Abstract:
An expansion joint for a fluid piping system is described. The expansion joint is formed of a corrugated cylindrical bellows constrained by a linear sheath within which the expansion joint can contract as the ends of adjacent pipes move closer together due to heat expansion.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to fluid piping systems. More particularly, this invention pertains to expansion joints for relieving heat expansion stress in a fluid piping system. 
     It will be appreciated by those of skill in the art that fluid piping systems designed to transport fluids in settings such as dialysis clinics, research laboratories, certain manufacturing facilities and food processing plants must be periodically disinfected. 
     The prior art fluid piping systems, with multiple solvent-welded joints and cavities which are relatively inaccessible for disinfection provide a suitable environment for growth of a number of pathogenic microorganisms, such as Pseudomonas species. The inventors have described, in U.S. patent application Ser. No. 09/206,904, for a “System for Fluid Delivery in a Dialysis Clinic,” filed Dec. 7, 1998, the details of which are incorporated herein by reference, a novel fluid piping system which minimizes the recessed surfaces where bacteria may freely grow. However, since Pseudomonas, particularly, can grow along internal surfaces of a tube filled with sterile water, periodic disinfection of the piping system is required. 
     Currently, disinfection of fluid piping systems in health care clinics, particularly dialysis clinics, utilizes a combination of chemical and high temperature disinfection means. The high temperatures required for heat disinfection of conventional systems place considerable expansion stress on the piping systems. Chemical disinfectants are therefore used to allow heat disinfection temperatures to be decreased. 
     Chemical disinfectants, however, provide an added risk to patients in a dialysis clinic. Formaldehyde, for example, may cross dialysis membranes to enter the patient&#39;s bloodstream and stimulate antibodies to the patient&#39;s own DNA. Therefore, a more acceptable disinfection program would provide disinfection using heat alone. 
     What is needed, then, is a component for a fluid piping system that would facilitate heat disinfection by reducing expansion stress within a fluid piping system exposed to high temperatures for prolonged periods of time and capable of repeated cycling without compromising the integrity of the expansion compensating component. 
     SUMMARY OF THE INVENTION 
     An expansion joint is provided for connecting pipes in a fluid piping system. The expansion joint is particularly designed to reduce heat expansion stress in a fluid piping system. 
     The expansion joint includes a cylindrical bellows connected between pipes in the fluid piping system. Also included is a sheath enclosing the cylindrical bellows. During heat disinfection, distortion of the cylindrical bellows is limited by the sheath, while the lack of fixed attachment of the sheath allows the couplings connecting the expansion joint to the adjacent pipes in the fluid piping system to freely slide towards each other as the pipes expand due to heat expansion. 
     The cylindrical bellows is preferably formed of corrugated polymer tubing. In a preferred embodiment of the invention, the bellows is formed of a corrugated polytetrafluoroethylene tube that is stable at a temperature of 105 degrees Celsius applied for a period of at least 20 hours. 
     Couplings at the ends of the corrugated bellows provide connectors for attachment to complementary couplings at the ends of adjacent pipes in the fluid piping system. 
     In a preferred embodiment, the couplings allow replacement of the expansion joint, most preferably by providing threaded connections that can be easily installed and removed. 
     Installation of the removable sheath is accomplished by fitting the sheath over the length of the corrugated bellows and adjacent couplings, facilitated by a lengthwise split in the sheath. The sheath is preferably formed of polymer tubing. 
     An object of the present invention is to provide a means to reduce heat expansion stress in a fluid piping system. Another object of the invention is to provide a component of a fluid piping system which facilitates the use of high temperatures for prolonged periods of time during heat disinfection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the expansion joint of the present invention. 
     FIG. 2 illustrates the method of connection of the removable coupling members of the coupling of the present invention. 
     FIG. 3 is an enlarged view of the assembled expansion joint. 
     FIG. 4 illustrates the completed installation of the expansion joint of the present invention in a fluid piping system, such as that described by U.S. patent application Ser. No. 09/206,904, for a “System for Fluid Delivery in a Dialysis Clinic,” filed Dec. 7, 1998. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a component of a fluid piping system that reduces heat expansion stress in a fluid piping system and thereby facilitates heat disinfection and eliminates the need for chemical disinfectants during the heat disinfection process. 
     To overcome the shortcomings in the prior art for a piping system which can be heat disinfected for transporting fluid in the health care facility, the inventors have created an expansion joint  10 , the assembly of which is illustrated in FIG. 1, for connecting first  18  and second  20  lengths of piping in the system. As shown in FIG. 1, the expansion joint comprises a cylindrical bellows  12  with first  14  and second  16  couplings connecting the bellows  12  to the first  18  and second  20  lengths of piping respectively. The first coupling  14  is formed of a cylindrical pipe coupling member  22  fused to the first pipe  18  and a cylindrical bellows coupling member  26  fused to the bellows  12 . 
     A further component of the expansion joint  10  is a sheath  32  received about the bellows  12  and slidably engaging each of the first  14  and second  16  couplings so that when the pipes  18  and  20  expand longitudinally and the bellows  12  compresses, the sheath  32  will slide over at least one of the first  14  and second  16  couplings. 
     In a preferred embodiment, the sheath  32  is a lengthwise rigid continuous member extending from the first coupling  14  to the second coupling  16 . The sheath  32  further comprises a cylindrical member having a lengthwise split  34  defined therein so that the sheath is radially flexible, allowing it to flexibly grip the first  14  and second  16  couplings. Furthermore, in the expansion joint  10  described herein, the sheath  32  preferably has a length greater than five times its diameter. The radial flexibility provided by the lengthwise split  34  allows the sheath to be placed over and around the cylindrical bellows  12  so that the sheath flexibly grips the first  14  and second  16  couplings. 
     In a preferred embodiment of the invention, the bellows  12 , the couplings  14  and  16 , and the sheath  32  are all constructed of plastic material. The bellows  12 , the couplings  14  and  16 , and the sheath  32  are most preferably constructed of a heat-resistant hydrocarbon polymer, the cylindrical bellows being formed of a length of corrugated tubing. In a particular preferred embodiment, the cylindrical bellows is composed of the heat resistant polymer polytetrafluoroethylene (PTFE), also known by the commercial name Teflon® (Dupont). 
     As shown in FIG. 2, first pipe coupling member  22  and first bellows coupling member  26  can be connected in a detachable manner by forming the first pipe coupling member  22  as a female-threaded fitting and forming the first bellows coupling member  26  as a male-threaded fitting, so that the connection can be made when the male-threaded bellows coupling member  26  is threadably received into the female-threaded pipe coupling member  22 . In a preferred embodiment of the invention, the first pipe coupling member  22  has an outside diameter greater than an outside diameter of the first bellows coupling member  26 . In an alternate embodiment of the invention, couplings  14  and  16  can be formed of quick-connect fittings, such as those described and illustrated in U.S. patent application Ser. No. 09/206,904. 
     As illustrated in FIG. 3, the present invention provides an expansion coupling  10  connecting an end of a first pipe  18  in a fluid piping system and an end of a second pipe  20  in a fluid piping system. A cylindrical bellows  12  having a first end  38  and a second end  40 , is fluidly connected to first pipe  18  and second pipe  20 . The fluid connection is achieved by connecting a first bellows coupling member  26 , attached to the first end  38  of the cylindrical bellows  12 , to a first pipe coupling member  22 , attached to the end of the first pipe  18 , and connecting a second bellows coupling member  28 , attached to the second end of the cylindrical bellows  12 , to a second pipe coupling member  24 , attached to the end of the second pipe  20 . Attachment of bellows coupling members  26   28  to bellows ends  38   40 , respectively, and attachment of pipe coupling members  22  and  24  to the ends of pipes  18  and  20 , respectively, can be accomplished by fusing the coupling members to the corresponding ends of the pipe or bellows. The first end of a sheath  32  is received over the first pipe coupling member  22  and a second end of the sheath  32  is received over the second pipe coupling member  24  by means of a lengthwise split  34  in the sheath which gives the sheath radial flexibility. In the expansion joint  10  and expansion coupling  10  of the present invention, the cylindrical bellows  12  is formed of corrugated tubing which is stable at a temperature of 105 degrees Celsius applied for a period of at least twenty hours, the time and temperature requirement being mandated by acceptable standard disinfection conditions for fluid piping systems in a health-care facility. 
     It will be appreciated by those of skill in the art that fluid piping systems used to transport purified fluids must be periodically disinfected to reduce bacterial contamination. Standard disinfection methods requiring only the application of heat are preferable to those disinfection methods that require a combination of heat and chemicals, since the use of chemical disinfectants poses associated risks. Standard heat disinfection methods, however, require the use of high temperatures for prolonged periods and repeated heat disinfection cycles. Exposure to high temperatures for the prolonged periods of time necessary for heat disinfection places considerable heat stress on the piping system and repeated cycling may result in low cycle stress fatigue failure. Therefore, in the method of the present invention, thermal expansion stress in a fluid piping system is reduced during application of heat sufficient to produce temperatures above 100 degrees Celsius for prolonged periods of time. Reduction of thermal expansion stress as described by this method is accomplished by connecting a first pipe  18  and a second pipe  20  to the piping system. To the first pipe  18  is connected a first end of a cylindrical bellows  38  and to second pipe  20  of the piping system is connected a second end of the cylindrical bellows  40  by means previously described. The fluid within the system is heated to a temperature of at least 105 degrees Celsius for a period of at least twenty hours in order to accomplish heat disinfection of the system as prescribed by industry standards. Heating fluid within the system to the required temperature produces longitudinal expansion of the first pipe  18  and the second pipe  20 . Longitudinal expansion of the first  18  and second  20  pipes respectively, results in compression of the cylindrical bellows  12  along its length. Since heat expansion may cause longitudinal expansion of the cylindrical bellows  12  itself with resulting deformation, the cylindrical bellows  12  is housed within a sheath  32  to reduce the deformation of the bellows as heat is applied to the system. 
     The present invention also describes a method of using heat disinfection, without application of chemical disinfectants, to reduce bacterial contamination in a fluid piping system. In the method of disinfection, a cylindrical bellows  12  as shown in FIG. 3 is fluidly connected between a first pipe  18  and a second pipe  20  within a fluid piping system. A sheath  32  is placed over the cylindrical bellows  12  to reduce deformation of the bellows  12  when sufficient heat is applied to the piping system to accomplish disinfection. Fluid or gag within the fluid piping system is heated to a temperature of at least 105 degrees Celsius, and applied to the system for a period of at least 20 hours, as prescribed by accepted standards. First pipe  18  and second pipe  20  are expanded, causing the cylindrical bellows  12  to compress within the sheath  32  which has been placed over and around the bellows  12  to restrict deformation of the bellows. 
     A particular feature of the present invention involves a removable connection of the bellows to the end of the pipe as shown in FIG.  2 . In FIG. 2 the bellows coupling member  26  is shown as male-threaded coupling member attached to the cylindrical bellows  12 . Pipe coupling member  22  is shown as a female-threaded coupling member attached to first pipe  18 . A male-threaded coupling member  26  is threadably received into the female-threaded coupling member  22 , which has a diameter greater than that of the bellows coupling member  26 . A removable connection is accomplished as the bellows coupling member  26  is threadably received within the pipe coupling member  22 . The expansion joint  10  of the present invention can be used in a modular fluid piping system, such as that described in U.S. patent application Ser. No. 09/206,904, since threaded coupling members  26  and  28  attached to the cylindrical bellows  12  facilitate interchangeable installation of a cylindrical bellows  12  within the system. The sheath  32  enclosing the cylindrical bellows  12  is also removable by means of the lengthwise split  34  and radial flexibility produced thereby. Pipe unions  36 , as shown in FIG. 4, utilized in a modular piping system, such as that described in U.S. patent application Ser. No. 09/206,904, facilitate installation of adjoining piping segments within the system, and facilitate installation and removal of the interchangeable cylindrical bellows  12  by allowing the bellows  12  to be threaded into the adjoining pipe segments  18  and  20  before the pipe segments are locked into place by attachment to pipe segments  42  and  44 , respectively, by the unions  36 . 
     Thus, although there have been described particular embodiments of the present invention of a new and useful “Expansion Joint for a Fluid Piping System,” it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.