The present invention relates to a method of modifying a hydrant, a hydrant bonnet assembly, a kit for use in modifying a hydrant, and to a hydrant. In particular, but not exclusively, the present invention relates to a method of modifying a hydrant of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant, to a hydrant bonnet assembly which may be suitable for use in a method of modifying such a hydrant, to a kit for use in modifying such a hydrant, and to a modified hydrant incorporating such a hydrant bonnet assembly.

In the water utilities industry, water is supplied under pressure through a water supply network. The network includes a system of pipes for transferring treated, potable water from a storage site to end users, which may be industrial and/or residential users. The arrangement of pipes used for transportation of the potable water to the end users is typically known as a "water mains distribution network".

The water mains usually includes a series of fire hydrants at regular locations along a length of the mains pipes, say at 150m to 300m spacings. These hydrants serve a number of functions including providing for connection of hoses to the water mains by the emergency fire service. Many different types of hydrants exist in different countries throughout the world, but all typically include a housing which is coupled to the water mains, an outlet to which the hoses may be coupled, and a valve for selectively opening the hydrant and thereby permitting water supply through the hoses.

In the United Kingdom, a large number of hydrants installed in the water mains network are of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant. The hydrant includes a body having an inlet which provides for fluid connection with the mains through a mains-tee, and a bonnet assembly mounted on the body. The bonnet assembly carries a valve known as a stopper which is threaded and rotated to thereby translate the stopper into and out of sealing abutment with a valve seat provided at the inlet, to control flow of fluid into the hydrant. The bonnet assembly also defines an outlet of the hydrant, which is spaced laterally from the inlet and provided in a side pocket or channel of the hydrant body. The hydrant throughbore extending between the inlet and the outlet is therefore highly deviated. A typical example of such a hydrant is the Series 29-288 Type 2 Underground Fire Hydrant PN 16 available from Aqua-Gas AVK Limited in the United Kingdom, which is manufactured according to British Standard BS750.

Equipment has been developed which can be inserted into the water mains through hydrants for carrying out inspection and/or repair functions. However, the ability of such equipment to be inserted through the deviated bores of such hydrants and past the valve stopper is restricted.

Also, in the event that the water mains suffers a breach and requires repair, it is necessary to shut off the mains at a primary control valve, a number of which are provided at intervals along branches of the mains. Typically, only a relatively small number of such primary valves are provided, compared to the number of hydrants. Closing one these primary valves presents a significant disruption, depriving a large number of end users of their supply of potable water. Furthermore, repairing the breach requires that the road or carriageway is excavated in the estimated region of the breach, causing disruption to traffic flow and presenting a hazard to health.

It is therefore amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a method of modifying a hydrant of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant to form a hydrant having a substantially straight throughbore, the method comprising the steps of: inserting a seal element into the hydrant through the outlet; actuating a valve of the hydrant to open the inlet; directing the seal element into the inlet and closing the inlet using the seal element; removing a bonnet assembly of the hydrant which carries the valve and which defines the hydrant outlet from a body of the hydrant which defines the hydrant inlet; and mounting a replacement bonnet assembly on the hydrant body, the replacement bonnet assembly defining an outlet of the hydrant which is arranged relative to the hydrant inlet so as to define a substantially straight throughbore extending between the inlet and the outlet.

In providing a method by which a hydrant having a deviated throughbore can be modified to include a substantially straight throughbore, the present invention enables enhanced access to a water main (or water 'mains') to which the hydrant is attached and without requiring replacement of the hydrant. For example, inspection equipment may be inserted through the substantially straight throughbore more easily than through the deviated throughbore, enabling precise location of, for example, a breach in the mains or regions of the mains requiring maintenance. Additionally, it may be possible to pass maintenance equipment down the substantially straight throughbore, for performing a maintenance procedure within the mains. The method of the present invention may allow such procedures without requiring shutting-off of the mains supply.

It will be understood that the term bonnet assembly used herein refers to an assembly for covering the hydrant, which is to be mounted on and thus coupled to the hydrant body. The bonnet assembly is typically provided, in use, uppermost of the hydrant, facilitating access to the interior of the hydrant (such as for maintenance) by removal of the bonnet assembly. The bonnet assembly may comprise a bonnet carrying the valve and an outlet element such as a tube defining the outlet to the hydrant, or the bonnet assembly may comprise a bonnet carrying the valve and itself defining the outlet.

The outlet of the replacement bonnet assembly may be arranged such that the outlet is aligned with the inlet when the replacement bonnet assembly is mounted on the hydrant body. The outlet may therefore be arranged on an axis of the inlet, and/or an axis of the outlet may be coaxial to an axis of the inlet.

The throughbore may be substantially straight in that an axis of the throughbore may extend between the inlet and the outlet substantially without, or entirely without, deviation. The method may comprise coupling a seal element deployment unit to the hydrant outlet, and then using the deployment unit to insert the seal element into the hydrant. The seal element deployment unit may be coupled to the hydrant outlet with the valve of the hydrant in a position where the inlet is closed. Accordingly, the deployment unit may be isolated from mains pressure during coupling to the hydrant body. The valve may then be actuated to open the inlet, exposing the deployment unit to the pressure of fluid in the hydrant (mains pressure). The seal element may then be inserted through the outlet and directed into the inlet.

The seal element may be directed through the inlet and located in a pipe such as a riser pipe coupled to the hydrant (which may be the case where the hydrant is coupled to a relatively deep mains). Accordingly, the seal element may be located outwith the hydrant.

The seal element may be directed into the inlet and located at least partly within the hydrant, such as at least partly within a bore of the hydrant body which bore defines the inlet (which may be the case where the hydrant is coupled to a relatively shallow mains). The seal element may be located entirely within the bore.

The method may comprise inserting a collapsible seal element into the hydrant, and may comprise inserting the collapsible seal element into the hydrant in a collapsed state. Following direction of the seal element into the inlet, the method may comprise actuating the seal element to move the element to an expanded state in which the seal element closes the inlet. Providing a collapsible seal element and inserting the element into the hydrant in a collapsed state may facilitate insertion of the seal element, passage of the element through the hydrant, and entry of the element into the inlet.

The method may comprise inserting an inflatable seal element into the hydrant and actuating the seal element to close the inlet by inflating the seal element. The method may comprise inserting an inflatable seal element in the form of an inflatable bag, and inflating the bag by supplying fluid under pressure to the bag, typically through a tube extending from the bag to the deployment unit. The method may comprise fixing or otherwise holding the seal element in the expanded state, optionally releasing the deployment unit from the hydrant, and then removing the bonnet assembly from the hydrant body. Where the seal element is inflatable, the method may comprise maintaining the fluid pressure in the element at the pressure required to expand the element and seal the inlet. Where the seal element is an inflatable bag, this may be achieved by closing a valve in the tube extending from the bag.

The method may comprise disconnecting the seal element from the deployment unit following closing of the inlet, to maintain the inlet closed and to facilitate removal of the bonnet assembly. The bonnet assembly may only be removed from the hydrant body following closing of the inlet, the seal element thereby isolating the hydrant from fluid at mains pressure.

The method may comprise reconnecting the seal element to the deployment unit following mounting of the replacement bonnet assembly on the hydrant body. This may facilitate recovery of the seal element, optionally collapse of the seal element, and reopening of the inlet.

The method may comprise mounting a replacement bonnet assembly on the hydrant body which has a valve arranged to control fluid flow through the outlet defined by the replacement bonnet assembly and thus flow through the hydrant. The method may comprise mounting a replacement bonnet assembly in the hydrant body which has a sliding gate valve for controlling fluid flow through the outlet, which sliding gate valve may be of the type utilised in the straight throughbore Freeflow Below Ground Hydrant available from E.Hawle Armaturenwerke GmbH in Austria. The Hawle hydrant includes a sliding gate-type valve for closing flow through the hydrant. It will be understood that the present invention offers advantages over the Hawle hydrant in that it would not be cost-effective to replace all deviated throughbore hydrants with such straight throughbore hydrants purely for the reason of providing the ability to enter the mains. Indeed, a typical deviated throughbore hydrant may last its entire operational lifetime without any requirement to enter the mains through the hydrant. Also, deviated hydrants function perfectly adequately in performing their primary functions, subject of course to wear and tear and deterioration over time, therefore replacement for the above purpose would generally not be cost-effective. Furthermore, replacing a hydrant typically requires excavation around the area of the hydrant, which is generally disruptive and undesired. Additionally, straight throughbore hydrants such as the Hawle hydrant are relatively large compared to deviated bore hydrants, and may not be suitable such as in the case of a relatively shallow mains. Finally, the valve equipment on hydrants such as the Hawle hydrant is typically found towards a lower end of the hydrant and built in. Thus access to the valve equipment for maintenance and/or replacement can be difficult, particularly in view of the size restrictions of conventional manholes, and the space available around the hydrant below ground. The method may comprise mounting a replacement bonnet assembly in the hydrant body which has an alternative type of valve. The valve may be a ball valve and may take the form of an eccentric plug valve.

The method may comprise arranging the replacement bonnet assembly such that it can mate with existing mountings or the like on the hydrant body. This may be achieved by providing the replacement bonnet assembly with a mounting arrangement corresponding to that on the bonnet assembly to be removed. For example, the bonnet assembly to be removed will typically comprise a number of bores shaped to receive fixings such as bolts, which bolts engage in corresponding threaded bores in the hydrant body to thereby secure the bonnet assembly to the body. Alternatively, the bonnet assembly to be removed may have a number of bores which align with unthreaded bores in a flange on the hydrant body, through which threaded bolts are located and secured using threaded nuts. In either case, the replacement bonnet assembly will typically be provided with corresponding bores, and may be provided with a plurality of bores arranged in a pattern corresponding to a pattern of bores in the bonnet assembly to be removed.

The method may comprise sealing the replacement bonnet assembly relative to the inlet of the hydrant, and may comprise mounting the replacement bonnet assembly on the hydrant body in sealing abutment with a valve seat defined by or provided at or adjacent to the inlet. The method may comprise locating a coupling tube of the bonnet assembly in sealing abutment with the valve seat. The tube may be secured against movement relative to the valve seat (following mounting of the replacement bonnet assembly on the valve body), or may be mounted for movement between a position out of sealing abutment with the valve seat and a position in sealing abutment.

The method may be a method of modifying a hydrant to facilitate access to a water main coupled to the hydrant through the modified hydrant. Accordingly, the method may be a method of accessing a water main through a hydrant coupled to the water main of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant. The method may comprise the step of inserting an inspection apparatus into the water main through the substantially straight throughbore of the replacement bonnet assembly. The method may comprise the step of carrying out a treatment activity on the water main. The treatment activity may comprise cleaning at least part of the water main, which may involve cleaning a pipe or pipes of the water main, and the step of cleaning the water main may comprise inserting an abrasive cleaning material into the water main and directing the cleaning material along a pipe or pipes of the water main to clean an internal surface of the pipe or pipes. The cleaning material may be ice, which offers the advantage that residual solids cleaning materials are left in the water main as the ice will melt after a period of time. It will be understood that other activities/treatments may be performed by accessing the water main through the hydrant throughbore.

According to a second aspect of the present invention, there is provided a method of accessing a water main through a hydrant coupled to the water main of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant, the method comprising the steps of: inserting a seal element into the hydrant through the outlet; actuating a valve of the hydrant to open the inlet; directing the seal element into the inlet and closing the inlet using the seal element; removing a bonnet assembly of the hydrant which carries the valve and which defines the hydrant outlet from a body of the hydrant which defines the hydrant inlet; mounting a replacement bonnet assembly on the hydrant body, the replacement bonnet assembly defining an outlet of the hydrant which is arranged relative to the hydrant inlet so as to define a substantially straight throughbore extending between the inlet and the outlet; and accessing the water main through the substantially straight throughbore. Further features and/or steps of the method of the second aspect of the present invention are defined above in relation to the first aspect.

According to a third aspect of the present invention, there is provided a retrofit bonnet assembly for a hydrant of a type having a deviated throughbore extending between an inlet of the hydrant and an outlet of the hydrant, for modifying the hydrant to include a substantially straight throughbore; wherein the retrofit bonnet assembly is adapted to be mounted on a body of the hydrant, which body defines the inlet; and wherein the retrofit bonnet assembly defines an outlet which, when the retrofit bonnet assembly is mounted on the body of the hydrant, is arranged such that a throughbore extending between the inlet and the outlet is substantially straight.

The retrofit or replacement bonnet assembly may take the form of the replacement bonnet assembly defined above in relation to the first aspect of the present invention.

The retrofit bonnet assembly may be arranged such that the outlet of the replacement bonnet assembly is aligned with the inlet when the retrofit bonnet assembly is mounted on the hydrant body. The outlet may therefore be arranged on an axis of the inlet and/or an axis of the outlet may be coaxial to an axis of the inlet. The throughbore may be substantially straight in that an axis of the throughbore may extend between the inlet and the outlet substantially without, or entirely without, deviation.

The retrofit bonnet assembly may comprise a valve arranged to control fluid flow through the outlet and thus flow through the hydrant. The bonnet assembly may comprise a sliding gate valve for controlling fluid flow through the outlet, which sliding gate valve may be of the type utilised in the straight throughbore Freeflow Below Ground Hydrant available from E.Hawle Armaturenwerke GmbH in Austria.

The retrofit bonnet assembly may be adapted to mate with existing mountings or the like on the hydrant body. This may be achieved by providing the retrofit bonnet assembly with a mounting arrangement corresponding to that of a bonnet assembly to be replaced For example, the bonnet assembly to be removed will typically compose a number of bores shaped to receive fixings such as bolts, which bolts engage in corresponding threaded bores in the hydrant body to thereby secure the bonnet assembly to the body Alternatively, the bonnet assembly to be removed may have a number of bores which align with unthreaded bores m a flange on the hydrant body, through which threaded bolts are located and secured using threaded nuts In either case, the retrofit bonnet assembly will typically be provided with corresponding bores, and may be provided with a plurality of bores arranged m a pattern corresponding to a pattern of bores in the bonnet assembly to be replaced

The retrofit bonnet assembly may be arranged to be mounted on a portion of the body which is located uppermost, in use, of the hydrant Thus the bonnet assembly may be arranged to form a cap or the like of the hydrant body

The retrofit bonnet assembly may be adapted to be sealed lelative to the inlet of the hydrant, and be adapted to be mounted on the hydrant body in sealing abutment with a valve seat defined by or provided at or adjacent to the inlet The retrofit bonnet assembly may compose a coupling tube or the like extending from the bonnet assembly for location in sealing abutment with the valve seat The tube may be adapted to be secured against movement relative to the valve seat (following mounting of the replacement bonnet assembly on the valve body) and thus mounted to and secured against movement relative to a main part of the ietiofit bonnet assembly, or may be moveable between a position out of sealing abutment with the valve seat and a position in sealing abutment and thus may be moveable relative to said bonnet assembly mam part

According to a fourth aspect of the present invention, there is provided a kit for use in modifying a hydrant of a type having a deviated thioughbore extending between an inlet defined by a body of the hydrant and an outlet defined by a bonnet assembly of the hydrant mounted on the body, to form a hydrant having a substantially stiaight throughbore, the kit comprising a seal element for closing the inlet to facilitate removal of the existing bonnet assembly, the seal element adapted to be inserted into the hydiant through the outlet defined by the existing bonnet assembly, and a retrofit bonnet assembly adapted to be mounted on the body following removal of the existing bonnet assembly, the retrofit bonnet assembly defining a new outlet which, when the retrofit bonnet assembly is mounted on the body of the hydrant, is arranged such that a throughbore extending between the inlet and the outlet is substantially straight.

The outlet of the retrofit bonnet assembly may be aligned with the inlet when the bonnet assembly is mounted on the hydrant body. The outlet may therefore be arranged on an axis of the inlet and/or an axis of the outlet may be coaxial to an axis of the inlet. The throughbore may be substantially straight in that an axis of the throughbore may extend between the inlet and the outlet substantially without, or entirely without, deviation.

The kit may further comprise a seal element deployment unit adapted to be coupled to the outlet of the existing bonnet assembly, for inserting the seal element into the hydrant. The seal element deployment unit may be adapted to be coupled to the hydrant outlet with a valve of the hydrant in a position where the inlet is closed.

The seal element may be a collapsible seal element, and may be adapted to be inserted into the hydrant in a collapsed state. The seal element may be actuable to move to an expanded state in which the seal element closes the inlet.

The seal element may be an inflatable seal element, and may be actuable to close the inlet by inflation of the seal element. The seal element may be an inflatable bag and may be adapted to be inflated by applied fluid pressure, through a tube or the like extending from the bag to the deployment unit.

The seal element may comprise a valve or the like which may allow the seal element to be fixed or otherwise held in the expanded state.

The seal element may be disconnectable from the deployment unit following closing of the inlet, to maintain the inlet closed and to facilitate removal of the existing bonnet assembly. The seal element may be reconnectable to the deployment unit following mounting of the retrofit bonnet assembly on the hydrant body. The retrofit bonnet assembly may comprise a valve arranged to control fluid flow through the outlet defined by the bonnet assembly and thus flow through the hydrant. The bonnet assembly may comprise a sliding gate valve for controlling fluid flow through the outlet, which sliding gate valve may be of the type utilised in the straight throughbore Freeflow Below Ground Hydrant available from E.Hawle Armaturenwerke GmbH in Austria.

According to a fifth aspect of the present invention, there is provided a deviated throughbore hydrant modified to include a straight throughbore, the modified hydrant comprising: a body defining an inlet to the hydrant; a retrofit bonnet assembly mounted on the body of the hydrant and which defines an outlet of the hydrant; wherein the outlet of the hydrant defined by the retrofit bonnet assembly is arranged such that a throughbore extending between the inlet and the outlet is substantially straight.

Preferably, the retrofit bonnet assembly takes the form of the retrofit bonnet assembly defined above.

The body may comprise a side pocket or channel adjacent to a portion defining the inlet, and a valve mechanism (or part thereof) of the retrofit bonnet assembly may be mounted on or in said side pocket.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a partial cross-sectional side view of a deviated bore hydrant of a type to which the method of the present invention may be applied, the hydrant shown in use, coupled to a water main; Figure 2 is a view of the hydrant of Figure 1 at a stage in a method of modifying the hydrant to form a hydrant having a substantially straight throughbore according to the present invention;

Figure 3 is a view of the hydrant of Figure 1 following modification to form a hydrant having a substantially straight throughbore, and of a retrofit bonnet assembly for a hydrant, in accordance with an embodiment of the present invention; and

Figures 4 to 1 1 are views of the hydrant of Figure 1, taken from the opposite side, and illustrating steps in the method of modifying the hydrant according to the present invention.

Turning firstly to Figure 1 , there is shown a hydrant of a type to which the method of the present invention may be applied, the hydrant indicated generally by reference numeral 10. The hydrant 10 is shown connected to a water main 12 through a riser tee 14 and riser pipe 16. Typically, the water main 12 will be located below ground level, and the riser pipe 16 will extend up through the ground into a chamber (not shown) in which the hydrant 10 is located, access to the hydrant 10 being provided through a suitable manhole at road or pavement/sidewalk surface level. As will be understood by persons skilled in the art, the hydrant 10 may alternatively be coupled directly to the riser tee 14, such as in a situation where the main 12 is relatively shallow.

The hydrant 10 is of a type including a body 18 having an inlet 20 which provides for fluid communication with the main 12 through the riser pipe 16 and riser tee 14. The hydrant 10 also includes a bonnet assembly 22 mounted on the body 18, and which carries a valve in the form of a stopper 24. The stopper 24 includes a shaft 26 having an enlarged threaded portion 28 which engages a corresponding threaded section 30 on an arm or spider 32 formed in the body 18. In this fashion, rotation of the stopper 24 advances and retracts the stopper towards and away from a valve seat 34 adjacent to the inlet 20. This enables closing of the inlet 20 by movement of a body seat 36 of the stopper 24 into sealing abutment with the valve seat 34. The stopper 24 is shown in the closed position in Figure 1 , abutting the valve seat 34. The bonnet assembly 22 also includes an outlet 38, defined by an outlet tube 39 which is threaded and carries a dust cap 40. In use and when it is desired to draw water from the main 12 through the hydrant 10, the dust cap 40 is first removed, and a hose or the like coupled to the outlet 39. A stem cap 42 on the stopper shaft 26 is then rotated using a valve key or handle 44, to retract the body seat 36 away from the valve seat 34, thereby opening the inlet 20. This then permits fluid flow up from the main 12, through the inlet 20 into the body 18, and out of the hydrant through the outlet 38.

It will be understood from the foregoing and from Figure 1 that the hydrant 10 defines a deviated throughbore extending between the inlet 20 and the outlet 38.

In an embodiment of the present invention, a method of modifying a hydrant of the type shown in Figure 1, to form a hydrant having a substantially straight throughbore, is provided.

In general terms, and referring also to Figures 2 and 3, which show the hydrant 10 of Figure 1 at a stage during modification and following modification to form a hydrant having a substantially straight throughbore, the method of the present invention generally comprises the following steps.

With the stopper 24 of the hydrant 10 in the closed position shown in Figure 1 , a seal element 46 is inserted into the hydrant 10 through the outlet 38. The stopper 24 is then actuated to open the inlet 20, and the seal element 46 is directed into the inlet 20 and used to close the inlet. The seal element 46 is shown in Figure 2 in a position closing the inlet 20. It will be appreciated that, whilst the stopper 24 is shown in Figure 2 in the closed position, the stopper will actually be in an open position permitting passage of the seal element 46 into the inlet 20.

The bonnet assembly 22 is then removed from the body 18 and a replacement or retrofit bonnet assembly 48 is mounted on the body 18. The replacement bonnet assembly 48 defines an outlet 50 of the modified hydrant, the modified hydrant now indicated by reference numeral 10'. The replacement bonnet assembly 48 is shaped such that the outlet 50 is aligned with the hydrant inlet 20, to define a substantially straight throughbore extending between the inlet and the outlet. Modification of the hydrant 10 to form the hydrant 10' including the replacement bonnet assembly 48 and in which the hydrant 10' has a substantially straight throughbore offers numerous advantages in use of the hydrant. In particular, improved access to the main 12 is permitted through the hydrant 10' in comparison to the hydrant 10. For example, inspection and repair apparatus may be more easily inserted through the hydrant 10' and into the main 12. In particular, certain types of inspection apparatus include a camera (not shown) mounted on a cable which may be manipulated for passage from the riser tee 14 into the main 12, in a similar fashion to a medical endoscope. Modifying the hydrant 10 to include a substantially straight throughbore greatly assists in insertion of the camera, and passage of the camera along the main 12.

Furthermore, the method of the present invention permits modification of the hydrant 10 to include a substantially straight throughbore without requiring excavation of the site in the region of the hydrant 10. This is because the bonnet assembly 22 can be easily accessed through the manhole for removal and replacement with the bonnet assembly 48.

The method and apparatus of the present invention will now be described in more detail, with reference also to Figures 4 to 1 1, which illustrate further steps in the method of modifying the hydrant 10. Each of Figures 4 to 11 show the hydrant 10 and riser pipe 16 in partial longitudinal section, for illustrative purposes, and are taken from the opposite side to the views of Figures 1 to 3.

With the hydrant 10 in the closed state of Figure 1, the outlet tube 39 of the bonnet assembly 22 is first released from the hydrant body 18. This is achieved by releasing locking bolts extending through bores (not shown) in a flange 52 of the outlet tube 39, two of which are shown and given the reference numeral 54. The bolts 54 are threaded and engage in corresponding threaded bores (not shown) in the hydrant body 18. Following removal of the outlet tube 39, a deployment unit 56 for the seal element 46 is secured to the hydrant body 18. It should be noted at this stage that two options exist for securing the deployment unit 56 to the hydrant body 18, one of which is shown in Figure 2, and the other of which is shown in Figures 4 to 1 1. In the first option, the deployment unit 56, which is shown only schematically in Figure 2, is coupled to the outlet tube 39 of the bonnet assembly 22, and thus the outlet tube 39 remains in place on the hydrant body 18 for the time-being. In the second option, the deployment unit 56 carries a flange 58 by which the unit is secured to the hydrant body 18. It is this second option which will be described in detail herein.

Accordingly, following securing of the deployment unit 56 to the body 18 using bolts which engage in the corresponding bores for securing the outlet tube 39, the unit 56 is coupled and sealed relative to the hydrant body 18. The seal element 46 takes the form of an inflatable bag connected through the deployment unit 56 to a source of pressurised fluid (not shown), such as a water pump, using a tube 59. The bag 46 will be shown and described in the collapsed state below.

Following coupling of the deployment unit 56 to the body 18, the stopper 24 is actuated to move to the open position, as shown in Figure 5. The deployment unit 56 is then exposed to water at mains pressure, which is contained via a suitable sealing arrangement 60 around the tube 59. The deployment unit includes a body 62 which houses the collapsed bag 46 and through which the bag may slide for passage into the hydrant 10. The deployment unit 56 also includes a curved guide tube 64 having an outlet 66 which is positioned near the hydrant inlet 20, to facilitate direction of the bag 46 into the inlet. Figure 6 shows the bag 46 emerging from the outlet 66 and entering the inlet 20.

Further sliding movement of the bag 46 relative to the body 62 and guide tube 64 moves the bag 46 down in to the riser pipe 16, as shown in Figure 7. The bag 46 is then inflated as shown in Figure 8, by supplying fluid into the bag along the tube 59 at a pressure greater than mains pressure. In practice, the pressure of fluid supplied to the bag 46 to inflate the bag will be significantly greater than mains pressure, to provide a sufficiently high pressure differential in order to maintain the position of the bag 46 within the riser pipe 16, and also to close flow into the hydrant 10. It will therefore be understood that, following inflation of the bag 46, the hydrant 10 is closed and isolated from mains pressure. A valve 76 in the tube 59 is then closed to maintain the applied pressure within the bag 46, and thus to hold the bag 46 in the inflated state shown in Figures 2 and 8. However, at this stage, fluid remaining in the hydrant 10 is at mains pressure, and this is vented before the next step in the method, by opening of a valve 68 shown schematically at Figure 2. Following venting, the remainder of the bonnet assembly 22, comprising the main bonnet 70, can be removed from the hydrant body 18 by releasing and removing threaded bolts, two of which are shown and given the reference numeral 72. It will be understood that the bolts 72 engage through bores (not shown) in a flange 74 of the main bonnet 70, and engage in corresponding threaded bores (not shown) in the hydrant body 18, in a similar fashion to the bolts 54. The hydrant 10 is shown following removal of the main bonnet 70 in Figure 9.

The deployment unit 56 can now be released from the bag 46 and removed from the hydrant body 18. Typically this is achieved by releasing the deployment unit 56 from the body 18 and then disconnecting the tube 59 from the bag 46 at a level above the valve 76 (Figure 2). Typically, a releasable coupling will be provided for connecting the portion of the tube 59 above the valve 76 to the valve, thereby permitting such release. The hydrant 10 is shown following removal of the deployment unit in Figure 10. The remaining portion of the tube 59 can now be fed back into the hydrant body 12 and directed up through an opening 78 which previously received the bonnet 22, as shown in Figure 11. The replacement bonnet assembly 48 (Figure 3) can then be secured to the hydrant body 18 to form the hydrant 10', having a straight throughbore. This is achieved by feeding the remaining portion of the tube 59 up through the outlet 50 defined by the outlet tube 51 , and then lowering the replacement bonnet assembly 48 on to the hydrant body 18. The bonnet assembly 48 includes a pattern of bores (not shown) arranged for receiving bolts corresponding to selected ones or indeed all of the bolts 54 and 72, and thus which bores align with the corresponding threaded bores in the hydrant body 18. Two of the bolts 72 are shown in Figure 3. The replacement bonnet assembly 48 can therefore be fitted to the hydrant body 18 without requiring any modification to the body itself.

The replacement bonnet assembly 48 includes a valve in the form of a sliding gate valve 80 of a type manufactured by Hawle Armaturenwerke GmbH of Austria, and found in their commercially available straight throughbore Freeflow Below Ground Hydrant. The sliding gate valve 80 includes a valve stem 82 which is coupled to an actuator plate 84 and rotated by a handle 86. The bonnet assembly 48 includes a lower housing 88 and an upper housing 90 which are coupled together and sealed using appropriate seals such as O-rings. An end 92 of a shaft 94 of the valve stem 82 is rotatably mounted in the lower housing 88, and the stem extends up through the upper housing 90. A dog or key 96 is provided on the actuator plate 84, and is moveable within an arcuate channel 98 in the lower housing 88, ends of the channel defining stops for restricting movement of the dog 96 and thus of the actuator plate. A sliding gate 100 is coupled to the actuator plate 84 and, upon rotation of the handle 86, is moved between the extents of movement permitted by the dog 96 and channel 98 ends from an open position in which fluid flow through the hydrant from the inlet 20 to the outlet 50 is permitted, and a closed position (shown in Figure 3) in which the gate 100 closes the outlet 59.

Following location of the replacement bonnet assembly 48 on the hydrant body 18, the deployment unit 56 is reconnected to the bag 46 through the outlet 50. The deployment unit is then secured and sealed to the outlet tube 51 (or the outlet tube 51 is dispensed with and the deployment unit connected directly to the upper housing 90). The deployment unit 56 is thus once again coupled and sealed to the hydrant and the valve 76 in the bag supply tube 59 can be reopened. The replacement bonnet assembly 48 optionally includes a tube 102, shown schematically and in broken outline in Figure 3, which is arranged to abut and seal against the valve seat 34. In this way, once the replacement bonnet assembly 48 has been mounted on the hydrant body 18, a sealed passage is provided extending up from the inlet 20, through the hydrant body 18 to the outlet 50. The tube thus defines part of the straight throughbore, and may facilitate insertion of equipment into the main 12 through the modified hydrant 10', as will be described below.

The bag 46 can then be deflated, pressure in the deployment unit 56 once again being balanced with mains pressure. The collapsed bag 46 is then withdrawn into the body 62 of the deployment unit 56; it will be understood that the curved guide tube 64 is typically disconnected from the body 62 prior to reconnecting of the deployment unit 56. The bag 46 thus passes through the outlet 50 and the sliding gate valve 80 may then be actuated to move the sliding gate 100 to the closed position, thereby closing the hydrant 10'. Mains pressure is once again vented through the valve 68 of the deployment unit 56, and the unit then removed from the hydrant 10'. The outlet tube 51 is then reconnected to the hydrant 10' (if appropriate) and a dust cap such as the cap 40 shown in Figure 1 mounted on the outlet tube 51. The hydrant is then ready either for normal operations, or an inspection and/or maintenance procedure may be carried out with the modified hydrant 10', which provides access to the main 12 through the straight throughbore defined between the inlet 20 and the outlet 50.

It will be understood from the foregoing description of the method of the present invention that a retrofit or replacement bonnet assembly 48 is also provided, which may be used in modifying a hydrant such as the hydrant 10 of Figure 1. Additionally, the invention relates to a hydrant 10' modified according to the above described method and incorporating the replacement hydrant 48.

Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention defined herein.

For example, other types of seal element may be employed. The seal element may be of a resilient material and/or may include a resilient portion, and may be arranged to be an interference fit with components of the hydrant or associated tubing in order to close the inlet.

The seal element may be arranged to close the inlet by sealing a part or parts of the hydrant body located on a flow path extending between the inlet and the outlet. For example, the seal element may be arranged to close the inlet by bridging across the hydrant body in a location above (or outwith) the inlet. This may require that the valve of the hydrant be opened, to provide a clearance between the valve and the valve seat in which the seal element may be located. It will therefore be understood that the method may not require that the seal element be directed into the inlet.

Whilst the method of the present invention and the associated retrofit bonnet assembly has been described in relation to a deviated bore hydrant of a particular type, it will be understood that the method and bonnet assembly may be applied to other types of deviated bore hydrant.

The retrofit bonnet assembly may comprise alternative valves to the sliding gate valve described above.