GB2080465A - Liquid-tight end fitting for flexible metallic conduit - Google Patents

Abstract

An end fitting 12 for securing and sealing a length of flexible metallic conduit to an electrical enclosure comprises an externally threaded ferrule 16 which is threaded into the metallic conduit, a sleeve 28 which shrouds the threaded portion of the ferrule 16, an externally threaded tubular nipple 22 for attaching the end fitting 12 to an electrical enclosure and rotatably mounted on the body of the ferrule 16, and an O-ring seal 20 which is located in a recess in the inner end of the nipple 16 and is compressed between the nipple 16 and sleeve 28 to create a liquid-tight seal therebetween. The sleeve 28 serves both as a means for turning the ferrule 16 so as to screw the ferrule 16 into the metallic conduit and to provide a surface against which the outer body of the metallic conduit seals when the ferrule 16 is threaded into the conduit. <IMAGE>

Description

SPECIFICATION Liquid-tight end fitting for flexible metallic conduit This invention relates to an end fitting for sealing and securing a length of flexible metallic conduit to an electrical enclosure.

The use of an end fitting for securing a length of flexible metallic conduit to an enclosure or support is well known. However, no end fitting has been used heretofore, in the form of a one-piece structure, that is capable of being both sealed and secured to the conduit with simple manual twists of the fitting into the conduit. Moreover, no end fitting has been disclosed up to this time that unlocks in a simple manner from mating spiraling grooves in the conduit.

It is an object of the present invention to provide an end fitting that both locks to and unlocks from a conduit in a simple manner.

It is another object of the present invention to provide a simple fluid-tight seal between the end fitting and the conduit.

It is a still further object of the present invention to provide a vibration proof sealed coupling between the conduit and an enclosure.

It is yet another object of the present invention to provide a reusable one-piece fitting between the conduit and an enclosure.

These and other objects are accomplished by an end fitting of this invention that is assembled from four primary parts to form a one-piece fitting unit. All of the parts of the end fitting are centered around a tubular ferrule that has an external screw thread on one end and a outwardly beveled edge on the other end.

A tubular sleeve is press-fit onto the tubular body of the ferrule between the external screw thread and the beveled edge. This tubular sleeve includes a tapered portion that is radially separated from the threaded portion of the ferrule.

The number of threads on the threaded portion of the ferrule is greater, in a given length of the ferrule, than the number of threaded grooves on the interior of the metallic conduit. When the ferrule is screwed in, the greater number of threads causes the grooves in the metallic conduit to compress and force the outer body of the conduit against the tapered portion of the tubular sleeve to form a seal therebetween. Moreover, the ferrule is retained and cannot be unscrewed from the metallic conduit.

An externally threaded nipple is rotatably mounted on the tubular body of the ferrule between the beveled edge of the ferrule and the tubular sleeve. The thread on the nipple is provided for screwing the end fitting and metallic conduit to an electrical enclosure or some other apparatus.

An O-ring seal is located in a recess on the surface of the nipple that is adjacent to the tubular sleeve. The O-ring forces both the tubular sleeve and the nipple outward to provide a liquid seal between them.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which Figure 1 is a part-sectional side elevation of an end fitting in accordance with the present invention; Figure 2a is an exploded fragmentary sectional view of a flexible metallic conduit to which the end fitting is to be attached; and Figure 2b is an exploded fragmentary sectional view showing the flexible metallic conduit and the end fitting attached to each other.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to Figure 1 thereof, a fitting 12 is shown in Figure 1 for sealing and securing a length of plastic covered metallic conduit 14 (shown in Figure 2) to an electrical enclosure (not shown). The fitting maintains liquid tightness and pull-out resistance coupled with reuseability. In addition, with this fitting, a hand-tight attachment to the end of a length of conduit can be made.

The fitting 12 is a machined assembly of four parts attached to one another in such a manner as to provide a one-piece unit rather than a common multiple piece unit. The four basic parts of the fitting 12 are a ferrule 16, a body member 18, an O-ring 20 and an externally threaded nipple 22.

As seen in Figure 1 , the ferrule 16 is a hollow tube-light shaft with an external thread 24at one end. The shaft is machined to have a bore large enough to accept a group of cables contained in the conduit 14.

The external thread 24 is a modified acme screw thread with symmetrical sides inclined at an angle towards a center line through the apex of the thread. The external thread 24 spirals along the shaft with at least two (2) convolutions per inch. This is slightly more convolutions per inch than the spiraling grooves within the conduit 14 when in the relaxed position as shown in Figure 2a.

The body member 18 is a cup-like sleeve, press-fit over the unthreaded portion of the ferrule and is essentially comprised of four sections.

These sections include a pilot/guide section 26, a tapered sleeve 28, a base section 30 and a knurled or nut section 32.

The pilot/guide section 26 is a beveled surface at the outermost but inner edge of the body member 18 and forms a taper at this outermost edge of the body member 18 to allow entry of an end of the conduit 14 into the fitting.

The tapered sleeve 28 is a tapered surface extending from the base 30 of the body member 18 to the pilot/guide section 26. The tapered sleeve 28 is radially spaced from the ferrule 16 and parallels almost the entire length of the external thread 24 to form an annular space. The taper of the sleeve 28 gradually decreases in diameter to a radius at the base 30 that is slightly larger in distance or thickness than the conduit itself when in a relaxed position as in Figure 2a.

The base section 30 of the body member 18 is the inner-most surface of the body member 1 8 that is perpendicular to the outer wall thereof and has a machined bore 34 slightly smaller in size than the outer diameter of the ferrule 1 6.

When the body member 18 is pressed-fit onto the unthreaded portion of the ferrule 16, both the ferrule 16 and the body member 18 behave as a one-piece unit. The knurled or grooved section 32 on the outer portion of the body member 18 serves as a means for hand-tightening the fitting 12 onto the conduit 14. The O-ring 20 is a commercially available rubber-like seal placed over the shank of the ferrule 16 behind the body member 18 to be sandwiched by the externally threaded nipple 22 and the body member 18.

The externally threaded nipple 22 is provided to allow attachment of the fitting 12 to an electrical enclosure (not shown). The opposite end of the externally threaded nipple 22 is fitted with a hexshaped nut 36 to allow the externally threaded nipple 22 to be tightened with a wrench or with pliers to an enclosure. A gasket (not shown) can be located at the flat surface 37 of the externally threaded nipple to ensure a liquid-tight seal between the threads and the enclosure. A recess 38 machined on the top side of the hexed nut 36, at its innermost circumference, provides a recessed area for containment of the O-ring 20.

The inner bore 40 of the externally threaded nipple 22 is slightly larger in size than the outer diameter of the shank of the ferrule 16 to allow free rotation of the externally threaded nipple 22 with the ferrule 16. A bevel or chamfer 42 outward from center is provided on the inner bore of nipple 22, at an end opposite to the hex-shaped nut 36, to allow the ferrule shaft to be flared over the nipple 22, thus holding the nipple 22 to the body member 18 and allowing the nipple 22 to rotate in either direction for attachment to an enclosure.

The flexible-metallic conduit 14, as seen in Figures 2a and 2b is comprised of a plastic cover 44, a metal inner layer 46 and a copper ground wire 48 located between the metal overlapping layer 46. Each spiral of the copper ground wire 48 lies in a concave region 50 formed by inwardly protruding peaks 52 from the plastic cover 44. In Figure 2a the conduit 14 is in a relaxed position, whereas the conduit 14 in Figure 2b is in a compressed state. In Figure 2a, the conduit 14 possesses wide spiraling grooves 54; however, as seen in Figure 2b, the spiraling grooves 54 are compressed.

The result of this assembly is a one-piece coupling which can be attached to the end of a length of conduit 14 by pushing the external threads 24 of the ferrule 16 end first into the conduit 14 and rotating it In a clockwise direction approximately three turns or until manual rotation on the conduit is no longer possible. By doing this, the fitting 12 is locked onto the conduit 14 and a liquid-tight seal is formed between the conduit jacket and the enclosure it is attached to.

The process by which the fitting 12 is locked and sealed to the conduit 14 is as follows. As the fitting 12 is pushed and rotated into the conduit 14, ferrule 16 end first, the end of the ferrule adjacent to and protruding from body member 18 enters the conduit 14 centered by the pilot/guide section 26 of the body member 18. The external thread 24 of the ferrule 1 6 interconnects with the spiraling groove 54 within the conduit 14, as seen in Figure 2b, drawing the conduit into the fitting 12 along the tapered sleeve 28. As the second thread of external thread 24 enters the conduit ;4, two convolutions of spiral will be occupied with thread assuring the compression of the spiraling groove 54 within the conduit.Rotating the fitting 12 still further, compression of the grooves continues until the grooves 54 become closed and the respective grooves cause the jacket of the conduit 14 to be extruded from these grooves pushing the jacket outward at areas 56 against the wall of the tapered sleeve 28 of the body member 18 creating a seal with the jacket. The outwardly pushed areas 56 are located adjacent the protruding peaks 52 of the plastic cover 44. As the spiraling groove 54 is compressed behind the threads 24 of the ferrule 1 6, the diameter of the conduit 14 increases applying added pressure on the jacket. The compressed portion of the conduit 14 within the fitting 12 is no longer flexible. Thus, firm pressure is created on the thread 24 to maintain positive locking of the thread 24 and the grooves 54. In this condition, the grooves 54 are too narrow to allow the thread 24 to back out of the conduit 14.

To release this locking action between the thread 24 and grooves 54, for removal of the fitting 12 from the conduit 14, a sharp blow to the flat of the threaded end of the fitting 12, perpendicular to the ferrule shaft, will spread the grooves 54 occupied by thread 24. This will widen the grooves 54 and allow the thread 24 to be unthreaded from the grooves 54. The diameter of the conduit is reduced and it is returned to its relaxed position. In this relaxed position, the fitting 12 can now be turned in a counter-clockwise direction for removal from the conduit and be ready for later reuse.

Claims (10)

1. An end fitting for sealing and securing a length of flexible metallic conduit to an electrical enclosure comprising; a tubular ferrule which includes an externally screw threaded portion at one end for screwing attachment to grooves on the inner surface of said flexible metallic conduit, said externally screw threaded portion having a greater number of threads in a given length than said internally spiraling grooves In said flexible metallic conduit, and said tubular ferrule including an outwardly flared chamfer at the other end thereof;; -* a tubular sleeve secured to said tubular ferrule adjacent said externally screw threaded portion of said tubular ferrule, said tubular sleeve including a tapered portion radially separated from said tubular ferrule and overlying substantially all of said externally screw threaded portion of said tubular ferrule, and said taperecL#.##po##o#of.##d tubular sleeve being separated from said screw threaded portion of said tubular ferrule by a distance at least as great as the thickness of the wall of said flexible metallic conduit:: an externally threaded tubular nipple rotatably mounted on the other end of said tubular ferrule for attaching said end fitting to said electrical enclosure, said tubular nipple having at one end a bevel that conforms to the chamfer at the other end of said tubular ferrule, and at the other end thereof means for aiding rotation of said tubular nipple when it is being screwed to said electrical enclosure; and resilient sealing means located around the periphery of said tubular ferrule, said sealing means being constrained in a recess provided at said other end of said tubular nipple and arranged to apply pressure to said tubular nipple to force the beveled end thereof against the chamfer at the other end of said tubular ferrule, and to apply pressure to said tubular sleeve to form a liquid tight seal between said tubular sleeve and said tubular nipple.

2. An end fitting as claimed in Claim 1 and arranged such that rotation of the greater number of external threads on said externally screw threaded portion into the lesser number of internally spiraling grooves in said flexible metallic conduit causes the grooves to compress until the grooves are closed thereby pushing the outer surface of said flexible metallic conduit outwardly against said tapered portion of said tubular sleeve and said metallic conduit to form a liquid-tight seal.

3. An end fitting as claimed in Claim 2, wherein said closed grooves prevent said externally screw threaded portion from unscrewing from said internally spiraling grooves.

4. An end fitting as claimed in Claim 3, wherein said externally screw threaded portion is releasable from said closed grooves by a blow to said externally screw threaded portion that is delivered perpendicularly to the axial length of said tubular ferrule.

5. An end fitting as claimed in any preceding Claim, wherein said tapered portion includes a tapered guide section at its outermost edge for guiding said metallic conduit into the space between said tapered portion and said externally screw threaded portion of said tubular ferrule.

6. An end fitting as claimed in any preceding Claim, wherein said tubular sleeve further includes a knurled section on its external periphery for aiding in the manual rotation of said tubular sleeve and said tubular ferrule.

7. An end fitting as claimed in any preceding Claim, wherein said tubular sleeve is secured to said tubular ferrule by a press fit.

8. An end fitting as claimed in any preceding Claim, when arranged to connect and seal a flexible metallic conduit to an electrical enclosure.

9. An end fitting substantially as herein described with reference to the accompanying drawings.

10. The features as herein disclosed, or their equivalents, in any novel selection.