Abstract:
A coupling for the end of a corrugated pipe has two catches integrally moulded with the housing of the coupling. The catches are hinged at one end and have a tooth at their other end that engages between the corrugations on the pipe. Two undulating webs link the other end of the catches with the housing to provide an additional resilient restoring force acting on the catches.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to pipe couplings.  
           [0002]    Connection to a corrugated pipe or conduit can be made by means of a coupling in which the end of the pipe is inserted, the coupling having a locking member in the form of a resilient catch or tooth that engages between corrugations to prevent the pipe and coupling being pulled apart after assembly. Couplings of this kind are described, for example, in U.S. Pat Nos. 5,094,482, 5,041,256, GB2225550, U.S. Pat. Nos. 5,150,930 and 4,923,227 and are sold by Adaptaflex Limited of Coleshill, Birmingham, UK. Because the catch must engage between corrugations to lock the conduit in the coupling, the conduit should be pulled back slightly. after insertion to ensure that the catch has fully engaged. If this is not done, there is a risk that the catch might sit on a corrugation in an outward position and not be properly locked. If a coupling is left in this state for some time, the catch may be permanently deformed to lie in the outward position and not provide any significant resilient locking force. This may allow the conduit subsequently to be pulled from the coupling.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    It is an object of the present invention to provide an alternative pipe coupling.  
           [0004]    According to one aspect of the present invention there is provided a coupling for a corrugated pipe, the coupling including a housing and a catch member mounted at one end with the housing and arranged to provide a resilient inwardly directed locking force at its opposite end to engage between corrugations on the pipe, the coupling including a resilient member extending between the housing and the opposite end of the catch member to provide an additional inwardly-directed restoring force on the catch member.  
           [0005]    The catch member and resilient member are preferably formed integrally with the housing and may be moulded together from a plastics material. The resilient member may have an undulating shape. The coupling may include two resilient members extending between the catch member and the housing. The coupling preferably has two catch members on opposite sides of the housing.  
           [0006]    According to another aspect of the present invention there is provided an assembly of a corrugated pipe and a coupling according to the above one aspect of the invention mounted on an end of the pipe.  
           [0007]    A coupling for a conduit according to the present invention, will now be described, by way of example, with reference to the accompanying drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]    [0008]FIG. 1 is a sectional side elevation view of the coupling before assembly;  
         [0009]    [0009]FIG. 2 is a plan view of the coupling; and  
         [0010]    [0010]FIG. 3 is an enlarged sectional side elevation view of a part of the coupling.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]    The conduit  1  is entirely conventional and is of a rigid but bendable plastics material with a circular section and annular corrugations  10  on its external and internal surfaces. The right-hand end  11  of the conduit  1  is cut square.  
         [0012]    The coupling  2  has a housing  20  similar to previous housings, being a single-piece moulding of a rigid plastics material of substantially tubular shape. The housing  20  has a bore  22  extending axially along its length and divided into three portions, namely an entrance portion  23 , an intermediate portion  24  and an exit portion  25 . The entrance portion  23  at the left-hand end of the housing  20  has a constant diameter slightly greater than the external diameter of the conduit  1 . The intermediate portion  24  tapers along its length from a diameter at one end equal to that of the entrance portion  23  to a diameter at its opposite, right-hand end slightly smaller than the external diameter of the conduit  1 . The exit portion  25  has a reduced constant diameter and is separated from the intermediate portion  24  by an internal step  26 . Towards its left-hand end, the housing  20  is formed with retaining means in the form of two locking arms or catches  27  and  28  within respective square apertures  29  and  30  in the wall of the housing  20 . The left-hand end of each arm  27  and  28  is attached with the housing  20  by a hinge portion  31  of reduced thickness at the left-hand side of the apertures  29  and  30 , which enables the arms to be flexed resiliently outwardly and inwardly. Each arm  27  and  28  has an inwardly-extending tooth  32  at its free, right-hand end. The coupling could have any number of one or more locking arms. The natural position of the locking arms  27  and  28  is extending slightly inwardly, as shown in FIGS. 1 and 3. The opposite end  33  of each arm  27  and  28  is linked with the housing  20  by means of two narrow, thin webs or tabs  34  and  35  spaced from one another across the width of the arms. Viewed in elevation, the tabs  34  and  35  have a wavy, undulating shape so that length of the tabs is greater than the distance they span between the arms  27  and  28  and the edge of the aperture  29  or  30 . The tabs  34  and  35  are moulded integrally with the housing  20  and the arms  27  and  28  as a single piece. The shape, thickness and material of the tabs  34  and  35  make them flexible and resilient.  
         [0013]    The outside of the housing  20  has flats  42  in the region of the intermediate portion  24  to enable the housing to be gripped by a spanner. The forward, right-hand end of the housing  20  has an external screw thread  43  by which the coupling  2  can be screwed into a cooperating female coupling (not shown). Instead of a screw thread, the housing could have other forms of fixing formation, such as barbs or spring catches.  
         [0014]    In use, the coupling  2  is provided as a single component. The user simply pushes the forward end  11  of the conduit  1  into the rear end of the housing  20  so that the arms  27  and  28  flex outwardly slightly as their teeth  32  ride over corrugations  10 . As this happens, the tabs  34  and  35  flex outwardly and stretch slightly by flattening their undulations. Rearward movement of the conduit  1  is prevented by the locking arms  27  and  28 , which engage the conduit  1  more tightly as a withdrawing force is applied.  
         [0015]    If the conduit  1  should be inserted incorrectly so that the teeth  32  on the arms  27  and  28  sit on a corrugation  10  instead of between corrugations, the hinge portion  31  will be stressed by prolonged deformation and may take a set in the outwardly deformed position so that it only applies a reduced force urging the arms inwardly. However, the tabs  34  and  35  also apply an inward force to the free end of the arms  27  and  28 , the shape of the tabs making them more flexible than the hinge  31  and less prone to taking a set in the extended position. Thus, if the conduit  1  should be pulled back after a prolonged period of incorrect insertion, the force applied by the tabs  34  and  35  will be sufficient to bring the arms  27  and  28  back in. Their teeth  32  will then lock in a groove between corrugations  10  and retain the conduit  1  securely within the coupling  2 . After a period of time in this locking position, the hinge  31  will recover the major part of its initial properties. The tabs  34  and  35  also have the effect of resisting excessive inward force on the retaining arms  27  and  28  of the kind that might be produced if severe tensile force is applied to pull the conduit  1  out of the coupling  2 .  
         [0016]    The coupling can be a single-piece, integral component, thereby keeping manufacturing costs low and avoiding the risk of lost parts.