US3394843A - Lightweight explosion suppressing enclosure - Google Patents

Description

July 30, 1968 C. B. GRADY, JR., ET AL LIGHTWEIGHT EXPLOSION SUPPRESSING ENCLOSURE Filed April 22, 1966 fg a@ i9 Ihr 29 23 29 @i ff ,fd a 1.25

49 IUI-7lIIT-lmwllnllllI-TAlI--WIll-'IIIII-V Lil 'Il'. [IIIA IIA INVENTORS w/e/e United States Patent O 3,394,843 LIGHTWEIGHT EXPLOSION SUPPRESSING ENCLOSURE Charles B. Grady, Jr., 1 Ridgeway Ave., o

NJ. 07052; Miguel G. Mendoza, 48 Park Lane, Fair Haven, NJ. 07701; and Nathaniel B. Wales, Jr., 66

E. 80th St., New York, N.Y. 10021 Filed Apr. 22, 1966, Ser. No. 544,563 6 Claims. (Cl. 220-88) West Orange,

ABSTRACT OF THE DISCLOSURE This invention relates to explosion-proof enclosures for electrical equipment in which it is required that the ignition of a stoichiometric gaseous explosive atmosphere within the enclosure will not ignite a similar explosive stoichiometric gaseous mixture outside and surrounding this enclosure.

The traditional and accepted design to satisfy the foregoing requirement is to build the enclosure with a heavy enough cast metal wall, and with enough closure bolts, and with wide enough machined flanges, so as to be able to withstand without rupture the pressure of the internal explosion, and to cool any escaping gas at the machined parting flange plane to a temperature below the ignition temperature of the surrounding atmosphere. This is, of course, an expensive and cumbersome solution to the problem. However, it is effective and safe.

In the aviation art, this heavy enclosure technique is evidently unacceptable from a weight standpoint, and consequently, where it is considered that an explosive atmosphere is possible, such as from fuel fumes, electrical sparkproducing equipment in aircraft is housed in relatively lightweight enclosures which are not in themselves strong enough to contain the internal explosion, but which are equipped with a Davy screen, that, is, an aperture closed with several ne meshes of fine wire whose purpose is to cool the explosive gases being relieved from the enclosure through this aperture to a temperature below the ignition temperature of the surrounding explosive atmosphere. For such aircraft installations, it is part of a strict program of maintenance to clean or replace these screens at stated intervals.

The reason that this aircraft technique is not considered acceptable for industrial environments is that, over a period of years, and without preventive maintenance, such Davy screens would very probably become clogged with dust, dirt, oil, grease, mud or snow, thereby rendering them ineffective as a relief Vent, and generating a hazardous condition in which an internal explosion would rupture the lightweight enclosure, and ignite the surrounding atmosphere, if explosive.

The present invention overcomes these objections to the Davy screen approach by combining a Davy screen with a dual predetermined pressure relief valve system lwhich permits the heat absorbing Davy screen type material to be chambered in protective isolation from the outside or inside atmospheres and their contaminants until the instant 3,394,843' Patented July 30, 1968 of internal explosion, at which time the valves are blown open at the predetermined pressure differential, thereby saving the mechanical and pneumatic integrity of the enclosures, and cooling the products of combustion to a safe temperature by the uncontaminated porous Davy screen material.

In the preferred embodiments of the invention, these valves immediately reclose after the internal explosion, thereby restoring the system to be ready for a subsequent explosion condition without any further preventive maintenance being required.

Several varieties of relief valve systems suitable for carrying out the teaching of the invention are disclosed.

The principal object of the subject invention is to provide a design of electrical enclosures which is safe and effective, and yet which permits the use of lightweight drawn metal walls.

Another object of the invention is to provide a Davy screen type of explosion inhibitor for electrical enclosure boxes which does not require preventive maintenance to insure the cleanliness and readiness of the screens in spite of dirty environments.

Still another object is to provide a safe explosion-proof enclosure for hazardous industrial environments which can be manufactured for a fraction of the cost of conventional such enclosures.

For other objects, and a clearer understanding of the subject invention, reference is made to the following detailed specifications, to be taken in conjunction with the accompanying drawing, in which:

FIGURE 1 is a cross sectional view in elevation of the preferred embodiment of the invention, showing a lightweight metal electrical equipment enclosure with its sealing flange and its dual system of flap valves to protect its Davy screen;

FIGURE 2 is a cross sectional view in elevation of an alternative form of the invention using resilient ball valves;

FIGURE 3 is a cross sectional view in elevation of a second alternative form of the invention using rubber lip type valves; and

FIGURE 4 is a cross sectional view in elevation of a primitive form of the invention using one-shot valves of rupturable metal foil or membrane.

Referring to FIGURE 1, a typical enclosure for electrical equipment such as relays, circuit breakers, switches, or push buttons (not shown) may be seen to com-prise a lower flanged casing 20 together with an upper flanged casing 21, both of which are secured together at the facing flanges by screws 52.

To improve the sealing between casings 20 and 21, they are provided with resilient rubber or plastic lips 24 and 23 respectively, which extend around the inner peripheries thereof, and are secured thereto by rivets 26 and 25.

It also may ybe seen that any internal pressure within the enclosure formed by casings 20 and 21 will tend to force lips 23 and 24 even more firmly together to enhance this sealing action. The area of contact between casings 20 and 21 will contain a closed line of congruence between these two casings.

The top of casing 21 is provided with a plurality of vent holes 39 or ducts, each of Iwhich is normally sealed by a resilient plastic flap 28 such as of neoprene Flaps 28 are further urged into a sealing relation to apertures 39 by steel leaf springs 29, which, together with flaps 28 are secured to the outside of casing 21 by means of rivets 30, thereby forming an array of flap valves which, in the presence of a predetermined pressure differential between the inside and outside of enclosure 20-21, will open against springs 29, and` relieve this pressure.

Valves 28 vent into an intermediate chamber formed by flanged neck members 33 and 34, and top plate 35 all of which are secured together and to the top periphery of casing 21 by screws.

The top plate 35 is provided with a plurality of vent holes or ducts 40, and, corresponding thereto, a set of valve flaps 36, leaf springs 37, and rivets 38, all identical in design and function to flap valves 28. A metal protective screen 31 is provided and supported within the closed chamber 35, 34, 33, 21 at a level intermediate between top plate 35 and casing 21 to insure freedom of ap valves 28 to open. The edges of screen 31 are impregnated by a plastic sealing compound (not shown) so as to make the joint between members 31, 33, and 34 gas tight. The space between screen 31 and top plate 35 is filled with a metal wool 32 so as to form an elaborated Davy screen capable of rapidly abstracting heat from the products of combustion of an explosion.

The casings and 21 which are preferably made of light weight drawn metal, such as aluminum, are designed so as not to be able in themselves to contain an explosion, but to be strong enough to sustain without damage with a reasonable margin the sum of the explosive pressure differentials across the flap valves 28 and 36, the apertures 39 and 40, and the metal wool 32. It is to be noted that if casings 20 and 21 form a first chamber, necks 33 and 34 form a second chamber which is divided into an intake side (33) and an exhaust side (34-35) by the Davy screen metal wool 32.

It is evident that the enclosure of FIGURE 1 normally seals the metal w-ool 32 away from any contact with any contaminants which may be present either within the enclosure or in the outside atmosphere, due to the sealing action of valves 28 and 36. In the event of an internal explosion the multiple valves 28 and 36 will open, thereby relieving the pressure, and quenching the flame of the explosion gases by the heat abstracting Davy screen action of the metal wool32.

The alternative valve structure shown in FIGURE 2 has the same enclosure casings 20 and 21 and the same sealing lips 23 and 24 as the structure of FIGURE 1.

However, in FIGURE 2 the apertures 39 are closed by hollow resilient rubber balls 42 and the apertures 40 are closed by similar balls 43, which act as relief valves which open at a predetermined differential pressure. Balls 42 are retained by screen 31, while balls 43 are retained by the casing 44 `which is provided with exhaust apertures 45, and which replaces the lid of FIGURE I.

In FIGURE 3, the valving and sealing functions are accomplished by a plurality of opposing resilient rubber or neoprene lips 46 and 48 which are secured to the apertured surfaces 21 and 35, respectively, -by rivets 47 and 50. A guard cap 49 having vents 51 is provided to protect the outer valves 48.

In FIGURE 4 the apertures in the top of casing 21 are closed and sealed by a thin metal foil 53 such as .001 thick aluminum sheet. Similarly, the apertures in top plate 35 are closed by a sheet 54 of metal foil.

Sheets 53 and 54 thus comprise one-shot valve systems which open when a predetermined pressure differential exists across them. Of course, in contradistinction to the devices of FIGURES 1, 2 and 3, the device of 4 FIGURE 4 requires that foils 53 and 54 be replaced after each explosion.

It is to be noted that in all of the foregoing varieties of enclosure, it would be possible to omit the inner valves, 28, 42, 46, or 53 and the neck members 33 and screen 31, if it were determined that there was little probability of contamination of the Davy screen wool 32 from within the enclosure. However, this expedient is not wholly safe, because, if the entire metal wool were permeated by an explosive gas mixture at the time of ignition, there is a good possibility that some of the ignited gas could reach the outside of the enclosure.

Many variations of design will occur to those skilled in the art within the scope of this invention, which is defined in the following claims.

What is claimed is:

1. An equipment enclosure comprising:

a first casing;

a second casing having a closed line of congruence with said first casing and said first and second casings forming together a first chamber;

a second chamber;

a Davy screen dividing said second chamber into an intake side and an exhaust side;

first duct means communicating between said first chamber and the intake side of said second chamber;

second duct means communicating between the exhaust side of said second chamber and the outside atmosphere;

first pressure relief valve means normally closing said second duct means and adapted to open when the pressure on said exhaust side of said Davy screen exceeds the atmospheric pressure by a predetermined differential; and

a second relief valve means normally closing said first duct means and adapted to open when the pressure in said first chamber exceeds the pressure in said intake side by a predetermined differential.

2. In an enclosure according to claim 1:

a first resilient lip within said first cham-ber secured to said first casing around said line of congruence; and

a second resilient lip within said first chamber and secured to said second casing around said line of congruence, and adapted to contact said first lip around its periphery.

3. In an enclosure in accordance with claim 1:

said rst relief valve means being a flap valve.

4. In an enclosure in accordance with claim 1:

said first relief valve being a ball valve.

5. In an enclosure in accordance with claim 1:

said first relief valve being a lip valve.

6. In an enclosure in accordance with claim 1:

said first relief valve means comprising a rupturable membrane.

References Cited 345,681 4/1931 Great Britain.

RAPHAEL H. SCHWARTZ, Primary Examiner.

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