Abstract:
A riser assembly to transmit gas from a buried fluid line to a manifold. Inner ( 50 ) and outer ( 90 ) casings are received in a first end of an adapter ( 54 ). The other end of the adapter ( 60 ) is secured to the manifold. A gripping assembly ( 70 ) holds the inner casing in the adapter and prevents a pullout while also providing a sealed inner face between the inner casing and the adapter. A mounting assembly is provided to secure the outer casing in the adapter. It, too, prevents pullout of the outer casing and also allows the outer casing to freely rotate relative to the adapter. In selected embodiments the outer casing is formed of a non-corrosive material such as a PVC or polyethelene to address corrosion resistant properties.

Description:
This appln is a 371 of PCT/US98/06438 filed Apr. 1, 1998 and claims benefit of Prov. No. 60/042,301 filed Apr. 1, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     This application is directed to transmission assemblies, and more particularly to gas risers used in transmitting natural gas from a buried underground gas line to a home or business. 
     U.S. Pat. No. 5,590,914 is commonly owned by the assignee of the present application and the details of that patent are incorporated herein by reference. It generally illustrates a gas riser assembly of the type to which the subject invention pertains where natural gas is supplied from a main, through a buried service line, and eventually to the riser assembly. The riser assembly extends from an underground connection with the service line, through an elbow region, to a vertically disposed pipe that communicates with a manifold of an above-ground gas meter. 
     The gas riser assembly is either factory-assembled or intended for assembly in the field. In either case, the gas riser assembly includes a double-walled conduit comprising an inner, plastic tube or casing received inside a rigid, outer casing. The inner casing defines the fluid passage for the gas as it is transported from the main to the meter. Spacers may be provided at selected axial locations along the length of the assembly, if desired. The riser assembly is connected to the manifold in a fluid tight manner so that a sealed passageway is provided from the underground connection to the manifold. 
     Strength of the riser is an important consideration. It must be strong enough to support the weight load of the residential piping system, while maintaining a sealed relationship with the manifold. 
     It is also desirable to use corrosion-free materials in riser assembly since the outer casing, which is typically made of steel, is otherwise subject to corrosive attack. For this reason, the outer casing is usually treated, i.e., coated. The coating operation adds to the overall cost of the assembly. 
     In prior arrangements, the end of the riser that connects with the manifold is a rigid structure. When the riser assembly is connected to the manifold, joint stress can build up in the assembly. Moreover, disassembly required the loss of a gas seal of the tensile grip on the internal tube of the riser assembly. Additionally, the designs were either intended for factory assembly or field assembly, as opposed to being modular in design to allow flexibility. 
     Corrosion resistance is also a concern. It is also preferred that the assembly be electrically isolated from ground contact, and strong enough to support the weight load of the residential piping assembly. Known assemblies, though, often require some type of corrosion protection or an auxiliary support device, i.e., a bracket assembly, to achieve these objectives. 
     Thus, there is a desire for a new and improved riser assembly that achieves these various objectives and results in an extended service life. 
     SUMMARY OF THE INVENTION 
     The present invention provides a riser assembly that overcomes the noted drawbacks in a simple, economical manner. 
     According to the invention, there is provided a riser assembly having an adapter that connects to a manifold at one end, and has an opening at an opposite end adapted to receive the double walled conduits or casings therein. An inner casing is held in the adapter by a gripping assembly. An outer casing concentrically surrounds the inner casing and is held in the adapter by a mounting assembly. The mounting assembly prevents pullout of the outer casing from the adapter and allows the outer casing to freely rotate relative to the adapter. 
     According to another aspect of the invention, the outer casing is a plastic material that provides corrosion resistant and dielectric properties. 
     According to still another aspect of the invention, the outer casing is defined by a metal tube coated in plastic. 
     According to yet another aspect of the invention, the mounting assembly includes a toothed collet. 
     A principal benefit of the present invention is the ability to rotate the outer casing relative to the adapter for ease of assembly and disassembly. 
     Yet another benefit of the present invention resides in the modular design that allows factory or in-field assembly of the gas riser. 
     Yet another advantage of the invention is found in the corrosion resistant, electrically isolated assembly that is able to meet the demands of piping systems. 
     Still other advantages and benefits of the present invention will become more apparent to one skilled in the art upon a reading and understanding of the following specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification. The embodiments are illustrated in the accompanying drawings which form a part of this disclosure. 
     FIG. 1 is a schematic representation of a natural gas distribution system from main to meter. 
     FIG. 2 is a longitudinal cross-sectional view of a first preferred embodiment of the new gas riser assembly. 
     FIG. 3 is an enlarged view of the encircled area of FIG.  2 . 
     FIG. 4 is a longitudinal cross-sectional view of a second preferred embodiment of the new gas riser assembly. 
     FIG. 5 is an enlarged view of the encircled area of FIG.  4 . 
     FIG. 6 is a longitudinal cross-sectional view of a third preferred embodiment of the present invention. 
     FIG. 7 is an enlarged detailed view of the encircled area of FIG.  6 . 
     FIG. 8 is a longitudinal cross-sectional view of a fourth preferred embodiment of the present invention. 
     FIG. 9 is an exploded perspective view of selected components of the gas riser assembly of FIG.  8 . 
     FIG. 10 is an elevational view of the collet used in FIGS. 8 and 9. 
     FIG. 11 is a perspective view of the collet of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, the FIGURES show a main gas supply line A that communicates with a manifold B associated with a residential or commercial establishment via a buried line C and a gas riser assembly D. More particularly, and with reference to FIG. 1, natural gas is supplied from the main A to a first end of the buried service line C. The opposite end of the service line is inserted into a conventional coupling, such as a stab-type coupling  20  which receives a first end  22  of an inner plastic conduit, tube or casing  24 . The first end of the internal tube extends outwardly from a second or outer conduit, tube, or casing  30 . Typically, the outer casing and the inner casing are bent in the form of an elbow at a lower end thereof and the inner and outer casings are maintained in spaced relation by means of annular spacers  32 ,  34 . An upper end  36  of the outer casing is adapted for connection to the manifold B. For example, external threads  38  are provided on the upper end of the outer casing for connection to the manifold. Thus, gas is transported from the main, through the service line, and through the inner casing to the manifold where it is metered before entry into the residential or commercial establishment. 
     The riser assembly is buried in the ground and the outer rigid casing provides suitable protection for the inner casing. Because of the contract with the ground surface, corrosion protection is often provided on the outer casing. For example, the outer casing is often a steel structure that is galvanized with a hot dip zinc or coated with a plastic or epoxy material. 
     Even though prior art assemblies have met with substantial commercial success, it is desirable to use corrosion-free materials to eliminate additional manufacturing steps associated with the coating of the metal casing. On the other hand, strength of the riser is also an important factor. The riser must be capable of supporting the weight load of the residential piping system and still maintain a sealed relationship with the manifold. 
     Turning to FIG. 2, the first or upper end of a first preferred embodiment of the riser assembly is illustrated in greater detail. It includes an inner casing or plastic tube  50  through which natural gas is transmitted from the main to the manifold. A first end  52  of the inner casing is received in an adapter  54 , also known as a service head adapter. As shown, the service head adapter is a generally hollow cylindrical configuration having an opening  56  at a first end that receives the inner tube therein. A second end  58  of the adapter is preferably externally threaded at  60  for mounting the riser assembly to the manifold. 
     A radial shoulder  62  is defined by a first counterbore. The counterbore defines the maximum extent of insertion of the inner tube into the adapter. More particularly, a hollow stiffener  64  received in the end of the inner tube has a radial shoulder  66  that engages the shoulder  62  of the adapter and limits insertion of the stiffener. 
     A gripping assembly is received in the adapter about the inner end of the inner casing  50 . A preferred gripping assembly includes a collet member  70  having an internal toothed profile  72  and an outer tapered surface  74 . A tapered surface cooperates with a wedge member  76  that has a complementary internal tapered surface  78 . Thus, any pullout force imposed on the inner casing  50  is resisted by the cooperating action between the collet and the wedge member which tightly grips the external surface of the inner casing. As will be appreciated, the wedge abuttingly engages a shoulder defined by retaining ring  80 . 
     Inwardly disposed from the collet is a seal assembly defined by a pair of seal members  82 ,  84 . Each seal member is a resilient O-ring that provides a sealed relationship between the external surface of the inner casing and the inner surface of the adapter, particularly along the first counterbore region. Moreover, a ring  86  disposed inwardly of the O-rings serves as both a spacer and also acts to grip the external surface of the inner casing. 
     With continued reference to FIG. 2, and additional reference to FIG. 3, details of the outer casing and its receipt in the adapter are shown therein. Particularly, proceeding axially outward from the retaining ring  80  is a first end of the outer casing  90 . In this embodiment, the outer casing  90  is formed of a non-corrosive material such as a polymer, e.g., polyvinyl chloride (PVC) or a polyethylene. These materials are preferred because they provide both corrosion resistant and dielectric properties. In addition, a reinforcing member such as a thin-walled steel tubing  92  is received along the inner diameter of the outer casing. The reinforcing member preferably includes a radial shoulder  94  that abuts against the terminal end of the outer casing. 
     As illustrated in FIG. 3, the external surface of the outer casing includes a groove that cooperates with a radially extending groove in the adapter to receive a ring  96  that in combination define an outer casing mounting assembly. In this embodiment, the ring has a rectangular profile or cross-section that permits the outer casing to rotate relative to the adapter and prevents pullout of the outer casing. To facilitate make-up of the assembly, a taper region  98  is provided on the inner end of the outer casing. The taper allows the outer casing to be inserted into the adapter opening and past the ring  96 . It cannot, however, be inserted beyond the retaining ring  80  that holds the gripping assembly for the inner casing in place. 
     A second preferred embodiment of the invention is shown in FIGS. 4 and 5 and has many similarities to the embodiment of FIGS. 2 and 3. Particularly, a primary area of distinction resides in the mounting assembly for the outer casing. Here, the retaining ring  196  has a generally circular cross-sectional conformation. Moreover, in this factory-assembled assembly, the retaining ring  80  used in the embodiment of FIGS. 2 and 3 is eliminated and replaced by a radial shoulder  180  that extends inwardly from the adapter. Thus as will be appreciated, the individual components of the gripping assembly that retains the inner casing in the adapter can be assembled in the factory, along with the outer casing and mounting assembly. In this manner, the entire assembled riser is shipped for use in the field and the only required connections are the inner tube to the buried service line and the adapter to the manifold. In substantially all other respects, the embodiment of FIGS. 4 and 5 is similar to that described in association with FIGS. 2 and 3. 
     A third preferred embodiment is illustrated in FIGS. 6 and 7. Where possible, like reference numerals again refer to like elements and new components are identified by new numerals. For example, the inner casing and the gripping assembly associated therewith are substantially unchanged in the third preferred embodiment from that shown and described with reference to FIGS. 2 and 3. However, in this arrangement a reinforcing member  292  in the outer casing  90  does not have a radial flange at the inner terminal end. 
     As may be appreciated, where the outer casing is formed from a hard material such as PVC over steel, it was found that additional tapers were required to allow the outer casing to be inserted into the adapter. Thus, the grooves  294 ,  296  in the inner diameter of the adapter and the external surface of the outer casing, respectively, are modified along with the conformation of the mounting ring to more effectively prevent pullout of the outer casing from the adapter. Particularly, the adapter groove  294  has a tapered conformation  298  along one end then merges into a substantially right-angled or radial shoulder  300  at the other end. Similarly, the mounting ring has first and second tapered portions  302 ,  304 , one of which conforms to the tapered surface in the adapter groove, and the second of which conforms to the tapered region in the external groove of the outer casing. Preferably, these tapers face outwardly from the adapter while the opposite end of the mounting ring has substantially right-angled shoulders  306 ,  308  that limit further insertion of the outer casing into the adapter. The cooperating tapered surfaces assure that additional pullout forces on the outer casing exert a radially inward directed clamping force on the outer casing. 
     In addition, a moisture seal  310  may be provided adjacent the opening in the adapter to prevent moisture from entering between the external surface of the outer casing and the opening in the adapter. 
     FIGS. 8-10 illustrates yet another preferred embodiment of a mounting assembly for the outer casing. In this arrangement, the plastic material of the outer casing is a slightly softer material such as polyethylene. To enhance the resistance to pullout forces, a collet ring  320  is used. It includes a toothed interior surface defined by generally circumferentially continuous, axially spaced teeth  322 . Additionally, an outer surface  324  of the collet member is tapered to cooperate with an elongated tapered region in the groove of the adapter. Thus as pullout forces are exerted on the outer casing, greater radial gripping is transferred by the tapering surfaces that urge the teeth into the external surface of the outer casing. Moreover, the collet is preferably a split arrangement allowing it to be easily slid over the outer diameter of the outer casing. 
     As best illustrated in FIG. 10, one or more barbs  326  extend radially inward from the inner diameter of the collet. These barbs are dimensioned to bite or engage into the external surface of the outer casing. Since there is no requirement that the outer casing be sealed relative to the adapter, it is permissible for the barbs to tightly grip or even scratch the external surface of the outer casing. In fact, it is desirable that the barbs, along with the axial ribs  328  (FIG. 11) assure that the collet member and the outer casing rotate together. That is, if the outer casing is rotated relative to the adapter, the collet member will rotate with the outer casing. In this manner, the outer casing cannot be “unscrewed” relative to the collet because of the presence of the barbs and the axial ribs. Commonly owned international application Serial No. PCT/US98/00630 describes the features and benefits of such an arrangement. 
     As is apparent from the various embodiments, the outer casing can rotate relative to the adapter. This allows the riser to be easily assembled and disassembled in the field from the manifold. Moreover, use of a non-corrosive outer casing addresses concerns with corrosion protection while the insert or reinforcing member still provides additional strength to the outer casing, preferably along the entire length of the riser, or at least to a region below grade. 
     Tool flats  340  can be machined into the adapter or a standard hex-head arrangement can be used to facilitate rotation of the adapter. It is also contemplated that the adapter be coated with an epoxy or other non-corrosive material and the coating would extend over the lower most threads  60  to assure that there is no exposed metal. 
     The present invention is less susceptible to chemical or ultraviolet attack than known arrangements. Moreover, no special tools are required for assembly of the riser in the field. The light weight assembly also reduces installer fatigue. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.