by a threaded sleeve I3. The lower'fian'ged end M of the housing l2 carries an internally threaded locking ring l5, having a threaded lug l6 associated with its upper flange l7, in'which a set screw it is disposed. The female socket member 58 is secured in the lower open end of the housing by screws 20, and electric wires 2|, 22 extend upwardlyv therefrom through the central hollow bore of the housing and the threaded sleeve l3 into the junction box NJ, where they are connected to the current lines in conventional manner. The joint between the junction box IE! and the housing l2 may be sealed, as indicated at 2'3, and the space above the socket member I!) may be filled with a suitable sealing composition, such as-amixtu're of litharge and glycerol, of substantially the consistency of putty, which sets hard after a short time.

The lighting unit proper comprises an upper switch housing 25, preferably made in two parts, consisting of an upper half 25a and a lower half 25b, secured together by a sectional clamping ring 26, adapted to be drawn tight by screws 2'! threaded in lugs integral with the ring sections. A packing 28,, disposed in substantially semi-circular grooves formed in the upper and lower faces of the end flanges 29, 30 of the housing sections, provides an air-tight joint.

The upper end of the housing section 25a is threaded as at 3|, to receive the internal threads on the locking ring |5 thereby to support the unit as a whole. The open upper end of this member also carries the male plug member 32, held in place by a locking ring 33 and seated upon a gasket 34. The prongs 35 of the plug make contact with the complemental members of the socket l9.

In the lower housing section 25b there is a bracket 31, held in place by a screw 38 and having upturned end members 39, 46, supporting a pair of micro or Mu switches 4|, 42, which are normally open, but which may be snapped to closed position by the application of relatively light mechanical pressure to the buttons .43 associated therewith, as is well understood in the art. 'A Sylphon type bellows 44, supported on the bracket 31 carries a cross arm 45, projecting over a pair of leaf springs 46, 4! mounted on the switch casings and overlying the switch actuating buttons 43. The bellows is so adjusted that, when atmospheric air conditions exist in the housing 25, the cross arm 45 is spaced above the leaf springs 46, and the latter are out of contact with the buttons 43 so that the microswitches are open. As explained below, when the air or gas pressure in the housing 25 is raised above a predetermined minimum, the bellows and the air'within its interior are contracted and compressed, thereby moving the spring fingers 46 into forceful contact with the buttons 43 to close the switches and to maintain them closed, as long as the air or gas pressure is maintained above a predetermined minimum. i

At its lower end, the housing section 251) ter-' minates in a threaded neck 56. receiving a looking ring 5|, adapted to clamp the upper, inturned flange 52 of alight casing 53 in position, between gaskets 54, 55, making an air-tight joint. The neck 56 also carries an internally threaded collar 56, which supports a plate 57 of insulating material carrying a bulb socket 58 and terminal connections 59, 60.

The light casing or reflector 53, made'of spun aluminum or any other suitable material, terminates at its lower end in an angular flange, including an outwardly directed portion BI and a downturned portion 62. The latter is adapted to bite into a U-shaped gasket 63, of rubber, Neoprene or the like, embracing the outer edge of the lens 64 and held in place by an L-shaped metal band 65. A sectional clamping ring 66 has oneflange 6'! underlying the ring 63 and another flange 68 disposed upon an inclined surface engaging the flange 6| of the light casing. As the clamping ring is contracted, by tightening screws 69'threaded in lugs 16, the downturned flange 62 of'the light casing is forcefully-embedded in the gasket 63, thereby providing an hermetic seal. The clamping ring may be made in three, four or more sections.

i The electric light bulb carried by the socket 4 58 is supplied with current by wires 16, 11, one leading to one terminal of one of the microswitches and the other leading to one terminal of the other switch. Wires I8, 19 lead from the other terminals of said switches, respectively, to the two prongs associated with the plug 32, connected in turn through the socket l9 to the current lines. Hence, if either switch opens, the bulb circuit is broken.

The flange 29 of the upper switch housing section a. is apertured at 80 and counterbored and threaded at 8| for the reception of a valve nipple 82, which may be of conventional design and which may contain a standard automobile tire valveassembly. It will be noted that the upper open end of the valve nipple is disposed directly below, and is obstructed by, the flange 83 of the locking ring l5. Hence, when the parts are in assembled position, as shown in Figure 1, access to the inflating nipple is blocked by the locking ring, and it is impossible to place an air hose or inflating chuck thereon to introduce air or gas into the interior of the lighting unit. It will be understood that the interior of the switch housing and of the light casing 53 are in free communicaiton with each other, but that the space within these members is sealed from the outside, by the gaskets 34, 2B, 54, 55 and 63.

In the operation of the lighting unit in accordance with the present invention, after the elements of the unit have been assembled, and before it is attached to the outlet fixture, air or a non-inflammable gas, such as carbon dioxide, under'pressure is introduced through the valve nipple 82. This will cause the bellows 44 to contract, thereby moving the leaf springs 46 into contact with the switch actuating buttons 43 and closing both switches. Hence, the circuit from the prongs 35 through the switches to the bulb 15 will be completed. The unit is installed by first cutting ofI' the line current to the socket til, then inserting the prongs 35 into the socket and screwing the locking ring I 5 upon the threads 3| of the housing section 25a. Set screw |8 is tightened, and the installation is complete. When the line current is turned on, the bulb will be illuminated. In the event of a leak of gas from the interior of the switch housing or light casing, so that the pressurefalls dangerously, the bellows 44 will expand, thereby lifting the cross bar 45 and the leaf springs 46, permitting the switches 4| and 42 to open and extinguish the light. Although it is not essential to employ two switchestheir use is preferred, so that, in the event that one should fail to operate, the other will be certain to function and open the circuit. Moreover, the use of a switch in each line to the bulb is an important safety factor in that it prevents the possibility of a single switch, in one line only, from being by-passed or shunted out of the circuit by contact between that line and the conduit or light fixture above the switch and similar contact between that line and the lighting fixture below the switch. I Such accidental contact between a'line and the metal parts of the conduit or fixture would establish a flow of current around the switch so that, even if the air pressure within the casing fell to atmospheric pressure, and the switch were opened, the circuit would still be maintained and the light would not be extinguished. However, if two switches are used, one in each line, this contingency cannot occur, since one switch will, inevitably, be opened when the pressure falls, thereby extinguishing the light.

It will be impossible for a careless workman to attempt to re-illuminate the light by pumping air or inflammable gas into the interior of the unit, because the valve nipple 82 is blocked by the locking ring [5. Hence, the lighting unit must be removed. It has been found in practice that, if a workman goes to the trouble of removing a defective lighting unit, he will replace it with a properly functioning one, rather than re-inflate and replace the defective one.

The present invention is not limited to the details of construction shown in the accompanying drawings and described above, as many modifications will occur to those skilled in the art, from a consideration of this description. All such modifications as come within the scope of the appended claims and their equivalent are intended to be included.

I claim:

1. In combination, an explosion-proof lighting unit and an-electric outlet fixture having electrical terminal connections and an internally threaded, laterally flanged locking ring associated therewith, said unit comprising casing means defining an hermetically sealed space removably supported by the locking ring, a bulb in said space, electric circuit means leading from the terminal connections to the bulb, switch means in said circuit adapted to be closed by the application of predetermined mechanical pressure and to be opened by the release of said pressure, a bellows in the space movable in response to changes in the gas pressure in the space, an arm carried by the bellows connecting the bellows to the switch, whereby the switch is maintained closed or open, according to the pressure in the space, and a valve nipple projecting upwardly from said casing means for admitting air or gas into the space to raise the pressure therein and thereby to close the switch, the upper end of the nipple being disposed directly below and being obstructed by the flanged locking ring when the latter supports the casing means, whereby the nipple is accessible for introduction of air or gas into the space only when the unit is removed from the outlet fixture.

2. An explosion-proof lighting unit and an electric outlet and unit-supporting flxture having electrical terminal connections and an internally threaded laterally flanged locking ring associated therewith, said unit comprising a casing removably supported by the locking ring and defining an hermetically sealed space, a bulb in said space, electric circuit means leading from the terminal connections to the bulb, switch means in said circuit adapted to be closed by the application of predetermined mechanical pressure and to be opened by the release of said pressure, a bellows in the space movable in response to changes in the gas pressure in the space, an arm for transmitting mechanical pressure from the bellows to the switch, whereby the switch is maintained closed or open, according to the pressure in the space, and a valve con- (luit projecting upwardly from said casing for admitting air or gas into the space to raise the pressure therein and thereby to close the switch, the open end of said conduit being blocked and rendered inaccessible by the flange of the locking ring when the unit is supported by said fixture, whereby the unit must be removed from the fixture before additional gas or air may be introduced thereinto.

3. An explosion-proof lighting unit and an electric outlet and unit-supporting fixture having electrical terminal connections and a laterally flanged, internally threaded locking ring, said unit comprising casing means defining an hermetically sealed space, a light bulb therein, a normally open microswitch in said space in circuit with the bulb adapted to be maintained closed by relatively light mechanical pressure and to be opened automatically by relief of said pressure, a bellows responsive to changes in the gas or air pressure in the space, an actuating arm carried by the bellows for applying and relieving said pressure from the bellows to the switch, whereby the switch is closed when the pressure in the space is above a predetermined minimum and is opened automatically when the pressure falls therebelow, and a valve conduit projecting upwardly from said casing means for admitting therein air or gas to said space to raise the pressure in said space, said conduit being blocked by the flange of said locking ring and being inaccessible when the unit is supported by said fixture, whereby the unit must be removed for purposes of inflation.

4. An explosion-proof lighting unit adapted to be supported by an electric outlet fixture having electrical terminal connections and unit supporting means associated therewith, said unit comprising means defining an hermetically sealed space, a light bulb therein, an electric circuit including two lines leading to said bulb, a pair of normally open micro switches in said space adapted to be closed by relatively light mechanical pressure, each switch being connected in one of the two lines leading to the bulb, a bellows in said space movable in response to changes in the gas or air pressure therein, means for admitting air or gas under pressure into said space and thereby to positively move said bellows, a rigid mechanical connection between the bellows and each switch to transfer mechanical pressure to the switches to close the same, said bellows being positively movable in the opposite direction upon a predetermined drop in the pressure in said space to relieve said mechanical pressure through said connection and to eflect opening of at least one of said switches.

METRAM J GRIFFIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 562,208 Waegel June 16, 1896 583,959 Waegel June 8, 1897 1,294,806 Hunt et a1 Feb. 18, 1919 2,304,085 Griffin Dec. 8, 1942 FOREIGN PATENTS Number Country Date 29,344 Great Britain 1911 525,657 Great Britain Sept. 2, 1940 853,977 France Dec. 23, 1939

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