Reusable fitting for corrugated tubing

A fitting for use with corrugated tubing, the fitting comprising: a nut having a passage therethrough for receiving the tubing, the tubing being corrugated tubing having a series of peaks and valleys; a plurality of retainers positioned forward of the nut, the retainers having a sealing surface for placement in a valley of the corrugated tubing; a body having an annular pocket formed circumferentially around the retainers, the body having a body sealing surface, wherein upon sealing, the tubing is compressed between the sealing surface and the body sealing surface; a spring positioned within a cavity in the retainers, the spring driving the retainers into the pocket when the fitting is not sealed.

BACKGROUND

The flexible gas piping (FGP) system, also referred to as corrugated stainless steel tubing (CSST) and formerly Interior Gas Piping (IGP) was developed in Japan and first introduced into that market by Osaka Gas and Tokyo Gas Companies during the early 1980's. The system utilizes stainless steel corrugated tubing supplied in rolls or coils with field attachable fittings to distribute gas from a central supply point such as the meter or regulator to the various appliances within a house or building. The technology, which has likened the process of plumbing a house for gas to wiring a house for electricity, substantially reduces installation time and hence the associated higher cost of labor. The technology was brought to the United States by the Gas Research Institute who saw it as a means of making gas installations more competitive; thereby increasing the percentage of new construction plumbed for gas and increasing the overall consumption of natural gas on a national basis. The technology was enthusiastically endorsed and supported by major gas utilities who had seen the significant higher cost of installed piping as their single greatest obstacle to selling more gas. Code acceptance required more time and effort to obtain, but the product is now recognized by all national model codes and ANSI, the National Fire Protection Association/National Fuel Gas Code and is tested and recognized by the American Gas Association. This product will eventually supplant black-iron pipe which accounts for approximately 80% of all fuel gas piping today, as well as copper tube which, while enjoying many of the same advantages of FGP, is being banned from this application at an increasing rate.

There have been multiple types of fittings put into the field. One fitting introduced into the field used a fiber gasket to make the seal and no special tools were needed to assemble this fitting. This fitting has a higher incidence of leaks than the flared metal to metal seals used by other manufacturers.

Another fitting introduced into the field used first a specialized tool to flatten the convolutions at the end of the CSST tube where the fitting was to be attached and then a second tool was used to put a single flare on the tube end. This product is now off the market due to failures in the tubing caused by work hardening of the stainless steel in the flattening and flaring process.

Another type of fitting was introduced into the field using no special tools to make a metal to metal seal by folding the convolutions of the tube back on itself creating a double flare. After a limited time in the field it was realized that this fitting design was inconsistent in making a leak tight seal. The remedy to the problem was to design an insert type flaring tool; this was used for about three years. A second redesign was conducted, upgrading the insert tool to a socket type flaring tool.

Other fittings have been introduced by the Assignee of the present application and are discussed in U.S. Pat. Nos. 6,276,728, 6,079,749, 5,799,989, the contents of all these patents being incorporated herein by reference in their entirety. While these fittings are well-suited for their intended purposes, improvements may be made in certain aspects of these fittings.

SUMMARY

Embodiments of the invention include a fitting for use with corrugated tubing, the fitting comprising: a nut having a passage therethrough for receiving the tubing, the tubing being corrugated tubing having a series of peaks and valleys; a plurality of retainers positioned forward of the nut, the retainers having a sealing surface for placement in a valley of the corrugated tubing; a body having an annular pocket formed circumferentially around the retainers, the body having a body sealing surface, wherein upon sealing, the tubing is compressed between the sealing surface and the body sealing surface; a spring positioned within a cavity in the retainers, the spring driving the retainers into the pocket when the fitting is not sealed.

DETAILED DESCRIPTION

FIG. 1is a cross-sectional view of a fitting10in an embodiment of the invention. Fitting10includes a nut100, a body200, retainers300and spring400.FIG. 1shows fitting10in an open, partially assembled position. The nut100and body200may be made from metal (e.g., brass) and machined or cast. Tubing500may be corrugated stainless steel tubing (CSST) or other corrugated tubing. InFIG. 1, the fitting is assembled, but not sealed.

Tubing500is shown positioned in the nut100and body200. Tubing500is annular corrugated tubing having an exterior surface having peaks and valleys. Nut100includes a groove102and seal104(e.g., o-ring) at a first, rearward end to seal against a jacket502on tubing500as described in U.S. Pat. No. 6,695,353, the entire contents of which are incorporated herein by reference. The O-ring104resists entrance of foreign material into the fitting.

Nut100includes external threads106that engage internal threads202on body200. As described in further detail herein, nut100includes a nut surface108at a second, forward end on which retainer surface308rides when the body200and nut100are tightened. Similarly, body200includes a body surface204on a second, forward end, on which retainers300ride when the body200and nut100are tightened.

Retainers300include a cavity302positioned at a front face of retainer300for containing spring400. Retainers300include sealing surface304behind cavity302. As described in further detail herein, corrugated tubing is compressed between sealing surface304and body sealing surface206. A retainer rear cavity306at a first, rearward end of retainer300, receives a peak of the tubing500when the fitting is tightened. When disassembled or in a partially assembled state, the spring400drives retainers300into a pocket210formed in body200circumferentially around the retainers300. This moves the retainers300and spring400outside of the outer diameter of tubing500to allow for assembly and disassembly. The tubing500may be freely inserted into or removed from the nut when the retainers300are in pocket210. Thus, the fitting10may be reused.

In the partially assembled state shown inFIG. 1, the body200engages the nut100but threads106and202are not fully engaged. Retainers300are pushed into pocket210by spring400. Tubing500is inserted into the fitting until it contacts body sealing surface206at the second, forward end of body200.

FIG. 2is a cross-sectional view of nut100. As noted above, the nut100includes nut surface108at a second, forward end of the nut100. The nut surface108is angled at an oblique angle less then 90 degrees relative to a longitudinal, central axis of the fitting10. This angle is mirrored on retainer surface308on the first, rearward end of retainer300.

FIG. 3is a perspective view of a retainer300. The fitting includes a plurality of retainers and may have three or more retainers. Spring400is received in cavity302to be positioned outside the outer diameter of the tubing500when the fitting is not sealed. In exemplary embodiments, three retainers are used, each spanning 120 degrees of the tubing. When the fitting is sealed, the three retainers abut at their ends, to form a continuous retainer ring. Sealing surface304compresses one or more convolutions of tubing500against body sealing surface206to form a metal-to-metal seal.

FIG. 4is a cross-sectional view of the body200. Body200includes an annular recess212extending towards a first, rearward end of body200. Recess212receives a forward portion of the retainers300when the fitting is assembled. Body200includes a tapered surface214that serves as a pilot to align the body200with tubing500. The tapered surface214is at an oblique angle with reference to a centerline of the fitting. Tapered surface204is also angled relative to body sealing surface206, which is shown as perpendicular to the centerline of the body200.

FIG. 5depicts spring400. Spring400is a wire spring coiled to a rest state having a diameter greater than the outer diameter of the tubing500. Tabs402on the spring ends are bent inward to prevent spring400from jamming on the surface of retainers300. When the fitting10is unassembled or partially assembled as shown inFIG. 1, spring400forces the retainers outward in a radial direction to position retainers300within pocket210. Retainers300will stay in place in pockets210in the open position even if the fitting is dropped or jarred. As the body200is tightened to the nut100, retainers300move inward in a radial direction compressing spring400. The inward motion of retainers300is driven by angled nut surface108and angled body surface204, both of which form an oblique angle with reference to centerline of the fitting10.

FIG. 6depicts fitting10in a sealed state. As body200is tightened on nut100, the retainers300are driven radially inward through interaction with surfaces108and204as the nut100moves towards body200. This causes the sealing surface304to be placed in a valley behind one or more peaks of corrugated tubing500. As the nut100and body200are further tightened, retainers300enter recess212. As the nut100enters body200, the first convolution of the tubing500is compressed between sealing surface304and body sealing surface206. This forms a metal-to-metal seal between the body200and tubing500and between the retainers300and the tubing500. The seal is such that the outer diameter of the seal is equal to or not substantially greater than the outer diameter of the tubing500. This allows the tubing to be removed from nut100when the nut100and body200are loosened.

Sealing surface304is shaped to closely match the corrugation geometry on tubing500and requires less force to make up. The resulting seal from sealing surface304is not a flare and does not extend beyond tubing outer diameter. Sealing surface304reduces applied stress to the tubing500as compared to conventional flares. Body sealing surface206is a line seal for greater reliability

If the nut100is loosened from the body200, spring400drives the retainers300radially outward until the sealing surface304clears the outer diameter of the tubing500. The tubing500may then be removed. This allows the fitting10to be reused.

A fitting according to exemplary embodiments of the invention provides numerous advantages. The push-on design (i.e., the fitting can be pushed over tubing500) does not require disassembly and is reusable. Fitting10is staked to prevent disassembly and can be made from a wide range of materials.