Abstract:
A coaxial piping system connected between an underground pump and an above-ground liquid dispenser is used to provide containment of the pumped liquid from the underground piping system, preventing unintended release into the environment. A pair of coaxial pipes are removably connected to the underground pump at one end and to the dispenser at the other end using quick-disconnect fittings to allow for the replacement of the piping. A primary pipe for conveying gasoline or the like is surrounded by a secondary pipe, which provides containment in the event of leakage from the primary pipe. The piping system can be tested for leaks or replaced from grade without excavating at the installed tank site. A sensor in the annular space between the primary and secondary pipes may be used to detect leakage. A path may be provided for the gravity drainage of such leaks from the secondary pipe into a containment chamber, where the liquid may be detected and removed.

Description:
This application is a continuation of application Ser. No. 08/778,474 with filing date of Jan. 3, 1997, now U.S. Pat. No. 5,775,842 which is a continuation of application Ser. No. 08/469,652 with filing date of Jun. 6, 1995 (now issued as U.S. Pat. No. 5,590,981), which is a continuation of application Ser. No. 07/286,893 with filing date of Dec. 20, 1988 (now issued as U.S. Pat. No. 5,553,971). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an improved underground piping system for underground tanks used to store hydrocarbon fuels or the like. 
     BACKGROUND OF THE INVENTION 
     Studies by the United States Environmental Protection Agency have found that approximately two-thirds of the leaks in underground storage tanks can be traced to failure of an underground piping system rather than to the tank itself. Specific locations include joints such as unions, elbows and couplings where two straight pieces of pipe are joined together, connections to underground equipment, and corroded steel pipes. 
     Also, structural failure in piping systems can occur when movements take place in tanks and/or piping systems due to high water tables or settling ground movement. This is particularly true in the case of rigid fiberglass piping systems which are subject to cracking or outright structural failure. 
     SUMMARY OF THE INVENTION 
     The present invention provides a piping system for conveying fluid from the outlet port of a pump to the inlet port of a fluid dispenser. The system comprises a primary pipe of flexible material having an inlet end and an outlet end, a secondary pipe of flexible material generally surrounding the primary pipe, a pump coupling removably coupled to the outlet port of the pump, a dispenser coupling removably coupled to the inlet port of the fluid dispenser, and two secondary couplings. A secondary pump coupling removably secures the pump end of the secondary pipe to an outer piping adaptor of the pump coupling. A secondary dispenser coupling removably secures the dispenser end of the secondary pipe to an outer piping adaptor of the dispenser coupling. 
     The pump coupling comprises an inner pipe in communication with the outlet port of the pump and an outer piping adaptor concentric with the inner pipe. The dispenser coupling comprises an inner pipe in communication with the inlet port of the fluid dispenser and an outer piping adaptor concentric with the inner pipe. The inlet end of the primary pipe is removably secured to the inner pipe of the pump coupling, and the outlet end of the primary pipe is removably secured to the inner pipe of the dispenser coupling. 
     The secondary pump coupling comprises a first male-threaded coupling adapted to mate with the outer piping adaptor of the pump coupling and a second portion adapted to mate with the pump end of the secondary pipe. 
     In accordance with the present invention, the annular volume defined by the primary pipe, the secondary pipe, the pump coupling, secondary pump coupling, the dispenser coupling and the secondary dispenser coupling provides containment for the fluid in the event of leakage from the primary pipe. 
     It is an object of the present invention to prevent or decrease the inadvertent leakage of hazardous liquid, such as hydrocarbon fuel, into the environment from an underground storage tank piping system. 
     The present invention provides a double-walled flexible piping system especially suitable for use in conjunction with underground tanks used to store hydrocarbon fuels. 
     An advantage of some embodiments of the present invention is that only two connections are required in the underground piping system. 
     Another advantage of some embodiments of the present invention is that the piping can be replaced without excavating or breaking ground at the installed tank site. 
     An additional advantage of some embodiments of the present invention is that piping is readily accessible from grade for structural testing without excavating or breaking ground at the installed tank site. 
     It is a feature of the present invention that in the event of a leak of the primary pipe, the leak is virtually totally contained within the space between the primary and secondary pipe or in a containment chamber and is not discharged to the surroundings. 
     An additional feature of a preferred embodiment of the present invention is that a sensor placed between the walls of the two concentric pipes provides a method of detecting any release from the primary pipe. For example, a release from the primary pipe may cause an alarm to sound. 
     An additional feature of a preferred embodiment is that any leakage from the primary pipe into the space between the primary and secondary pipes can be drained into a containment chamber, where it can be removed without contaminating the environment. 
     An additional feature of an alternative embodiment is that any leakage into the space between the primary and secondary pipe can be removed by suction at the dispenser connection above ground, so that it can be removed without contaminating the environment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational cross-section of an installed underground fuel storage tank provided with a piping system in accordance with the present invention. 
     FIG. 2 is an elevational cross-section of a portion of the piping system of FIG. 1 showing in greater detail the connection of the flexible pipe with the pump body. 
     FIG. 3 is a cross-section taken along the line 3--3 of FIG. 2. 
     FIG. 4 is an elevational cross-section of another embodiment of a piping system according to the present invention. 
     FIG. 5 is a schematic elevational cross-section of another embodiment of a piping system according to the present invention, including a flexible piping run/manifold connection to other underground storage tank systems. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an underground fuel tank 13 with a single manway 14 at grade level 28, equipped with a containment chamber 12. The containment chamber 12 provides access to a pump 37 and underground piping 19, 22. The underground tank 13 is filled with fuel by opening the manway 14 and transferring fuel to tank 13 through fill pipe 16. 
     A pump 37 is provided to pump fuel from the underground tank 13 through a primary pipe 22 to a fuel dispenser coupling 39 providing input to a fuel dispenser 35. The fuel dispenser 35 may be a conventional service station gas pump. In accordance with the present invention, a secondary pipe 19 jackets the primary pipe 22 and provides containment for any fuel that might leak out of primary pipe 22. 
     To enter the containment chamber 12, one removes the manway cover (not shown), exposing the vapor recovery pipe 11 and the fill pipe 16. The vapor recovery pipe 11 and the fill pipe 16 can then be removed from grade level 28. 
     As shown in FIG. 2, the compression fittings 17, 18 for the secondary pipe 19 and the primary pipe 22 are thereby accessible from the containment chamber 12. The compression fitting 17 for the secondary pipe 19 is disconnected. The male-threaded coupling 20 is next unscrewed from the female-tapped outer piping adaptor 15, and the male-threaded coupling 20 is forced away from the pump 37 and outer piping adaptor 15, thereby exposing the compression fitting 18 connecting the primary pipe 22 with an inner pipe 23 of the piping adaptor 30. The compression fitting 18 can now be disconnected, thus disconnecting the primary pipe 22 and the secondary pipe 19 from the piping adaptor 30 and the pump 37. The other ends of the primary pipe 22 and secondary pipe 19 are similarly disconnected from the dispenser coupling 39 at or about grade level 28. 
     The primary pipe 22 can now be &#34;fished&#34; or pulled up and out from the outer secondary pipe 19 from grade level 28. The primary pipe 22 and the secondary pipe 19 are accessible at both ends--below grade at the interface with the containment chamber 12, and at or about grade level 28 at the fuel dispenser coupling 39. Since the pipes 19, 22 are flexible, the pipe may be shipped to the field site where the tank is installed and cut at the job site to the desired length. 
     The piping adaptor 30 is a forged or cast custom fitting comprising two-inch outside diameter inner pipe 23 connected to an outlet of the pump 37, below ground. The dispenser coupling 39 has a corresponding fitting connected to the dispenser inlet port. The flexible primary pipe 22, having a two-inch inner diameter in this preferred embodiment, fits over the inner pipe 23. The compression fitting 18 clamps and firmly secures the primary pipe 22 to the inner pipe 23. The length of the inner pipe 23 of the piping adaptor 30 is typically two pipe diameters. The compression fitting 18 may be substituted with a common hose clamp, strap or other fitting. 
     The male-threaded coupling 20 is a 4-inch outside diameter steel pipe adaptor with external threads. It screws at its threaded end 55 into the outer piping adaptor 15. In this preferred embodiment, the flexible secondary pipe 19 is 4-inch inside diameter hose piping. It slides over the free end of the coupling 20. A compression fitting 17 clamps and firmly secures the secondary pipe 19 to the male coupling 20. 
     After installation of the flexible piping system, the outside secondary pipe 19 is secured to be relatively stationary as it is buried in the ground. The secondary pipe 19 serves as a guide for the primary pipe 22 which slides into or is retractable from it. 
     The inner pipe 23 has a male thread 25 that screws into the outlet port of the pump 37. (In some cases where the pump has a standard male connection, a standard pipe coupling may be necessary to connect the inner pipe 23.) Once the inner pipe 23 is screwed into the outlet port of the pump 37, the piping adaptor 30 is fixed and is generally not removed. 
     A boot 24 is used to seal the entry of the secondary pipe 19, where it enters the containment chamber 12 by being sealed to a sleeve 21 which is an integral part of the containment chamber 12. 
     If the primary pipe 22 leaks, the leakage is contained in the annular space 27 between the primary pipe 22 and secondary pipe 19, and will not escape into and flood the containment chamber 12. If a leak arises at the juncture of the inner pipe 23 and pump 37, or at either of the two compression fittings 17 or 18, the presence of boot 24 ensures that the leak is contained in the piping containment chamber 12 at interior space 26 and does not overflow into the surrounding soil. The boot 24 also prevents leakage from the fill pipe 16 from escaping from the containment chamber 12 into the soil. 
     The annular space 27 between the coaxial primary pipe 22 and secondary pipe 19 can be tested for leakage in the primary pipe 22 by locating one or more sensors 29 in the annular space 27 between the pipes 22 and 19. 
     Installation Method 
     An installation method will now be described with reference to another preferred embodiment of the invention shown in FIG. 4. 
     First, a flexible secondary pipe 119 is installed below the ground, and then a flexible inner primary pipe 22 is inserted from grade level 128 into the previously installed outer pipe 119. One end of the two concentric pipes 119, 122 is mechanically connected inside the containment chamber 112, which is made accessible by removal of manway cover (not shown). The above-ground ends of the two concentric pipes 119, 122 are mechanically connected inside a containment pan 138 located below a fuel dispenser 135. 
     Accordingly there are only two locations where there are mechanical fittings in the piping run--the connection at the containment chamber 112, and the connection at the containment pan 138. In accordance with the present invention, the only mechanical piping connections at which the primary pipe 122 is likely to leak are located in chambers 112, 138. This must be compared with conventional piping systems wherein many underground connections are employed, and which are buried and inaccessible. To reach these connections it is necessary to excavate much of the piping system in order to find a leak. Furthermore, in the event of a leak at the connection 18 between the primary pipe 122 and the pump 137 in containment chamber 112, manway 114 may be opened and primary pipe 22 may be replaced with a new pipe underground without disturbing the concrete slab (not shown) at grade level 128. So the underground piping is replaceable from grade 128 and without requiring excavation. 
     In FIG. 2, containment of the liquid, in the event of a leak in the primary pipe 22, will be held in the secondary or containment pipe 19, which serves a containment function. FIG. 4 schematically illustrates an alternate embodiment of a piping system between a pump 137 and a dispenser 135 of an underground storage tank--dispenser piping system. In the embodiment of FIG. 4, a leak from the primary pipe 122 will flow into the secondary containment pipe 119, which provides containment of the leak. From the secondary pipe 119, the contained leak will drain by gravity to interior space 126 in the leak containment chamber 112. The coupling 199 securing the primary pipe 122 at the base of the dispenser 135 is connected to the bottom of the shear valve 139. This coupling 199 is substantially similar to the coupling 198 at the other end of the double piping system in the containment chamber 112. The secondary pipe 119 is connected directly to sleeves that protrude from the containment pan 138 at one end and the containment chamber 112 at the other end. The method of connection may be stainless steel straps or bands 157, applied in the field with a strap tightening and clamping tool. Alternatively, a compression fitting may be used. Access to the containment chamber 112 is provided through the manway 114. 
     In either of the embodiments illustrated in FIGS. 2 and 4, monitoring systems are preferably installed where leaks collect so that necessary repairs can be performed without a &#34;release&#34; to the environment. In both the described embodiments, the primary pipe 22 or 122 can be replaced from above grounds. 
     The material of the primary pipe 22 or 122, and the secondary pipe 19 or 119 in the two depicted embodiments is similar to the conventional `hose` construction, i.e. reinforced rubber or plastic material suitable for gasoline service. 
     A gasoline delivery hose--while having a short life-span above ground--will exhibit a substantially longer life when used below ground in darkness (i.e. out of bright sunlight) and in a stationary condition, as illustrated in FIGS. 1, 2 and 4. In such use, there will be no degradation of pipe material due to exposure to sunlight, and no deterioration of pipe material due to wear and tear which accompanies the frequent movement of the pipes which sometimes occurs in above-ground applications. Under such circumstances, the life expectancy of the underground piping system shown in FIGS. 1, 2 and 4 will exceed 10 years instead of the approximately 4 year average life expectancy of conventional above-ground delivery hose applications. 
     Furthermore, in the event of very long runs of pipe between the fuel storage tank and the fuel dispenser, a repeater containment chamber 212 may be placed in the pipe run. The repeater containment chamber 212, primary 222 and secondary 219 pipes, a piping containment chamber 312 and a fuel dispenser 235 are schematically shown in FIG. 5. The use of repeater containment chambers will be necessary in cases where the length of the primary and secondary piping delivered to the jobsite is less than the distance between the piping containment chamber 312 and the fuel dispenser 235, or if multiple fuel storage tanks are utilized and interconnectors in the piping become necessary. 
     It is apparent that the objects of the invention are fulfilled by the foregoing disclosure. It is to be understood, however, that many modifications may be made to the above-described embodiments, some of which have been mentioned above. These and other modifications are to be deemed within the spirit and scope of the above-disclosed invention, which should be interpreted with reference to the following claims.