Patent Publication Number: US-8979138-B2

Title: Pipe coupling having movable gripping bodies

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 13/470,522, filed May 14, 2012, which is a divisional of U.S. patent application Ser. No. 13/113,124, filed May 23, 2011, now U.S. Pat. No. 8,177,263, which is a divisional of U.S. patent application Ser. No. 12/119,661 filed May 13, 2008, now U.S. Pat. No. 7,950,701 which is based on and claims priority to U.S. Provisional Patent Application No. 60/938,003, filed May 15, 2007, all of which are hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to couplings for joining pipe elements in end-to-end relationship. 
     BACKGROUND OF THE INVENTION 
     Mechanical couplings for joining pipe elements end-to-end find widespread use throughout a broad spectrum of industries such as the chemical industry, the petroleum industry and mining, as well as in municipal water service and fire suppression systems for buildings and other structures. 
     An example of a prior art coupling currently in use is provided in U.S. Pat. No. 7,086,131, which discloses a coupling having a pair of coupling segments joined end-to-end by fasteners received in lugs at each end of the segments. A sealing member is positioned between the segments. The coupling is pre-assembled at the factory. The segments are designed and sized to receive pipe elements in the field which are inserted directly between the coupling segments in the pre-assembled state, without the need to disassemble and reassemble the coupling. After insertion of the pipe elements, the fasteners are tightened to effect a fluid-tight, mechanically restrained joint between the pipe elements. 
     While it is advantageous to pre-assemble such couplings because it saves time and thereby cost during construction, power tools are often used to tighten the fasteners for convenience, as they are faster and less fatiguing. Power tools are of limited value, however, where no source of electrical power or compressed air is available, even those tools which are battery operated. Furthermore, power tools which cause electrical sparking may not be used in environments, such as mines, where explosive conditions may exist. It would be advantageous to provide a pipe coupling which can be pre-assembled (and thereby secure the cost advantages and convenience of such couplings) while being easily manually tightened by workmen installing the couplings. It is further advantageous to decrease the stiffness of the joint formed by the coupling for certain applications. This can be accomplished by employing couplings according to the invention. 
     SUMMARY OF THE INVENTION 
     The invention concerns a pipe coupling for securing end portions of a pair of pipe elements together end-to-end. In one embodiment, the coupling comprises a plurality of segments connectable end-to-end surrounding a central space for receiving the pipe elements. Each segment has a pair of arcuate surfaces positioned in spaced relation, the arcuate surfaces facing the central space and being engagable with the pipe elements. Connection members are positioned at opposite ends of each of the segments for adjustably connecting the segments to one another. The connection members are adjustably tightenable for drawing the segments toward one another and into engagement with the pipe elements. Respective reaction surfaces are positioned on at least two of the connection members which face one another. The reaction surfaces face the central space. At least one gripping body is positioned between two of the segments. The gripping body has a pair of gripping surfaces positioned in spaced apart relation. The gripping surfaces face the central space for engagement with the pipe elements. A first pair of contact surfaces is positioned on the gripping body in facing relation with the reaction surfaces. Adjustable tightening of the connection members draws the coupling segments together. The contact surfaces interact with the reaction surfaces to move the gripping body into the central space for engagement of the gripping surfaces with the pipe elements. 
     In one embodiment, the reaction surfaces are angularly oriented with respect to the projections. Orientation angles for the reaction surfaces from about 30° to about 60° are feasible, with 45° being preferred. Alternately, the reaction surfaces may have a convex shape. The contact surfaces may also angularly oriented with respect to the projections. Orientation angles for the contact surfaces from about 30° to about 60° are feasible, with 45° being preferred. Alternately, the contact surfaces may have a convex shape. 
     In one embodiment of the coupling, the contact surfaces project radially outwardly away from the central space. In another embodiment, the gripping bodies have a second pair of contact surfaces. The first and second pairs of contact surfaces are positioned on opposite sides of the gripping body. 
     In another embodiment, the coupling comprises a plurality of segments connectable end-to-end surrounding a central space for receiving the pipe elements. Each segment has a pair of arcuate surfaces in spaced relation. The arcuate surfaces face the central space and are engagable with the pipe elements. Connection members are positioned at opposite ends of each of the segments for adjustably connecting the segments to one another. The connection members are adjustably tightenable for drawing the coupling segments toward one another and into engagement with the pipe elements. First and second reaction surfaces are positioned at opposite ends of each coupling segment in spaced relation. The reaction surfaces face the central space. First and second gripping bodies are positioned between the segments at opposite ends thereof. Each of the gripping bodies has a pair of gripping surfaces positioned in spaced relation to each other. The gripping surfaces face the central space and are engagable with the pipe elements. Each of the gripping bodies has a plurality of contact surfaces positioned in spaced relation. Each of the contact surfaces is engaged with one of the reaction surfaces of the segments. Each of the gripping bodies has end faces positioned opposite to one another. The segments have inwardly projecting shoulders positioned adjacent to the reaction surfaces. The shoulders are engagable with the end faces. Either the end faces or the shoulders or both are angularly oriented so as to cause rotation of the gripping bodies about an axis substantially perpendicular to the pipe elements when the coupling segments are drawn together. Adjustable tightening of the connection members draws the coupling segments together. The contact surfaces interact with the reaction surfaces to move the gripping bodies radially inwardly for engagement of the gripping surfaces with the pipe elements. 
     In one embodiment, the reaction surfaces extend in a tangential direction of the segments. In another embodiment, the gripping bodies comprise a channel adapted to receive a sealing member. The channel is skewed relatively to the gripping surfaces so as to substantially align with the sealing member upon rotation of the gripping bodies. 
     Another embodiment of the pipe coupling according to the invention comprises a plurality of segments connectable end-to-end. The segments surround a central space. Each segment has first and second arcuate grooves in spaced relation facing the central space. Connection members are positioned at opposite ends of each of the segments for adjustably connecting the segments to one another. The connection members are adjustably tightenable for drawing the segments toward one another. First and second reaction surfaces are positioned at opposite ends of each coupling segment in spaced relation to one another. The reaction surfaces face the central space. First and second gripping bodies are positioned between the segments at opposite ends thereof. Each of the gripping bodies has first and second arcuate grooves positioned in spaced relation. The grooves face the central space. Each of the gripping bodies has a plurality of contact surfaces positioned in facing relation with the reaction surfaces. Each of the contact surfaces is engaged with one of the reaction surfaces on each of the segments. First and second retainers are received within the grooves of the couplings. Each of the retainers comprises an annular band having a plurality of teeth extending radially inwardly. Each annular band is split so as to permit radial motion of the teeth when the band is radially compressed. The first retainer is received within the first grooves in the coupling segments and the gripping bodies and the second retainer is received within the second grooves in the coupling segments and the gripping bodies. The teeth of the first retainer are angularly oriented toward the teeth of the second retainer, and the teeth of the second retainer are angularly oriented toward the teeth of the first retainer. Adjustable tightening of the connection members draws the coupling segments together. The contact surfaces interact with the reaction surfaces to move the gripping bodies radially inwardly for compressing the retainers into engagement with the pipe elements. Preferably, the reaction surfaces extend in a tangential direction of the segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded isometric view of an embodiment of a coupling according to the invention; 
         FIGS. 2 and 3  are cross-sectional views of the coupling shown in  FIG. 1 ; 
         FIG. 4  is an isometric view of the coupling shown in  FIG. 1 ; 
         FIGS. 4A and 4B  are isometric views of alternate embodiments of a coupling according to the invention; 
         FIG. 5  is an exploded isometric view of another embodiment of a coupling according to the invention; 
         FIGS. 6 and 7  are elevational views of the coupling shown in  FIG. 5 ; 
         FIG. 8  is an isometric view of the coupling shown in  FIG. 5 ; 
         FIG. 9  is an isometric exploded view of another coupling embodiment according to the invention; 
         FIG. 10  is a front view of a component of the coupling shown in  FIG. 9 ; 
         FIG. 11  is an isometric view of the coupling shown in  FIG. 9 ; 
         FIG. 12  is a sectional view taken at line  12 - 12  of  FIG. 11 ; 
         FIGS. 13 and 14  are sectional views of the coupling shown in  FIG. 9 ; 
         FIG. 15  is an exploded view of another embodiment of the coupling according to the invention; 
         FIG. 16  is an exploded view of another embodiment of the coupling according to the invention; and 
         FIG. 17  is a sectional view of a portion of the coupling shown in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows an exploded isometric view of a coupling embodiment  10  according to the invention. Coupling  10  comprises a plurality of segments  12  and  14 . Segments  12  and  14  are connectable end-to-end to surround a central space  16 . Connection of the segments is effected by connection members  18  positioned at opposite ends of each of the segments  12  and  14 . In this embodiment, the connection members comprise projections  20  which extend outwardly from the ends of the segments. Projections  20  have apertures  22  adapting them to receive fasteners, such as bolts  24  and nuts  26 . The fasteners are adjustably tightenable and cooperate with the projections  20  for drawing the segments  12  and  14  toward the central space  16  upon tightening. 
     Each segment has a pair of arcuate surfaces  28 . Surfaces  28  are positioned in spaced relation to one another and face the central space  16 . The arcuate surfaces engage and retain pipe elements  30  (see  FIG. 4 ) when the fasteners connecting projections  20  are tightened to draw the segments toward each other. The arcuate surfaces may engage circumferential grooves in the pipe elements, plain ended pipe elements, flared end pipe elements or pipe ends having a shoulder. 
     Each segment also has at least one, but preferably a plurality of, reaction surfaces  32  positioned on the connection members  18 . In the embodiment shown in  FIG. 1 , two reaction surfaces  32  are positioned on each projection  20 . The reaction surfaces are angularly oriented with respect to the projections, and may have an orientation angle  34  from about 30° to about 60° and are inclined so as to face the central space  16 . Orientation angles of about 45° are preferred as explained below. 
     Coupling  10  also comprises one or more gripping bodies. In the example embodiment, two gripping bodies  36  and  38  are positioned between the segments  12  and  14  opposite to one another. Each gripping body has a pair of gripping surfaces  40 . Similar to the arcuate surfaces  28 , the gripping surfaces are positioned in spaced apart relation and face the central space  16 . Each gripping body has a pair of contact surfaces  42  positioned in facing relation with the reaction surfaces  32  on the projections  20  of the segments  12  and  14 . The contact surfaces are also angularly oriented with respect to the projections, and may have an orientation angle  44  from about 30° to about 60°. Orientation angles of about 45° are preferred as explained below. Preferably, the orientation angles  34  and  44  are complementary to one another, meaning that they have approximately the same angular orientation. 
     Upon assembly of the coupling  10 , a seal  46  is captured within the central space  16  by the segments  12  and  14  and the gripping bodies. Seal  46  ensures that the coupling  10  provides a fluid-tight joint between pipe ends. The seal  46  is sized so that, in an undeformed state, its outer circumference  48  supports the segments  12  and  14  and the gripping bodies  36  and  38  in spaced apart relation sufficient for pipe elements to be inserted into the central space  16  without disassembling the coupling. 
     Operation of the coupling is described with reference to  FIGS. 2 and 3 .  FIG. 2  shows the coupling  10  as received from the factory in the pre-assembled state, installation ready. In this configuration, the fasteners are not yet tightened, thereby allowing the segments  12  and  14  and the gripping bodies  36  and  38  to be positioned radially outwardly away from the central space  16  to allow pipe elements (not shown for clarity) to be inserted into the central space. As noted above, the seal  46  is sized to hold the segments and gripping bodies radially outwardly to facilitate pipe insertion. Upon insertion, the pipe elements engage the seal  46  which provides fluid tightness to the joint. Next, the bolts  24  and nuts  26  are tightened, drawing the segments  12  and  14  toward one another and the central space  16 . As the segments move, the arcuate surfaces  28  are brought into engagement with the outer surface of the pipe elements to retain them in the coupling. As shown in  FIG. 3 , motion of the segments  12  and  14  toward one another causes the gripping bodies  36  and  38  to move inwardly toward the central space  16 , in a direction substantially perpendicular to the motion of the segments. This permits the gripping surfaces  40  on the gripping bodies  36  and  38  to also engage the outer surface of the pipe elements. Motion of the gripping bodies toward the central space  16  is effected by the interaction of the contact surfaces  42  on the gripping bodies with the reaction surfaces  32  on the projections  20 . The angular orientation  44  and  34  of the contact surfaces and the reaction surfaces respectively, allows the forces between the surfaces to be resolved into a component directed toward the central space. This force, applied at the contact surfaces, causes the motion of the gripping bodies toward the central space. As noted above, orientation angles of about 45° are preferred for both the reaction surfaces and the contact surfaces. The 45° angles ensure that, during the motion of the segments  12  and  14  and the gripping bodies  36  and  38  toward the central space  16 , the arcuate surfaces  28  and the gripping surfaces  40  are at all times equidistant from the pipe elements  30  and contact the pipe elements substantially simultaneously. 
     As shown in  FIG. 2 , there are multiple gaps  17  between the end faces  19  of the gripping bodies  36 ,  38 , and shoulders  21  on segments  12  and  14 . The gaps  17  allow for the relative motion between the gripping bodes and the segments. The gaps are about one half the size of gaps between segments in prior art couplings and consequently the gripping bodies and segments have less tendency to pinch the seal  46  as the gaps  17  close to virtually line on line contact as shown in  FIG. 3 . This results in more uniform compression of seal  46  and the elimination of extrusion paths for the seal when under pressure. 
     It is advantageous to position the reaction surfaces  32  on the projections  20  and have the contact surfaces  42  project substantially radially outwardly away from the central space  16  so that the interface between the contact surfaces and the reaction surfaces is near the fastener (bolt  24 , nut  26 ) which joins the connections members  18  (in this example projections  20 ) to one another. Internal pressure within the coupling  10 , acting on the seal  46 , will force the segments  12  and  14  and the gripping bodies  36  and  38  away from the central space. Force applied to the gripping bodies within the coupling is transmitted to the segments at the interface between the contact surfaces  42  and the reaction surfaces  32 . Due to their angular orientation, the contact surfaces will tend to act like a wedge and force the projections  20  apart. By placing the interface close to the fastener joining the projections, the separation of the projections will be less than if the interface were farther from the fastener. The advantageous positioning of the contact surface-reaction surface interface minimizes the separation of the segments and allows the coupling to withstand higher pressures without leaking. Furthermore, by placing the reaction forces between the segments and the gripping bodies near the fasteners the distortion of the segments by the gripping bodies is lessened and the coupling better maintains its round shape. 
       FIG. 4A  illustrates another embodiment  11  of a coupling according to the invention. In this embodiment, the contact surfaces  42  on the gripping bodies  36  and  38  have a convex shape. This permits them to engage the reaction surfaces  32  tangentially when the segments  12  and  14  are drawn toward one another, resulting in reaction forces which cause motion of the gripping bodies toward the central space. The reaction surfaces  32  are angularly oriented.  FIG. 4B  shows another embodiment  13  wherein the reaction surfaces  32  have a convex shape and the contact surfaces  42  are angularly oriented. This again allows for tangential engagement between the reaction surfaces and the contact surfaces, resulting in reaction forces which cause motion of the gripping bodies toward the central space as the segments  12  and  14  are drawn toward each other. 
       FIG. 5  shows an isometric exploded view of another coupling embodiment  50  according to the invention. Coupling  50  has gripping bodies  36  and  38  with contact surfaces  52  positioned on opposite sides of the gripping bodies. Again, the contact surfaces are angularly oriented with respect to the connection members  18  and interface with reaction surfaces  54  positioned on the connection members  18 . Orientation angles  56  for the contact surfaces from about 30° to about 60° are advantageous for this coupling design. It is preferred that the orientation angle of the reaction surfaces  54  be approximately the same as the contact surfaces as shown in  FIG. 8 . 
     Operation of coupling  50  is similar to that of coupling  10  described above. As shown in  FIG. 6 , before tightening of fasteners  58  the segments  12  and  14  and the gripping bodies  36  and  38  are spaced outwardly away from the central space  16  so as to allow a pipe element to be inserted into the central space. Tightening of the fasteners as shown in  FIG. 7  draws the segments  12  and  14  toward one another and the central space, allowing the arcuate surfaces  28  to engage the pipe elements&#39; outer surface. Interaction between the contact surfaces  52  on the gripping bodies  36  and  38  and the reaction surfaces  54  on the segments  12  and  14  forces the gripping bodies to move inwardly toward the central space as the fasteners  58  are tightened. The inward motion of the gripping bodies allows their gripping surfaces  40  to engage the pipe elements  30  as shown in  FIG. 8 . 
       FIG. 9  shows an exploded view of another coupling embodiment  60  according to the invention. Coupling  60  comprises coupling segments  12  and  14 . The segments are arranged in facing relation and are joined end-to-end by connection members  18  positioned at opposite ends of each segment. In this embodiment, as with those previously described, the connection members comprise outwardly extending projections  20  which receive fasteners  58  that are adjustably tightenable. Tightening of the fasteners draws the coupling segments  12  and  14  toward one another and the central space  16 . 
     Each segment has inwardly facing arcuate surfaces  28  positioned in spaced relation to one another. The arcuate surfaces occupy positions between the ends of each segment. Reaction surfaces  32  are positioned in spaced relation at opposite ends of each coupling segment  12  and  14 . The reaction surfaces face inwardly toward the central space  16  and extend in a tangential direction around the segments. The reaction surfaces are angularly oriented as described below. 
     Gripping bodies  36  and  38  are positioned between the segments  12  and  14  at opposite ends of the coupling  60 . Each gripping body has inwardly facing gripping surfaces  40  arranged in spaced relation. Preferably, the gripping surfaces  40  align with respective arcuate surfaces  28  when the coupling is assembled as best shown in  FIG. 11 . With reference again to  FIG. 9 , each gripping body has contact surfaces  42  in spaced relation. Contact surfaces  42  face outwardly away from the central space  16  and engage respective reaction surfaces  32  on the segments  12  and  14 . The contact surfaces on the gripping bodies cooperate with the reaction surfaces on the segments such that, when the segments are drawn toward one another, for example, by the tightening of fasteners  58 , the gripping bodies are urged radially inwardly as explained further below. 
     A seal  46  is positioned between the coupling segments  12  and  14  and the gripping bodies  36  and  38 . Both the segments and gripping bodies have respective channels  62  and  64  positioned between the arcuate surfaces  28  and the gripping surfaces  40  which receive the seal. The inner circumference  66  of the seal  46  has inwardly facing sealing surfaces  68  and  70  which engage pipe elements joined by the coupling to form a fluid-tight seal. The seal  46  is sized so that, in an undeformed state, its outer circumference  72  supports the segments  12  and  14  and the gripping bodies  36  and  38  in spaced apart relation sufficient for pipe elements to be inserted into the central space  16  without disassembling the coupling. Preferably, the sealing member is a ring formed of an elastic, resilient material such as EPDM elastomer which deforms when the coupling segments are drawn toward one another by adjustably tightening the connection members  18 . 
       FIG. 11  shows the pipe coupling  60  in its pre-assembled state ready for use. To effect a fluid-tight joint connecting pipe elements in end-to-end relation, pipe elements  30  are inserted into the sealing member  46  as shown in  FIG. 12 , so that the segments straddle facing end portions of the pipe elements. The pipe elements are inserted to an extent such that grooves  74  in the outer surfaces of the pipe elements align with the arcuate surfaces of the segments (not shown) and the gripping surfaces  40  of the gripping bodies  36  and  38 . Insertion of the pipe elements to the proper depth may be facilitated by a pipe stop  76  positioned on the sealing member between the sealing surfaces  68  and  70 . The pipe stop projects inwardly to engage the ends of the pipe elements and limit the insertion depth as desired. 
       FIG. 13  shows a cross-sectional view of the coupling  60  with pipe element  30  inserted. Attention is drawn to the reaction surfaces  32  on segments  12  and  14  engaging the contact surfaces  42  on gripping bodies  36  and  38 . The reaction surfaces are angularly oriented so that when the fasteners  58  are tightened, drawing the segments  12  and  14  toward one another as shown in  FIG. 14 , the gripping bodies  36  and  38  are moved radially inwardly so that the gripping surfaces on the gripping bodies engage and grip the grooves  74  of the pipe elements  30  shown in  FIG. 12 . The motion of the segments  12  and  14  toward one another also causes the arcuate surfaces  28  (not shown) on each segment to engage and grip the grooves as well. The pipe elements are, thus, secured in end-to-end relation. The sealing member is deformed radially inwardly to force the sealing surfaces  68  and  70  into further engagement with the outer surfaces of the pipe elements. This configuration produces a relatively rigid joint. A more flexible joint can alternately be provided if the motion of the arcuate surfaces is limited so that they do not engage and clamp the floor of the groove. To this end, the travel of the gripping bodies is limited by the extent or length of the reaction surfaces and the contact surfaces. Limitation of motion of the arcuate surfaces on the segments toward the central space is preferably controlled by limiting the motion of the segments through contact of the connection members  18 . 
     As noted, the coupling embodiment  60  provides a substantially rigid joint for the pipe elements, i.e., the joint has significant stiffness about all three axes (bending, axial extension and torsion) to prevent significant angular deflection as well as axial movement (compression and extension) of the pipe elements relatively to one another. Torsional deflections are also inhibited. The rigidity of the joint is effected by the angularly oriented surfaces  78  and  80  positioned on each segment  12  and  14  adjacent to the connection members  18  as best shown in  FIG. 9 . The surfaces  78  and  80  on each segment have opposite slopes and are in facing relation with the angularly oriented surfaces on the adjoining segment. When the segments  12  and  14  are drawn toward one another by tightening of fasteners  58 , the angularly oriented surfaces on each segment engage one another and force the segments to rotate in opposite directions about an axis  82 , perpendicular to the pipe elements joined by the coupling. The rotation of the segments causes the arcuate surfaces  28  to forcibly engage the sidewalls of the grooves in the pipe elements and stiffen the joint, as described in U.S. Pat. Nos. 4,611,839, 4,639,020 and 5,758,907 hereby incorporated by reference. 
     To further enhance the rigidity of the joint between pipe elements formed by coupling  60 , the gripping bodies  36  and  38  may be designed as shown in  FIG. 9  such that their end faces  84  and  86  are angularly oriented relative to the gripping surfaces  40 . The angular orientation is best shown in  FIG. 10  for gripping body  36  which takes on a rhomboidal profile as a result. The end faces  84  and  86  engage inwardly projecting shoulders  88  on each segment  12  and  14  as the segments are drawn toward one another when forming a joint. The angular orientation of the end faces causes the gripping bodies  36  and  38  to rotate in opposite directions about an axis  90  as they are brought into contact with the shoulders  88 . Axis  90  is substantially perpendicular to the pipe elements being joined by the coupling segments  12  and  14 . The rotation of the gripping bodies causes the gripping surfaces  40  thereon to rotate and forcibly engage the sidewalls of the grooves in the pipe elements similar to the arcuate surfaces on the segments. To avoid rotationally deforming the seal  46 , the channels  64  in each gripping body are skewed in the opposite direction of rotation so that, when the gripping elements rotate about axis  90 , the channels  64  will align with the sealing members so that essentially only radial compression results, i.e., there is no significant twisting of the sealing member about axis  90 . 
     It is further observed that the angular orientation of the end faces  84  and  86  causes rotation of the segments  12  and  14  about axis  82 , thereby rendering the sloped surfaces  78  and  80  optional, and useful to enhance the rotation of the segments if necessary. 
     Rotation of the gripping bodies  36  and  38  about axis  90  may also be achieved by angularly orienting the inwardly projecting shoulders  88  as shown in  FIG. 15 , the orientation angle  92  of the shoulder forcing rotation of the gripping bodies as the segments  12  and  14  are drawn together, forcing engagement between the shoulders  88  and the end faces  84  and  86  of the gripping bodies. It is also possible to combine the features of  FIGS. 9 and 15  and have both the end faces  84  and  86  angularly oriented as well as the shoulders  88 . 
     It is also feasible to provide angularly oriented surfaces on each segment which have opposite slopes. Such couplings will also provide a rigid joint, but the interaction of the surfaces causes the couplings to slide in opposite directions and thereby engage the sidewalls of the grooves. If it is desired to allow some degree of bending flexibility to the joint, the surfaces adjacent to the connection members are made with no slope, i.e., substantially flat. 
       FIG. 16  shows an exploded view of another coupling embodiment  94  according to the invention. Coupling  94  is used to couple plain end pipe elements together, i.e., pipes having no grooves, beads, enlargements or other features near the ends to facilitate engagement with the coupling. Many of the components of this embodiment are similar to coupling  60  and will not be described in detail. Note also that the sealing member  46  shown in  FIG. 1  is not shown in  FIG. 6  for clarity, although the same or a similar sealing member is also used with coupling  94 . 
     To enable the coupling  94  to grip plain end pipe elements, two retainers  96  and  98  are used. Each retainer comprises an annular band  100  which has a plurality of flexible, resilient teeth  102 . The teeth project radially inwardly for engagement with the pipe elements as described below. The teeth are also angularly oriented out of the plane of the band  100 , with the teeth on retainer  96  being angled toward the teeth on retainer  98  and vice versa. The angular orientation of the teeth allows the pipe elements to be inserted into the coupling, but prevents the pipe elements from being withdrawn when the teeth forcibly engage the pipe elements as described below. Band  100  is split, as evidenced by the gap  104 . This gap permits the band to be compressed radially to allow the teeth to engage the pipe elements. 
     The retainers are received within grooves  106  and  108  in segments  12  and  14  and grooves  110  and  112  in the gripping bodies  36  and  38 . Preferably, when assembled, the grooves in the segments align with the grooves in the gripping bodies. As shown with reference to  FIGS. 16 and 17 , when the pipe elements  30  are inserted into the coupling  94  and the fasteners  58  are tightened, the segments  12  and  14  are drawn together and the gripping bodies  36  and  38  move inwardly in response to the interaction of the reaction surfaces  32  with the contact surfaces  42 . The inward motion of the grooves  106 ,  108 ,  110  and  112  compresses the bands  100  of retainers  96  and  98  inwardly so that teeth  102  engage the surfaces of pipe elements  30 . Because the teeth are angled they deflect inwardly and permit the pipe elements to be inserted into the coupling. But when force is applied which tends to remove the pipe elements from the coupling, the teeth prevent this motion due to the self-jamming characteristics of the angled teeth. 
     Retainers  96  and  98  preferably have a plurality of tabs  114  which project outwardly from the band  100 . As shown in FIG.  16 , the tabs engage the grooves  106  and  108  of the segments as well as grooves  110  and  112  of the gripping bodies and provide a degree of radial flexibility to the retainer. This added flexibility permits the segments to be joined in what is known as “pad-to-pad” relation wherein the connection members  18  on the segments abut one another when the fasteners  58  are tightened in spite of dimensional variations in the segments and pipes. It is advantageous that the segments join pad-to-pad as it provides a readily identifiable visual indication that the fasteners are fully tightened and thereby avoids the need for torquing the fasteners to a particular value as proof of completion of a fluid-tight joint. Avoiding the need for torque measurements simplifies installation of the coupling, as a torque wrench is not necessary. 
     Couplings according to the invention realize an advantage through the use of the moving gripping bodies which allows them to be installed from the pre-assembled state easily using hand tools. The movable gripping bodies reduce the torque required to bring the segments together and grip the pipe elements to effect a fluid-tight joint.