Abstract:
A pipe fitting with a body adapted for connection at a first end thereof to a supply pipe and at a second end thereof to a distribution pipe so as to permit fluid communication between the supply pipe and the distribution pipe. The body is provided with first valve device by which said fluid communication can be interrupted. The body is provided with an upstream port and a downstream port, respectively upstream and downstream, in use, of the first valve device. The upstream port and said downstream port permitting the first valve device to be by-passed and fluid from the supply pipe to be introduced to the distribution pipe.

Description:
FIELD OF THE INVENTION 
   This invention relates to a pipe fitting, and in particular but not exclusively to a pipe fitting of utility in the connection of a new water main to a public potable water distribution system. 
   BACKGROUND 
   Whenever a new water main is laid, for example to service a new housing development, it must be cleaned out and sterilised prior to connection to the existing mains, and also pressure-tested. The procedures involved are governed by stringent regulations. 
   In the United Kingdom the responsible authority is the Drinking Water Inspectorate (DWI). All methods currently approved by the DWI require two separate visits to site to carry out pipe fitting operations. DWI requires the positive isolation of new mains until they have successfully passed a bacteriological test after sterilisation. 
   One known method of satisfying DWI regulations is illustrated in  FIG. 1 . In this method, a flanged T-piece connector  1  is installed in the existing main  2 . The side arm of the T-piece  1  is connected to a sluice valve  3 . Temporary works comprising a further flanged T-piece  4  and a flanged spigot  5  are installed between the sluice valve  3  and the new main  6 . To achieve the desired isolation, however, a steel plate  7  (known as a “spade”) is interposed between the sluice valve  3  and the new main  6 . The side arm of the second T-piece  4  is connected via a sluice valve  8  to a fire hydrant  9 . The fire hydrant  9  is connected via a temporary by-pass-pipe  10  to a tapping  11  on the existing main  2 . The by-pass pipe  10  is fitted with a double non-return check valve  12 , an injection point  13  for sterilant and a meter  14 . 
   The arrangement shown in  FIG. 1  suffers from numerous disadvantages. First, the formation of the mains tapping  11  on the existing main  2  is problematic. It involves working on the main  2  while the main is under pressure and this carries a certain safety risk. If any problems occur when the tapping  11  is being made, the necessary remedial action may involve considerable interruption to the supply carried by the existing main  2 . Secondly, after the new main  6  has been successfully connected to the existing supply, the temporary works (second T-piece  4 , fire hydrant  9  etc) are generally discarded. This is wasteful and expensive. 
   Another standard method of commissioning a new main is illustrated in  FIG. 2 . In this case, the T-piece  21  installed in the existing main  22  is connected via a sluice valve  28  to a first fire hydrant  23 , and the end of the new main  24  is connected to a second fire hydrant  25 . The two hydrants  23 , 25  are connected by a temporary by-pass pipe  26 , as in the first method. The two hydrants  23 , 25  are braced apart by telescopic struts  27 . While this method does not involve any live operations on the existing main  22 , it still involves the installation of temporary works which are generally subsequently discarded. 
   The most fundamental problem with both the methods described above, however, and with variations on those methods that are also commonly used, is that connection of the new main to the existing supply after sterilisation necessarily involves removal of at least some of the temporary components so that the steel spade (first method) or one or both hydrants (second method) can be removed. Thus, after the new main has been sterilised it is once again exposed to the environment, leading to a risk of chemical or bacteriological contamination. It is precisely that risk that the regulations governing the procedure are intended to eliminate. 
   SUMMARY 
   There has now been devised a pipe fitting and a method of utilisation thereof which overcomes or substantially mitigates the above-mentioned or other disadvantages of the prior art. 
   According to a first aspect of the invention, there is provided a pipe fitting comprising
         a body adapted for connection at a first end thereof to a supply pipe and at a second end thereof to a distribution pipe so as to permit fluid communication between the supply pipe and the distribution pipe, the body being provided with first valve means by which said fluid communication can be interrupted, and the body being provided with an upstream port and a downstream port, respectively upstream and downstream, in use, of said first valve means, said upstream port and said downstream port permitting the first valve means to be by-passed and fluid from the supply pipe to be introduced to the distribution pipe.       

   Where the pipe fitting is used in the commissioning of a new potable water main, that new main constitutes the distribution pipe and the supply pipe is an existing main to which the new main is connected. In general, as used herein, the term “supply pipe” denotes a pipe upstream of the pipe fitting from which, in use, fluid flows to the pipe fitting and “distribution pipe” denotes a pipe downstream of the pipe fitting by which fluid flows away from the pipe fitting. 
   The pipe fitting according to the invention is advantageous primarily in that the first valve means effectively isolates the new main from the existing water supply during commissioning of the new main, yet the first valve means can be opened after the new main has been sterilised without exposing the new main to the environment. A particularly important benefit of the use of the pipe fitting according to the invention is that it enables complete sterilisation of a new water supply main. This is in contrast to current methods of commissioning new water mains which necessarily result in certain lengths, sometimes 10 m or more, not being sterilised at all. Use of the pipe fitting also substantially eliminates the need for temporary works and the associated waste of resources. Furthermore, the first valve means may readily be opened at any time subsequent to commissioning of the new main to temporarily interrupt water flow along the new main, for instance to enable maintenance or repair work to be carried out. 
   The first valve means may take the form of a closure plate adapted to be received within the body of the pipe fitting. 
   The closure plate may be of any material having suitable toughness and durability to withstand the pressures to which it will be exposed during use. Most preferably, the closure plate is of a suitable metal, eg steel. 
   The closure plate is most preferably engageable with the body of the pipe fitting with a sliding action. The closure plate most preferably slides in a slot formed in the body of the fitting, most preferably transverse to the longitudinal axis of the pipe fitting. Suitable seals, eg of an elastomeric material such as neoprene, are preferably provided around the periphery of the slot and/or the periphery of the closure plate to prevent leakage of water or other fluid past the closure plate. 
   The closure plate may be completely removable from the pipe fitting, the seals around the slot serving to close and seal the slot when the closure plate is so removed. Once the closure plate has been removed in this way, a suitable capping member may be applied to the pipe fitting to completely and securely close the slot and prevent escape of water under pressure from within the pipe fitting. In such a case, the first valve means may constitute a valve of the “spade” type. 
   In other embodiments, the closure plate may not be completely removable but may instead be retractable from its operative position, in which flow of fluid through the pipe fitting is interrupted, into a recess or enclosure forming part of the pipe fitting. 
   To facilitate sliding movement of the closure plate, the closure plate is preferably formed with suitable means for engagement by the operator. Where the closure plate extends externally of the pipe fitting, such means may simply comprise formations by which the closure plate may be grasped manually by the operator so as to be drawn out of the pipe fitting or pressed into the pipe fitting. More preferably, however, there are also provided means by which the closure plate may be acted upon by mechanical means effective to slide the closure plate into or out of the pipe fitting. Such mechanical means may, for instance, comprise jacking means having a threaded spindle by rotation of which the closure plate may be moved. Conveniently, a spigot is mounted on the spindle so that rotation of the spindle causes the spigot to move relative to the foot of the jacking means. If the spigot is engaged in the closure plate, rotation of the spindle thus causes the closure plate to be drawn in or out of the pipe fitting. The advantage of the use of such a jacking means is primarily that it enables the closure plate to be moved in a controlled manner which, for instance, reduces the risk of the new main being exposed to sudden increases in pressure. 
   Where the closure plate is retained and accommodated within the pipe fitting, it is preferably linked to an actuating mechanism that is operable from the exterior of the pipe fitting. The closure plate may, for instance, be mounted on a threaded spindle which projects from the pipe fitting and by rotation of which the closure plate may be raised or lowered. A particularly preferred form of such a closure plate constitutes a valve of the “resilient-seat” type, in which the closure plate has a coat of a resilient, commonly elastomeric, material. 
   The upstream and downstream ports are preferably aligned symmetrically on either side of the closure plate. Since the pipe fitting will most commonly be fitted below ground level, it is convenient for the upstream and downstream ports to be readily accessible from above. This is most readily achieved if the ports open upwardly in use. However, it is preferred, at least for the downstream port, for the ports to open into the interior of the pipe fitting horizontally, the outlet of the downstream port most preferably being aligned with the centre of the pipe fitting. This may be a regulatory requirement, since such an arrangement optimises the mixing and distribution of sterilant introduced via the downstream port into the flow of, for example, water through the pipe fitting. 
   The upstream and downstream ports are preferably fitted, in use, with suitable valves, the valves also being adapted for connection to the ends of a temporary by-pass pipe similar to that used in the prior art methods described above. The upstream and downstream ports are preferably capable of being closed off, so that the valves can be removed once the new main is fully commissioned. To this end, the ports are preferably adapted to receive closure caps which can preferably be fitted through the valves using an “under-pressure” tool of a type which is known per se. 
   As in the prior art, temporary connection between the existing main and the isolated new main is achieved by means of a by-pass pipe which in the case of the invention extends from the upstream port to the downstream port. As in the prior art, the by-pass pipe will generally be fitted with at least one, and more preferably two, non-return check valves to prevent flow of water from the new main to the existing main. The by-pass pipe will generally also be fitted with a flow meter and, downstream of the non-return valve(s) also with an injection point for sterilant. 
   Thus, according to a second aspect of the invention, there is provided a pipe assembly comprising a supply pipe and a distribution pipe, and a pipe fitting interposed therebetween, said pipe fitting comprising
         a body connected at a first end thereof to the supply pipe and at a second end thereof to the distribution pipe so as to permit water to flow from the supply pipe to the distribution pipe, the body being provided with first valve means by which said flow can be interrupted, and the body being provided with an upstream port and a downstream port, respectively upstream and downstream, in use, of said first valve means, said upstream port and said downstream port permitting the first valve means to be by-passed and water from the supply pipe to flow via a by-pass pipe connected to the upstream and downstream ports to the distribution pipe.       

   As described above, the supply pipe may be an existing potable water main and the distribution pipe a new main connected to the existing main. 
   Although the first valve means may in many cases be adequate to achieve complete and satisfactory isolation and separation of the new main from the existing main, in order to further ensure that the isolation is complete a second valve means may be provided, the first and second valve means being spaced apart on the longitudinal axis of the pipe fitting. 
   In such a case, the upstream port is, in use, upstream and the downstream port is downstream of both first and second valve means. 
   Preferably, both first and second valve means comprise a closure plate adapted to be received within the body of the pipe fitting. Where two closure plates are provided, in the event of leakage of water past either of the closure plates, such water will accumulate in the space between the closure plates and will not be forced under pressure past the other. The space between the closure plates may be provided with an outlet by which any such accumulated water may be drained or pumped off. If the space between the two closure plates is vented then that space will be at lower pressure than both the new and existing mains, thereby ensuring that any leakage past either closure plate is into that space and not into either main. 
   Where the pipe fitting includes both first and second valve means, it is preferred that at least one of the valve means is of a design suitable for closing off dynamic flow of fluid through the pipe fitting. Where the bore of the pipe fitting is relatively small and/or where the fluid flows at relatively low pressure, simple spade-type valves may be suitable. In other applications, however, a valve having a more robust closure plate, with mechanical actuation, may be preferable. It is particularly preferred to utilise a gate valve comprising a robust closure plate driven by rotation of a threaded spindle, the closure plate being mounted on the spindle such that rotation of the spindle causes the closure plate to be raised or lowered. A particularly preferred form of such a valve is a resilient-seat valve, in which the closure plate has a coat of a resilient, commonly elastomeric, material. 
   Where the pipe fitting incorporates both a spade-type valve and a resilient-seat valve or similar, the pipe fitting is preferably installed with the latter valve upstream of the former. 
   The applications in which the pipe fitting according to the invention is of particular utility will generally involve pipes with bores of the order of several tens of millimetres and greater. Typically, the pipes will have bores greater than 50 mm, eg 80 mm, 100 mm or 120 mm. For most applications, the bore will not be greater than several hundred millimetres, eg 600 mm or less, more commonly less than 250 mm. Most commonly, the pipe fitting will have an internal bore that matches the bore or internal diameter of the pipes to which it is fitted. 
   According to a further aspect of the invention, there is provided a method of connecting a new water main to an existing water main, which method comprises the steps of
     a) installing between the existing main and the new main a pipe fitting provided with first valve means movable from an open position in which the existing main and the new main are in communication, to a closed position in which water flow from the existing main to the new main is interrupted;   b) forming a temporary conduit from an upstream port in said body to a downstream port in said body, said temporary conduit containing unidirectional valve means and means for injecting a sterilant into said temporary conduit;   c) with first valve means in the closed position, flushing the new main with water from the existing main via the temporary conduit;   d) closing off and removing the temporary conduit; and   e) moving the first valve means to the open position.   

   Although described herein primarily with reference to the commissioning of a new potable water main, the pipe fitting according to the invention may be useful in many other applications, including foul water or sewerage applications. The pipe fitting may be of utility as a replacement or substitute for conventional valves. 
   It will also be appreciated that the pipe fitting according to the invention may be incorporated into components of various forms, eg T-pieces or the like. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which 
       FIG. 1  is a schematic plan view of a first conventional arrangement for connection of a new water main to an existing potable water main; 
       FIG. 2  is a view similar to  FIG. 1  of a second conventional arrangement; 
       FIG. 3  is a side view of a first embodiment of a pipe fitting according to the invention; 
       FIG. 4  is a plan view of the pipe fitting of  FIG. 3 ; 
       FIG. 5  is an end view of the pipe fitting of  FIGS. 3 and 4 ; 
       FIG. 6  is a sectional view on the line VI—VI in  FIG. 3 ; 
       FIG. 7  is a sectional side view of the pipe fitting of  FIG. 3  with a closure plate in a closed position and a jack fitted; 
       FIG. 8  is a view similar to  FIG. 7  but with the closure plate raised to an open position; 
       FIG. 9  shows a closure plate used in the pipe fitting of  FIGS. 3 to 8 ; 
       FIG. 10  is a view similar to  FIGS. 1 and 2  of the pipe fitting of  FIGS. 3 to 8  in use; 
       FIG. 11  is a view similar to  FIG. 7  of a second embodiment of a pipe fitting according to the invention; 
       FIG. 12  is a view similar to  FIG. 10  of the embodiment of  FIG. 11 , in use; and 
       FIG. 13  is a sectional side view of a third embodiment of a pipe fitting according to the invention. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 and 2  illustrate known methods for isolating a new water main from an existing public potable water main, and have been described above. 
     FIGS. 3 to 8  illustrate a first embodiment of a pipe fitting (generally designated  31 ) according to the invention and  FIG. 10  illustrates the manner in which the pipe fitting  31  is used. 
   Referring first to  FIG. 3 , the pipe fitting  31  is cast or otherwise formed as a unitary component inductile iron or other suitable material. It comprises a body  32  of generally tubular form, the body  32  having at each end thereof an annular flange  33 , 34  for attachment to adjacent components. The flanges  33 , 34  are formed with spaced apart holes  35  (see  FIG. 5 ) through which threaded bolts can be passed. 
   The central part  32   a  of the body  32  is enlarged relative to the rest of the body and receives in use a closure plate  36 , in a manner described more fully below. Ports  37 , 38  are provided at each side of the central part of the body  32 , between that part of the body  32  and the respective flanges  33 , 34 . 
   A plate  45  is bolted to the top of the enlarged central part of the body  32 . The plate  45  is formed with a slot  46  through which the closure plate  36  can be inserted, and with a cut-out  47  which serves for location of a jack, as described below. 
   The internal construction of the fitting  31  is shown in  FIGS. 6 to 8 . As can be seen in  FIGS. 7 and 8 , the fitting  31  has a circular bore  39  which is dimensioned appropriately for use of the fitting  31  with a particular diameter of mains pipe. In the enlarged central part  32   a  of the body  32  a slot  40  (aligned with the slot  46  in the plate  45 ) extends from the top of the fitting  31  into a peripheral annular groove  41  formed in the internal wall of the bore  39 . A pair of gaskets  42 , 43  (of neoprene or similar material) are fitted into that groove  41 . 
   The fitting  31  is used with the closure plate  36  which is shown in  FIG. 9 . The closure plate  36  comprises a flat steel plate  51  having a radiussed lower end, the radius corresponding to that of the groove  41 . The upper end of the closure plate  36  is formed with a moulded handle  53  having a central opening  54 . The closure plate  36  can be inserted via the slots  40  and  46  through the top of the fitting  31  and pressed downwards until its lower end seats in the groove  41 . In this condition the closure plate  36  is held between the gaskets  42 , 43  and separates one end of the fitting  31  from the other. 
   Referring once again to  FIGS. 7 and 8 , and also to  FIG. 6 , the ports  37 , 38  are formed in lateral extensions  64 , 65  formed on one side of the fitting  31 . The ports  37 , 38  open into the bore of the fitting  31  via respective openings  61 , 62 . As can be seen, the openings  61 , 62  are aligned with the longitudinal axis of the fitting  31 , and the terminal portions of the ports  37 , 38  are disposed horizontally. 
   As shown in  FIGS. 7 and 8 , the closure plate  36  can be raised or lowered by means of a jack  90 . With the closure plate  36  in the closed (lowered) position, as shown in  FIG. 7 , the jack  90  is engaged with the cut-out  47  in the plate  45 . Grooves (not visible in the drawings) in the foot of the jack  90  provide for positive engagement of the jack  90  with the plate  45 . The jack  90  comprises a pair of telescopic components  91 , 92 , the upper one of which  92  is mounted on a threaded spindle  93  such that rotation of the spindle  93  causes relative movement of the two components  91 , 92 . A spigot  94  extends from the upper component  92  through the opening  54  in the handle  53  of the closure plate  36 . Manual rotation of the spindle  93  thus causes the closure plate  36  to be raised to the open position shown in  FIG. 8 . Rotation of the spindle  93  in the other sense drives the closure plate  36  back to the  FIG. 7  position. 
   Manual raising and lowering of the closure plate  36  (ie without using the jack  90 ) will generally be possible, but use of the jack  90  enables far more controlled opening and closing of the pipe fitting  31 . 
   The manner in which the fitting of  FIGS. 3 to 8  is used will now be described, with reference to  FIG. 10 . The pipe fitting  31  is used in the connection of a new water main  71  to an existing public potable water main  72 . As with conventional methods of making such a connection, a T-piece connector  73  is first inserted in the existing main  72 , the side arm of the T-piece  73  being closed off by a sluice valve  74 . 
   The pipe fitting  31  is then interposed between the sluice valve  74  and the new main  71  and connected to both by means of double-flanged extension pipes  75 , 76 . An underground chamber  78  is built around the pipe fitting  31 . The ports  37 , 38  are fitted with 2″ (50 mm) gate valves which are connected together by temporary by-pass pipe  77  which is typically of 50 mm o.d. MDPE pipework with 1.5 inch nominal bore fittings. The pipe  77  is fitted with a double check valve assembly  79  and a check meter  80 . The pipe  77  is also fitted with a connection point  81  for chlorination and pressure testing of the new main  71 . The temporary by-pass pipe  77  may be several metres in length to provide for easy access and to facilitate the operations required during commissioning of the new main  71 . 
   Once the necessary components have been connected up as just described, and with the closure plate  36  pressed into the slot in the pipe fitting  31 , the sluice valve  74  can be opened. Flow of water from the existing main  72  to the new main  71  is prevented by the closure plate  36 . When the closure plate  36  is in this position, it may be locked in place by a padlock and chain or similar means, thereby preventing inadvertent or malicious removal of the closure plate  36  until commissioning of the new main  71  is complete. 
   The new main  71  may be flushed out by opening of the gate valves fitted to the ports  37 , 38 , thereby allowing water to flow along the bypass pipe  77 . The pressure of water introduced into the new main  71  in this manner may be used to flush out the new main  71 . This will normally be done by using the pressure of water to drive one or more cleansing swabs through the new main  71 . 
   Once the new main  71  is clean and has been emptied of water disinfection can be carried out. The new main  71  is filled once again with water from the existing main  72  and a disinfection chemical, most commonly sodium hypochlorite, is dosed into the by-pass pipe  77  via the injection point  81  and filling the new main  71  downstream of the check valves  79 . After a prescribed period the new main  71  is emptied and again filled with water from the existing main  72  through the by-pass pipe  77 . Samples of water are taken from the new main and sent to a laboratory for bacteriological analysis. Only when the results of the analysis show that disinfection has been satisfactorily achieved can the new main  71  be connected directly to the public potable water distribution system of which the existing main  72  forms part. 
   The closure plate  36  is unlocked and raised using the jack  90  and withdrawn fully from the slots  40 , 46 . The slot  46  can then be sealed by fitting of a capping plate and gasket (not shown) to the plate  45 . The plate  45  has four threaded bores  48 —see FIG.  4 —for this purpose. The gate valves fitted to the ports  37 , 38  are closed and the temporary by-pass pipe  77  is removed. The ports  37 , 38  can be closed off with caps applied through the gate valves using an under-pressure tool, in a manner known per se, and the gate valves removed. 
   Turning now to  FIGS. 11 and 12 , a second embodiment of a pipe fitting according to the invention is generally designated  131  and is of similar construction to the first embodiment  31 , save that its body  132  has two enlarged portions  132   a ,  132   b  which are identical in construction to the enlarged portion  32   a  of the first embodiment. Also, in addition to ports  161 , 162  which correspond in form and function to the ports  61 , 62  of the first embodiment, in this version of the pipe fitting, a further outlet port  163  is provided, between the two enlarged portions  132   a ,  132   b  of the body  132 . There is also provided a drainage point in the centre of the underside of the fitting  131 , which is fitted with a threaded plug  170 . 
   The manner of use of the second embodiment  131  is very similar to that of the first embodiment  31 . The difference is that in the case of the second embodiment  131 , the two ends of the fitting  131  are isolated not just by one closure plate but by two, each slidably engaged with slots in one of the enlarged body portions  132   a ,  132   b . This increases the security of the fitting, in that should water leak past one of the closure plates, eg from an existing live main under pressure, it does not contaminate the pipe at the other side of the other closure plate (eg a new main) but instead collects in the central space between the closure plates from where it can be pumped off via the additional port  163  or drained off by removal of the plug  170 . Because the central space is at lower pressure than either of the mains, any leakage takes place from the main into the central space, rather than vice versa. 
   A typical installation of the second embodiment  131  is illustrated in  FIG. 12 , which shows the fitting  131  connected at one end to a T-piece  151  installed in an existing water main  152  and at the other end to a double-flanged extension pipe  153  that may in turn be connected to a new main (not shown). 
   Turning now to  FIG. 13 , a third embodiment of a pipe fitting according to the invention is generally designated  231 . The body  232  of the pipe fitting  231  comprises two enlarged portions  232   a ,  232   b , and outlet ports  261 ,  262  which correspond in form and function to the ports  131 ,  132  of the second embodiment. There is also provided an outlet port  263 , corresponding in function to the outlet port  163  in the second embodiment, positioned in the underside of the body  232 . 
   Where the third embodiment  231  differs from the second embodiment  131  is that, instead of the enlarged portions  232   a ,  232   b  receiving identical closure plates of the form shown in  FIG. 9 , the second enlarged portion  232   b  houses a valve of the resilient-seat type in which a valve plate  276  is driven by a screw-threaded spindle  273 , as described below. 
   The first enlarged portion  232   a  of the body  232  extends above and below the central bore  239  of the body  232 . The first enlarged portion  232   a  is shaped in order to accept a closure plate of the form shown in  FIG. 9 . The upper section of the enlarged portion  232   a  also comprises solid horizontal extensions which extend in the longitudinal direction of the fitting  231 . 
   The upper part of the first enlarged portion  232   a  has a plate  245  bolted to the top, the bolts passing into the solid extensions. The plate  245  is formed with a vertical slot  246 , through which the closure plate can be inserted. The plate  247  is formed with integral upstanding lugs  247 , which provide means for fixing a jack (not shown) to the pipe fitting  231  in order to raise or lower the closure plate. A cover plate  248  is bolted to the plate  245  to seal the slot  246  in the plate  245 . 
   Within the upper section of the first enlarged portion  232   a , under the plate  245 , there is a closure plate guide  257  comprising a slot  258  which is aligned with the slot  246  in the plate  245 . Within the enlarged portion  232   a , adjacent to the periphery of the central bore  239  of the body  232 , there are two annular seal housings  255  of C-shaped cross-section. The seal housings  255  fit closely to the inside of the first enlarged portion  232   a  and the limbs of each seal housing  255  are aligned towards each other. 
   Within each seal housing  255  there is a main seal  251  which is encompassed almost completely by the limbs of the seal housing  255 . The main seals  251  are in contact with each other, the points of contact of the main seals  251  lying in the plane of the slots  246 ,  258 . In addition, there is a small rectangular recess in the outer side of each seal housing  255  within which there is a secondary seal  252 . In the lower section of the first enlarged portion  232   a , there is a drain port  253  beneath the seal housings  255  which is normally closed by a plug (not shown). Two plastic rings  259  are held in position by grooves in the interior wall of the central bore  239  and serve to hold the seal housings  255  in position. 
   The second enlarged portion  232   b  of the body  232  is of generally larger dimensions than the first enlarged portion  232   a . The second enlarged portion  232   b  includes an opening  270  leading vertically to an enclosure  275 . The enclosure  275  is closed on top by a dome  280  that is bolted onto the top of the second enlarged portion  232   b , a gasket  272  being interposed between the enclosure  275  and the dome  280 . 
   A spindle  273  is mounted axially for rotation within the enclosure  275 . A threaded drive ring  279  is mounted on the spindle  273  and is captivated within the enlarged upper part of a valve plate  276  such that rotation of the spindle  273  causes the drive ring  279  to travel along the spindle  273  and hence raises or lowers the valve plate  276 . The lower part of the valve plate  276  has a resilient coating  277  which extends upwards as far as the underside of the enlarged upper part of the valve plate  276 . 
   The dome  280  also comprises a ring  282  on its upper side which supports an annular gland  288  within the ring  282 . The gland  288  is formed with grooves in its interior surface and a groove in its external surface which contain sealing rings  284 ,  283 . The external sealing ring  283  presses against the interior surface of the ring  282 . 
   The spindle  273  extends vertically through an opening  289  in the dome  280 . The spindle  273  fits closely through the centre of the gland  288  and the sealing rings  284 . The spindle  273  further comprises a support ring  281  positioned between the gland  288  and the upper surface of the dome  280  which holds the spindle  273  in the correct vertical position. Bearings  287  between the support ring  281  and the gland  288  and between the support ring  281  and the upper surface of the dome  280  facilitate the rotation of the spindle  273 . 
   The upper end of the spindle  273  extends through the gland  288  and the a sealing ring  285  engaged with the gland  288 . A tapered dolly  286  is attached to the top of the spindle to receive a valve key (not shown). Turning of the valve key in one direction rotates the spindle  273 , which in turn raises the threaded drive nut  279 , which in turn raises the valve plate  276  into the enclosure  275 . Turning of the valve key in the other direction rotates the spindle  273  in the opposite direction, which in turn lowers the threaded drive nut  279 , which in turn lowers the valve plate  276  into engagement with the interior of the body  232 . 
   When the threaded drive ring  279  is in its lowest position, the resilient coating  277  on the lower side of the enlarged upper part of the valve plate  276  is pressed against the lower wall of the enclosure  275 , thereby sealing the enclosure  275  from the central bore  239 . In addition, the valve plate  276  is fully extended into the second enlarged portion  232   b  with the resilient coating  277  pressing against the interior walls of the second enlarged portion  232   b . The valve plate  276  and resilient coating  277  thereby prevent the flow of fluids along the central bore  239 . 
   A closure plate may also be inserted into the first enlarged portion  232   a  by removing the cover plate  248 . The closure plate is inserted, using a jack or otherwise, through the slots  246 ,  258  in the plate  245  and the plate guide  257  respectively and pressed downwards between the main seals  251  until the flow of fluid along the central bore  239  of the fitting  231  is prevented. The valve is opened by removing the closure plate, thereby allowing fluid flow along the central bore  239  of the fitting  231 . The slot  246  in the plate  245  is sealed by replacing the cover plate  248 . 
   The manner of use of the third embodiment  231  is very similar to that of the second embodiment  131 . The difference is that the third embodiment  231  includes a resilient seat valve which may be better suited to the interruption of dynamic fluid flow. Where the pipe fitting is installed in a live main under pressure and it is desired to interrupt the flow of water along that main, then the valve plate  276  is lowered by rotation of the spindle  273  until the resilient coating  277  seats against the internal surfaces of the body  232 . If necessary, a closure plate may then be inserted into the first enlarged portion  232   a.