Abstract:
Push-fit pipe fitting device assemblies having a) a main body comprising one or more tubular portions, a first end of each of the tubular portions is connected either to a first end of another tubular portion or to another push-fit pipe fitting device assembly; and each of second ends of the tubular portions is configured to host a pipe; b) one or more tubular inserts, wherein the one or more tubular inserts are fittingly disposed inside tubular portions of the main body; c) one or more nuts, the one or more nuts is fittingly disposed over second ends of the main body; d) one or more grip rings, wherein the one or more grip are fittingly disposed over second ends of the tubular inserts, and inside the one or more nuts; and e) one or more elastomeric sealing rings disposed at each end of the one or more tubular inserts.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a National Stage entry of International Application No. PCT/IL2009/000079 filed Jan. 20, 2009, which claims priority to U.S. Provisional Patent Application Ser. No. 61/041,490, filed Apr. 3, 2008, the disclosure of the prior applications is hereby incorporated in its entirety by reference. 
     The unique grip ring is described in PCT application PCT/IL2008/001480, filed Nov. 1, 2008, by Gershkovich et al, the disclosure of which is included herein by reference for all purposes as if entirely set forth herein. The grip ring enables a quick plug-in of a push-fit pipe into a fitting device. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to grip rings for mechanical pipe fitting (coupling) devices and more particularly the present invention relates to mechanical push-fit pipe fitting device assemblies utilizing unique grip ring, pipe insert and a ring sealer. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     A plug-in pipe fitting device assembly, also referred to as a push-fit pipe fitting device, typically includes a base body, an elastomeric sealing ring, an annular body which can be connected to the base body and a grip ring which locks in position a pipe end inserted into the push-fit fitting device. A grip ring typically enables smooth insertion of a pipe into the fitting device but disallows the removal of the pipe from the fitting device. The grip ring of the present invention provides an improved locking mechanism that enables a continuous mechanical gripping of a pipe end, pushed into the push-fit fitting device. The sealing ring enables a hermetic sealing of the mechanical joint made with at least one pipe end, indifference of the materials the pipes are made of, whether metallic or non-metallic. 
     Many mechanical jointing applications are used in pipe systems carrying liquids at temperatures up to about 110° C. and higher, and pressures up to approximately 1000 psi. Furthermore, coupling devices of this type are typically used with water pipe systems but can also used with fluids of all types, including toxic and volatile chemicals. 
     To withstand different pressures, pipes are made of different thicknesses. Typically the external diameter of water pipes is constant, and the thickness varies inwardly, towards the longitudinal axis of the pipe. To differentiate between the pipes, having the same external diameter, the pipes typically are manufactured with different colors, whereas each internal diameter is represented by a given color. 
     There is a further need for, and it would be advantageous to have, a push-fit fitting device having ring sealers that provide sealing of the mechanical joints between the push-fit fitting device and the inserted pipe, and grip rings, such as provided by PCT application PCT/IL2008/001480, that lock the inserted pipe in an increased force and increases the grip locking force when the inserted pipe attempts to move out of the fitting device. 
     SUMMARY OF THE INVENTION 
     The principal intentions of the present invention include proving push-fit pipe fitting devices and in particularly for push-fit pipe fitting devices, the fitting device including a body, a pipe insert, a nut, a ring sealer and a grip ring at each end of the fitting device. 
     Generally, the push-fit pipe fitting devices of the present invention will be described in terms of a fitting device that couples to two pipes, but the pipe fitting devices of the present invention are not limited to coupling two pipes and the push-fit pipe fitting devices may come in various fitting configurations including the coupling of three pipes, four pipes or any other number of pipes. 
     According to the teachings of the present invention there is provided a push-fit pipe fitting device assembly, according to embodiments of the present invention. The push-fit pipe fitting device connects at least two pipes, whereas after connection, the tangential longitudinal axis of the pipe fitting device is substantially tangential longitudinal axes of the pipes. The push-fit pipe fitting device assembly includes a main body, a tubular insert, a nut having a wide end and a narrow end, a grip ring having a wide end and a narrow end, and one or more elastomeric sealing rings. 
     The main body includes one or more tubular portions having a first end, a second end and a longitudinal axis. Typically, with no limitation on the number of tubular portions, the main body includes two tubular portions forming a single tubular body. The first end of each of the tubular portions is rigidly connected either to a first end of another tubular portion or to another plumbing connecting means, such as standard thread. Each of the second ends of the tubular portions is an open end, designed to host a pipe, which is to be inserted through the second end of the tubular portion. 
     The tubular insert includes two portions, having a first end of and a second end. The tubular insert is fittingly disposed inside each of the tubular portions of the main body. The nut having a wide end and a narrow end is fittingly disposed over, each of the second ends of the main body. The grip ring is fittingly disposed over each of the second ends of the tubular portions, and inside the nut. The one or more elastomeric sealing rings are fittingly disposed at each end of the tubular inserts. 
     An aspect of the present invention is to provide a push-fit pipe fitting device assembly, wherein when the fitting device is assembled, the sealing rings are fittingly disposed in respective grooves approximately at the ends of each of the tubular inserts. The first portion of each of the tubular inserts is respectively inserted into the internal space of the main body, through the second end of the tubular portion of the main body, and thereby sealingly locking the tubular insert into the main body. The grip rings are then loosely disposed over the second portion of each of the tubular insert. The wide end of each of the nut is respectively inserted over the grip ring and forcefully locking onto a radially fitted nut-locking-mechanism, disposed on the external surface of the main body. The narrow end of each of the nuts is smaller in diameter than the narrow end of the respective grip ring, thereby locking the grip ring inside the fitting device assembly. The narrow end of each of the nuts is larger in diameter than the second portion of the respective tubular inserts. 
     According to further teachings of the present invention the grip ring further include an annular body, a cylindrical inner surface, an external surface having a conical like structure, a slit cut through the annular body, extending from the narrow end to the wide end, and at least one annular gripping tooth disposed on the inner surface of the grip ring. The smaller most diameter of the annular gripping tooth, the grip ring being in a non compressed state, is smaller than the external diameter of the inserted pipe. 
     According to further teachings of the present invention, each of the tubular inserts further includes an inner surface, an external surface, a pipe stopper, one or more grip ring stoppers disposed on the pipe stopper, and one or more annular teeth disposed at the second end of the second portion of the tubular insert. The pipe stopper separates the first and second portions of the tubular insert, wherein the pipe stopper extends outwardly substantially perpendicular to the external surface of the tubular insert. The one or more grip ring stoppers, disposed on the pipe stopper, extend substantially perpendicular to the pipe stopper and substantially parallel to the external surface of the tubular insert, towards the second end of the second portion of the tubular insert. 
     An aspect of the present invention is to provide a push-fit pipe fitting device assembly, wherein when the pipe is forcefully inserted into the end of the fitting device, the internal surface of the pipe slides over the second end of the second portion of the tubular insert and over the one or more sealing rings disposed at the second end of the second portion of the tubular insert, thereby obtaining a full sealing of the inside of the pipe. As the pipe continues to move in, the pipe pushes the grip ring until the grip ring is stopped by the grip ring stopper. As the pipe continues to move in, the external surface of the pipe slides over the at least one annular gripping tooth of the grip ring and expands the longitudinal opening of the grip ring with respect to the longitudinal axis of the pipe. The pipe proceeds to move in until the rim of the pipe reaches the pipe stopper. The annular teeth, disposed at the second end of the second portion of the tubular insert, penetrate into the internal surface of the pipe, thereby grip the pipe. 
     An aspect of the present invention is to provide a push-fit pipe fitting device assembly, wherein after the pipe has reached the stopper of each of the tubular segment of the fitting device, when a forceful outward movement is applied to one of the pipes with respect to the other pipes, the forceful outward movement activates the gripping operation of the fitting device assembly. 
     The gripping operation of the fitting device assembly of the present invention includes the steps of:
         a) the conical external surface of the grip ring encounters an inner conical surface of a respective nut;   b) the inner conical surface of the nut pushes the grip ring inwardly towards the longitudinal axis of the pipe, and thereby compressing the grip ring; and   c) at least one of the annular gripping tooth move forcefully inwardly towards the longitudinal axis of the pipe, thereby the annular gripping tooth penetrates into the external surface of the pipe, and thereby strengthening the grip on the pipe.       

     It should be noted that the grip ring and the tubular insert form a U-shaped assembly, wherein said U-shaped assembly grips the pipe about the rim of the pipe, wherein the rim of the pipe is disposed inside the U-shaped assembly. 
     It should be noted that the diameter of the external surface of the tubular insert, the internal diameter of the grip ring and the inner diameter of the opening of the narrow of end of the nut are designed to match the external diameter of the pipe. 
     In variations of the present invention, two or more of the second ends of the main body are designed to grip pipes with different external diameter. 
     In variations of the present invention, at least one of the elements of the push-fit pipe fitting device assembly are selected from the group consisting of a tubular insert, a grip ring and a nut, has a color representing the external diameter of the target pipe. 
     According to further teachings of the present invention, each of the nuts further includes multiple windows and multiple slits extending from the rim of the wide end towards the narrow end, not reaching said narrow end, thereby forming bendable portions between two adjacent slits. In variations of the present invention, the length of the slits is less than half the distance from the wide end to the narrow end. 
     According to further teachings of the present invention, the nut-locking-mechanism includes protrusions extending from the external surface of the main body. When the rim of the wide end of the nut reaches the protrusions, the bendable portions bend outwardly, with respect to the longitudinal axis of the fitting device, thereby sliding over the protrusions/when the windows reach their respective protrusions, the bendable portions bend back inwardly, with respect to the longitudinal axis of the fitting device, thereby locking the windows over the protrusions and thereby locking the nut onto the main body. 
     It should be noted that the external contour of the external surface of the main body, where the nut-locking-mechanism is disposed, forms a radially symmetric polygon-like shape, the cross section plane of the external contour being perpendicular to the longitudinal axis of the fitting device. 
     It should be further noted that the internal contour of the internal surface of the nut, where said windows are disposed, forms a radially symmetric polygon-like shape, the cross section plane of the internal contour being perpendicular to the longitudinal axis of the fitting device. The internal contour of the internal surface of the nut is designed to match the external contour of the external surface of the main body, where the nut-locking-mechanism is disposed, and thereby preventing radial movement of the nut with respect to the main body. 
     It should be further noted that the alignment between the external surface of the main body with the internal surface of the nut, brings the windows to locking alignment with the protrusions. 
     According to further teachings of the present invention, the main body further includes ribs extending from each of the second ends of the main body. The external surface of each of the ribs substantially coincides with the corresponding side of the polygon-like external contour of the external surface of the main body. The internal contour of the ribs, the cross section plane of the internal contour being perpendicular to the longitudinal axis of the fitting device, forms a radially asymmetric polygon-like shape. 
     The external contour of the pipe stopper of the tubular insert forms a radially asymmetric polygon-like shape, wherein the internal contour of the internal surface of the ribs is designed to match the external contour of the pipe stopper, preventing radial movement of the tubular insert with respect to the main body. The asymmetric contour of the pipe stopper, that directionally guides the insert during insertion of the pipe, ensures that the pipe stopper supporting ribs do not obstruct the windows of the nut or the gaps between the ribs of the main body. 
     An aspect of the present invention is to provide a push-fit pipe fitting device assembly, wherein the hardness of the materials from which the gripping teeth of the grip ring and the gripping teeth of the tubular insert are made, is greater than the hardness of the material from which the pipe is made. 
     It should be noted that the tubular insert can be viewed while and after the pipe is inserted into the fitting device assembly. 
     It should be further noted that the pipe can be viewed while and after the pipe is inserted into the fitting device assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become fully understood from the detailed description given herein below and the accompanying drawings, which are given by way of illustration and example only and thus not limitative of the present invention, and wherein: 
         FIG. 1  is a side view illustration of a push-fit pipe fitting device assembly, according to embodiments of the present invention. 
         FIGS. 2   a  and  2   b  are perspective view illustrations of the push-fit pipe fitting device assembly shown in  FIG. 1 , having two pipes being pushed into the fitting device. 
         FIG. 3  is a side view illustration of a push-fit pipe fitting device assembly, according to embodiments of the present invention, wherein the fitting device assembly is designed to push-fit-connect three pipes. 
         FIG. 4  is a side view illustration of a push-fit pipe fitting device assembly, according to embodiments of the present invention, wherein the fitting device assembly is designed to push-fit-connect one pipe. 
         FIG. 5  is an exploded side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 1 . 
         FIG. 6  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 1 , having one side assembled and the other side in an exploded view. 
         FIG. 7  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 6 , wherein the ring sealers are assembled. 
         FIG. 8  is a front view illustration of the main body of the push-fit pipe fitting device assembly shown in  FIG. 1 . 
         FIG. 9  is a side perspective view illustration of the push-fit pipe fitting device assembly shown in  FIG. 7 . 
         FIG. 10  is a side perspective view illustration of the push-fit pipe fitting device assembly shown in  FIG. 7 , wherein the pipe insert is fully inserted into the main body of the push-fit pipe fitting device assembly. 
         FIG. 11  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 7 , wherein the pipe insert, including a grip ring, is partially inserted into the main body of the push-fit pipe fitting device assembly. 
         FIG. 12  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 7 , wherein the pipe insert, including a grip ring, is fully inserted into the main body of the push-fit pipe fitting device assembly. 
         FIG. 13  is a side perspective view illustrations of the nut of the push-fit pipe fitting device assembly shown in  FIG. 1 . 
         FIG. 14  is cross section AA′ broken view illustration of the end of the push-fit pipe fitting device assembly shown in  FIG. 1 , being fully assembled. 
         FIG. 15  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 1 , being fully assembled. 
         FIG. 16   a  is a cross section, broken view illustration of a portion of the end the push-fit pipe fitting device assembly shown in  FIG. 1 , being fully assembled with a pipe. 
         FIG. 16   b  illustrates forces relations between the grip ring and the pipe insert, when the pipe is pushed into the push-fit pipe fitting device assembly shown in  FIG. 1 . 
         FIG. 17   a  is a cross section, broken view illustration of the portion of the end the push-fit pipe fitting device assembly shown in  FIG. 16   a , wherein the pipe has been pulled. 
         FIG. 17   b  illustrates forces relations between the grip ring and the pipe insert, when the pipe is pulled out of the push-fit pipe fitting device assembly shown in  FIG. 1 . 
         FIG. 18  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 1 , being fully assembled, including a pipe inserted into the fitting device. 
         FIG. 19  is a detailed view of window “A” shown in  FIG. 18 . 
         FIG. 20  is a side view illustration of the push-fit pipe fitting device assembly, according to embodiments of the present invention, wherein each side is designed for a different pipe diameter size. 
         FIG. 21  is a side view illustration of the push-fit pipe fitting device assembly shown in  FIG. 20 , having one side assembled and the other side in an exploded view. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided, so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The methods and examples provided herein are illustrative only and not intended to be limiting. 
     By way of introduction, the principal intentions of the present invention include proving push-fit pipe fitting device assemblies designed to connect and seal pipes, in a pressurized system, typically a water pipe system, for either cold or hot water. The push-fit pipe fitting device assembly will be described in terms of being designed to connect and seal two pipes, but the push-fit pipe fitting device assembly of the present invention is not limited to connecting just two pipes, and can be designed to connect any number of plastic pipes. The pipes for which the push-fit pipe fitting device assembly of the present invention is designed to connect and seal are typically, but not exclusively, plastic pipes. 
     Reference is now made to the drawings.  FIG. 1  is a side view illustration of push-fit pipe fitting device assembly  100 , according to embodiments of the present invention. Fitting device  100  includes main body  110 , pipe insert  150 , two nuts  120 , two grip rings  130  and four ring sealers  140 .  FIG. 2  is a perspective view illustration of push-fit pipe fitting device assembly  100 , having two pipes ( 50   a ,  50   b ) being respectively pushed into each end of fitting device  100 . 
     By way of example, with no limitation upon other variations of the present inventions, the present invention will be now described primarily through push-fit pipe fitting device assemblies for connecting two pipes. But the present invention is not limited to push-fit pipe fitting device assembly for connecting two pipes, and in other variations of the present invention the push-fit pipe fitting device assembly can connect any number of pipes. For example,  FIG. 3  is a perspective view illustration of push-fit pipe fitting device assembly  300  for connecting three pipes. In another example,  FIG. 4  is a perspective view illustration of push-fit pipe fitting device assembly  400  for connecting one pipe, while on the other side another conventional plumbing unit can be attached onto a prior art plumbing connecting means such as threads  410 . 
     Reference is also made to  FIGS. 5-12 :  FIG. 5  is an exploded side view illustration of fitting device  100 ;  FIG. 6  is a side view illustration of fitting device  100 , having one side assembled and the other side in an exploded view;  FIG. 7  is a side view illustration of fitting device  100 , wherein ring sealers  140  are assembled;  FIG. 8  is a front view illustration of main body  110  of push-fit pipe fitting device  100 ;  FIG. 9  is a side perspective view illustration of fitting device  100 ;  FIG. 10  is a side perspective view illustration of fitting device  100 , wherein tubular insert  150  is fully inserted into main body  110 ;  FIG. 11  is a side view illustration of fitting device  100 , wherein tubular insert  150 , including grip ring  130 , is partially inserted into main body  110 ; and  FIG. 12  is a side view illustration of fitting device  100 , wherein tubular insert  150 , including grip ring  130 , is fully inserted into main body  110 . 
     Main body  110  is the interface part that symmetrically connects with identical mechanisms the two pipes. The symmetry can be broken only when fitting pipes of different diameters, whereas on the diameters of respective parts differ on both sides of main body  110 . The description will hereon be in terms of connecting a pipe to one side of main body  110 , wherein the same is applied to the other side of main body  110 . 
     Main body  110  includes an inner opening  117  ( FIGS. 8 ,  9 ) into which tubular insert  150  is inserted. Main body  110  further includes a ribbed structure which includes ribs  112  having gap  114  between adjacent ribs, and protrusions  118 , whereas each protrusion  118  is disposed on to outer surface of the ribs structure, behind each gap  114 . Ribs  112  include thin ribs  113  and thick ribs  111 ; whereas ribs  112  form a polygon-like radial symmetric external contour  115  and a polygon-like radial asymmetrical inner contour  116 , as illustrated in  FIG. 8 . In the example shown in the figures, main body  110  includes a ribs structure which includes 6 ribs  112  generally forming a hexagon structure. It should be noted the contours refer to the contour formed by a cross section plane perpendicular to longitudinal axis  105  of fitting device  100 . 
     Tubular insert  150  includes annular ribs  154  ( FIG. 6 ), on which corresponding grooves in ring sealers  140  are disposed, stopper  152  and annular teeth  158 , disposed on the end of tubular insert  150  that is opposite to the side of main body  110 . Stopper  152  includes supporting ribs  156  that protrude out of stopper  152 . The external contour of stopper  152  fits inner contour  116  of the ribs structure of main body  110 , and since the contours are asymmetric, the insertion of tubular insert  150  inside the ribs structure of main body  110  becomes directionally dictated. The position of supporting ribs  156  on stopper  152  coincide with the position of thin ribs  113  on the ribs structure of main body  110 . The width of supporting ribs  156  is not larger than the width of thin ribs  113 , and the ribs structure of stopper  152  does not allow supporting ribs  156  to block gap  114 . 
     Grip ring  130  has an annular structure, whereas in a longitudinal cross section of grip ring  130 , external surface  132  of the grip ring  130  has a conical like structure. On the inner surface of grip ring  130  multiple annular gripping teeth  134  are disposed. Annular grip ring  130  needs to be radially deformable and gap  136  allows grip ring  130  to be compressed. 
     Reference is also made to  FIG. 13 , which is a side perspective view illustrations of nut  120  of push-fit pipe fitting device assembly  100 . Nut  120 , includes an external conical surface, internal surfaces  125 , an internal conical surface  127 , windows  122 , a step stopper  124 , opening  121  into which a pipe is inserted, slits  128  and portions  126  disposed between slits  128 . Slits  128  enable each portion  126  to bend individually, nut  120  being made of materials with the required elasticity. Internal surfaces  125  form a radial contour that fits external contour  115  ( FIGS. 8 ,  9 ) formed by the external surfaces of ribs  112 . Windows  122  are disposed between adjacent surfaces  125 . The inclination angle and position of conical surface  127  matches the inclination angle of external surface  132  of grip ring  130 . 
     The assembly of all sides of push-fit pipe fitting device assembly  100  is similar and hence the hereon assembly description of one side of fitting device  100  applies to all sides. The assembly starts by disposing ring sealers  140  onto tubular insert  150 , whereas tubular insert  150  includes two pairs of annular ribs  154  ( FIG. 6 ), one on each side of tubular insert  150 , on which corresponding grooves in ring sealers  140  are disposed ( FIG. 7 ). 
     It should be noted that ring sealer  140  is the preferred ring sealer of the present invention, but the present invention is not limited to ring sealer  140  and any ring sealer (or combination of ring sealers) can be used, providing corresponding adjustments to tubular insert  150  are made. 
     Reference is also made to  FIG. 14 , which is cross section AA′ ( FIG. 1 ) broken view illustration of the end of push-fit pipe fitting device assembly  100 , being fully assembled, and to  FIG. 15 , which is a side view illustration of fitting device  100 , being fully assembled. 
     Tubular insert  150  is then inserted into opening  117  in main body  110  ( FIGS. 9 and 10 ) wherein ring sealer  140   a  seals tubular insert  150  inside main body  110  ( FIG. 14 ). The shape of the external contour of stopper  152  fits inner contour  116  of the ribs structure of main body  110 , and since both contours are asymmetric, the insertion of tubular insert  150  inside the ribs structure of main body  110  is directionally dictated, and any relative rotational movement between tubular insert  150  and main body  110  is prevented. The position of supporting ribs  156  on stopper  152  coincide with the position of thin ribs  113  on the ribs structure of main body  110 , and gaps  114  remain open. 
     Grip ring  130  is then passed over the open end of tubular insert  150  having the wider side of grip ring  130  facing main body  110 . Following grip ring  130 , nut  120  is then passed over the open end of tubular insert  150 , and forcefully pushed onto protrusion  118  of main body  110 . The movement of grip ring  130  is stopped by ribs  112 . Inner surfaces  125  of nut  120  internal surfaces  125 , having a contour that fits external contour  115  formed by the external surfaces of ribs  112 , directionally guide the insertion of nut  120  onto the ribs structure of main body  110 . When portions  126  disposed between slits  128  of nut  120  reach protrusions  118  of main body  110 , portions  126  slightly bend outwards, with respect to longitudinal axis  105  of fitting device  100  (see  FIG. 14 ), slide over protrusions  118  and when windows  122  pass over protrusions  118 , portions  126  bend back towards surface  119  of main body  110 , thereby locking nut  120  to main body  110 . Tubular insert  150  still has the freedom to move a few millimeters inside main body  110 , along longitudinal axis  105  of fitting device  100 . 
     Reference is also made to  FIGS. 16   a - 19 :  FIG. 16   a  is a cross section, broken view illustration of a portion of fitting device  100 , being fully assembled with a pipe;  FIG. 17   a  is a cross section, broken view illustration of the portion of the end fitting device  100  as shown in  FIG. 16   a , wherein the pipe has been pulled;  FIG. 18  is a side view illustration of fitting device  100 , being fully assembled, including inserted pipe  50 ; and  FIG. 19  is a detailed view of window “A” shown in  FIG. 18 . 
     To attach a pipe to an end of push-fit pipe fitting device  100 , pipe  50  of compatible diameter is pushed into the opening at end of fitting device  100 . Pipe  50  slides over annular teeth  158  disposed on the end of tubular insert  150 , then slides over and squashes ring sealer  140   b , thereby obtaining a full sealing of the inside of pipe  50 . As pipe  50  continues to move in, the external surface of pipe  50  reaches gripping teeth  134  of grip ring  130 , slides over the first gripping tooth  135  and expands gap  136  of grip ring  130  and thereby expand the radius of grip ring  130 . Pipe  50  proceeds moving in sliding over gripping teeth  134  until the rim of pipe  50  reaches stopper  152 . As pipe  50  slides into pipe fitting device  100 , pipe  50  can be viewed and monitored through windows  122 . Reference is also made to  FIG. 16   b , which illustrates forces relations between grip ring  130  and tubular insert  150 , when pipe  50  is pushed into the push-fit pipe fitting device  100 , and to  FIG. 17   b , which illustrates forces relations between grip ring  130  and tubular insert  150 , when pipe  50  is pulled out of push-fit pipe fitting device  100 . When pipe  50  is pushed into fitting device  100 , in direction  55 , forces convey from grip ring  130  towards tubular insert  150 , in direction  175 . When pipe  50  is pulled out of fitting device  100 , in direction  56 , forces convey from tubular insert  150  towards grip ring  130 , in direction  176 . 
     As pipe  50  reaches stopper  152 , annular teeth  158  penetrate into the internal surface of pipe  50  ( FIG. 16   a ). When pipe  50  is pulled outwardly from fitting device  100 , annular teeth  158  further penetrate into the internal surface of pipe  50  ( FIG. 17   a ) and in turn, pipe  50  pulls tubular insert  150  outwardly from fitting device  100 . When supporting ribs  156  of tubular insert  150  reach grip ring  130 , which moves along with tubular insert  150  until external surface  132  of grip ring  130  reaches internal surface  127  of nut  120 . Surface  127  pushes external surface  132  inwardly, thereby forcing grip ring  130  to slightly close gap  136  ( FIGS. 7 ,  11 ) of grip ring  130 , and thereby gripping teeth  134  further penetrate into the external surface of pipe  50 . Hence, pipe  50  is now held by annular teeth  158 , gripping the internal surface of pipe  50  and by gripping teeth  134 , gripping the external surface of pipe  50 . 
     As pipe  50  is being further pulled outwardly from fitting device  100 , annular teeth  158  and gripping teeth  134  further penetrate into surface of pipe  50 , while grip ring  130 , may further move outwardly as the diameter of grip ring  130  gets smaller. Grip ring  130  may reach a final stop when reaching stopper step  124 . 
     It should be noted that through out the push/pull processes of pipe  50  in/out of fitting device  100 , tubular insert  150  can be viewed through windows  122 , including stopper  152 . 
     Since typically the external diameter of water pipes is constant, and the thickness of the pipe varies inwardly, towards the longitudinal axis of the pipe, tubular inserts are provided by the present invention, wherein pipes of different diameters can be connected by a single tubular insert. Reference is now made to  FIG. 20 , which is a side view illustration of push-fit pipe fitting device assembly  200 , according to embodiments of the present invention, wherein each side of fitting device  200  is designed for a different pipe diameter size, and to  FIG. 21 , which is a side view illustration of fitting device  200 , having one side assembled and the other side in an exploded view. Referring also back to  FIG. 2 , while in device  100  diameter D of pipe  50   a  is substantially the same as diameter D of pipe  50   b , in device  200 , diameter D of pipe  50   a  differs from diameter D of pipe  50   b.    
     In embodiments of the present invention, tubular inserts that are designed to fit a different combination of pipe sizes, are fabricated in a different color. 
     Hence to know the size of each end of a particular tubular insert ( 150 ,  250 ), one can either measure the diameter of each end of that tubular insert ( 150 ,  250 ), or interpret the tubular insert color. When assembled inside a push-fit pipe fitting device ( 100 ,  200 ) of the present invention, the color of a tubular insert ( 150 ,  250 ) can also be viewed through windows ( 122 ,  222 ). 
     It should be noted that to change the size of a pipe on either end of pipe fitting device  100 , only corresponding tubular insert  250 , grip ring  230  and corresponding nut  220  need to be replaced. 
     In embodiments of the present invention, the size of the nut is imprinted or molded on the external surface of the nut. For example, nut  120  of pipe fitting device  100  fit pipes  50   b , having a 20 mm internal diameter, and nut  220  of pipe fitting device  200  fit pipes  50   a , having a 16 mm internal diameter. 
     The invention being thus described in terms of several embodiments and examples, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art.