GB2449964A - Hydrant used to access water pipe for maintenance - Google Patents

Abstract

A hydrant 51 is used to gain access to a water pipe 50 to perform a maintenance operation on the pipe 50. The method is particularly suited for stopping water flow through a section of pipe by the insertion of an inflatable stopping bag 54 into the pipe 50 through the hydrant 51. A pressure regulator 60 is used so that the pressure in the inflatable bag 54 is proportional to the pressure in the pipe 50. A section of water main may be bypassed (figure 8) by blocking the main through two hydrants, and connecting the sections with a bypass pipe (70a, figure 8) that extends through the inflatable bags 54.

Description

METHOD OF PERFORMING A MAINTENANCE OPERATION ON A PIPE

The present invention relates to a method of performing a maintenance operation on a pipe. Particularly, but not exclusively, the present Invention relates to maintenance operations performed on a water mains or other pipe in a water supply network. More particularly still, the present invention relates to a method of blocking flow through a pipe such as a water pipe in a water supply network.

A variety of different maintenance operations (including operations to investigate, repair, or replace pipes or other fittings and equipment coimected to pipes), are frequently performed on pipe networks such as water supply pipe networks. Such operations often require earth to be excavated to expose a section of pipe and a hole drilled into the pipe wall to allow maintenance apparatus to be subsequently inserted into the pipe. For instance, it is common to carry out such operations on an in service pipe line by first stopping flow through the pipe by inserting pipe blocking apparatus into the pipe through a hole drilled in the pipe wall using well known drilling apparatus designed for operation under pressure.

One known form of pipe blocking apparatus comprises one or more inflatable stopping bags which are inserted into the pipe through a pre-drilled hole in the pipe wall and then inflated to form a sealed blockage in the pipe. Examples of such apparatus and pipe blocking methods are for instance disclosed in US 6,588,455 and EP 1 252 463.

It is a disadvantage of the known niethods of performing a pipe maintenance operation On a pipe discussed above that one or more holes must first be drilled in the pipe wall. It is an object of the present invention to provide a method of performing a maintenance operation on a pipe which does not necessarily require a hole to be drilled in the pipe wall.

According to a first aspect of the present Invention there is provided a method of performing a maintenance operation on a water pipe provided with a hydrant, the method comprising: inserting maintenance apparatus into the pipe through the hydrant.

Fire hydrants are installed in water mains or branch pipes to provide access to a water mains network for an emergency water supply for use in fire fighting. Fire hydrants can also be used to provide emergency water supplies in other cases, such as drought situations. For this purpose, fire hydrants are generally located at frequent intervals in readily accessible public areas to provide unencumbered access to the water supply in emergency situations. The present invention takes advantage of a suitably configured hydrant to provide access to a pipe to perform a maintenance operation without the requirement to first drill a hole in the pipe wall. There niay be some maintenance operations which require more than one access point, which could either be provided by two suitably located hydrants, or may require the drilling of at least one hole in the pipe wall in addition to the access provided by a hydrant (but even in such cases the number of holes that need to be drilled is reduced compared to

the prior art).

In accordance with one embodiment of the Invention the apparatus inserted into the pipe through the hydrant comprises apparatus for blocking fluid flow through the pipe, such as apparatus comprising an inflatable stopping bag device.

A preferred embodiment of the present invention comprises pressurising the bag using a pressure regulator which operates to regulate the pressure of the bag as a function of the instantaneous pressure in the pipe upstream of the stopping bag, and transmitting the pressure of the fluid in the pipe upstream of the stopping bag to the pressure regulator to provide the force required to pressurise the bag, wherein said pressure is transmitted via a pressure regulator conduit which extends through the bag and has an upstream end opening to the interior of the pipe upstream of the bag and a downstream end in fluid connection with the pressure regulator external to the pipe.

The present invention requires a hydrant provided with a flow passage through which maintenance apparatus can be inserted into the pipe.

One form of hydrant adapted for use in the method of the present invention comprises a housing defining an inlet, an outlet and a housing axis, and is designed to be mounted to a pipe so that the housing axis will extend generally perpendicular to the flow direction of the pipe, such that the housing axis extends through the inlet and the outlet.

Specific embodiments of the present invention will now he described, by way of example only, with reference to the accompanying drawings, in which: Figs I to 3 are sections through a hydrant adapted for use in a method in accordance with the present invention; Fig. 4 is an illustration of a known apparatus for blocking fluid flow through a pipe; Fig. 5 is a schematic illustration of a stopping bag apparatus inserted into a pipe in accordance with the present invention; Fig. 6 is an illustration of a stopping bag device inserted into a pipe in accordance with another embodiment of the present invention; Fig 7 is an illustration of a stopping bag device inserted into a pipe in accordance with another embodiment of the present invention; Fig. 8 is an illustration of a stopping bag device inserted into a pipe in accordance with another embodiment of the present invention; Figs. 9 to 12 are sections through a second example of a hydrant adapted for use in a method in accordance with the present invention; and Figs. 13 and 14 are sections through a third example of a hydrant adapted for use in a method in accordance with the present invention.

A first example of a hydrant suitable for use in a method according to the present invention is illustrated schematically in Figs. I to 3 and compnses a housing defining a chamber 21 provided with an inlet 22 and an outlet 23. The inlet 22 is surrounded by a mounting flange 24a to enable the hydrant to be connected to a flanged tee or the like of a water pipe (not shown), and the outlet 23 is surrounded by a flange 24b to which is bolted a threaded outlet neck 25. The inlet 22 is directly opposite the outlet 23 across the chamber 21 so that the inlet 22 and outlet 23 are aligned and the hydrant has a straight through-bore defined by the chamber 21 together with the inlet 22 and outlet 23. According to the normal orientation of the hydrant in use (in which the hydrant will typically be located in a submerged "box" in the upright orientation shown in Figs. 2 and 3), the outlet 23 will lie directly above the inlet 22 so that the through-bore 2 I, 22, 23 is substantially vertical.

Water flow through the hydrant inlet 22 to the outlet 23 is controlled by a valve member comprising an elastomenc coated valve plug 26 supported on arms 27, 28 each of which is pivotally mounted to the housing 20. A first arm 27 is supported on a stub shaft 27a which is pivotally received in a recess 29a in the wall of the housing 20, and a second arm 28 is supported on an axle 30 which extends through the wall of the housing diametrically opposite the stub shall 29. The stub shaft 29 and axle 30 define a pivot axis about which the valve member is pivotable by rotation of the axle 30. The pivot axis X is slightly offset relative to the housing, eccentrically disposed within the housing.

Fig. I shows the valve in a closed position in which the axle 30 has been rotated to pivot the plug 26 into engagement with a valve seat 31 defined by the housing around the mouth of the outlet 23. The plug 26 and valve seat 31 have the same profile geometry (circular in the illustrated example), and the compressible nature of the elastomeric coating on the plug 26 helps ensure a water tight seal between the two. In the illustrated hydrant the plug also has a bevelled profile edge 32 which further improves the sealing contact.

Figs. 2 and 3 show the valve in an open position in which the axle 30 has been rotated to pivot the plug 26 away from the valve seat 31 to a position adjacent the internal wall of the surface housing 1. In the illustrated hydrant the housing has a "bowled", or "barrelled" configuration to accommodate this pivoting movement of the valve member whilst maintaining a relatively compact housing The outlet 23 is thereby opened to allow water to flow through the hydrant.

The valve axle 30 may be rotated by a valve spindle (not shown) coupled to the axle 30 by a gear arrangement (not shown) for instance located externally of the housing 1. For example a gear box could be mounted to the housing I or could be integral with a modified housing I. An actuation member such as a vertically extending valve spindle (not shown) could be provided for rotating the axle 30 via such a gear arrangement (for instance a worm drive). A vertically extending valve spindle could for instance be positioned adjacent the hydrant outlet 23 for easy access.

Refemng again to Figs. 2 and 3, it will be seen that when the valve member is open the straight through bore defined by the chamber 21, inlet 22 and outlet 23 defines a straight line flow path between the inlet 22 and outlet 23 which is unobstructed by the valve member. As mentioned above, in the normal upright orientation of the hydrant in which the outlet 23 will lie above the inlet 22, the through bore 21, 22, 23 is substantially vertical. The present invention takes advantage of the straight through-bore 21, 22, 23 to provide convenient access to a water pipe to which the hydrant is fitted. Thus in accordance with the present invention, the illustrated hydrant may be used to provide a passage through which maintenance equipment may be inserted into a pipe to which the hydrant is fitted.

There are many routine circumstances in which access to the interior of a water pipe in situ in a water supply network is required to perform maintenance operations. For many such operations it is necessary to temporarily block water flow through the pipe and a variety of different methods and apparatus are known for achieving this which flrst require a hole to be drilled in the pipe wall through which the apparatus can be inserted into the pipe. Examples of such apparatus are for instance disclosed in US 6,588,455 and EP1252463 which disclose stopping bag devices for inserting and supporting an inflatable stopping bag into a water pipe through a pre-dn lied hole in the pipe wall.

In accordajice with the present invention it is not necessary to pre-drill a hole in the pipe wall, rather the stopping bag device (or other pipe maintenance equipment) is inserted into the pipe through the straight through bore defined through the hydrant.

Since fire hydrants are typically located at frequent intervals in a water supply pipe network, and in readily accessible public places, the use of hydrants according to the present invention provides numerous accessible access points into the pipe network.

Fig. 4 shows an example of known stopping bag apparatus taken from US 6,588,455 mounted to a pipe 40, for insertion through a hole 41 previously dnlled in the pipe wall. The apparatus comprises a stopping bag support device 42 mounted at the end of a stopping bag insertion tube 43 which is itself mounted within a conventional machine assembly 44 designed for the performance of various operations on a pressunsed water mains pipe. The machine assembly 44 comprises a machine base 45 which houses a sliding plate valve 46 and which may be secured to the pipe 40 by a chain or the like and sealed with respect to the pipe 40. The machine base 45 is of a universal nature providing a platform to which different apparatus can be mounted to perform operations on the pipe 40. The sliding plate valve 46 is provided to allow the hole 41 to be sealed as apparatus is removed and replaced on the machine base 45. The stopping bag support device 42 is inserted into the pipe through the hole 41 using a bag insertion assembly that includes an outer housing 47 mounted on the machine base 45. A stopping bag (not shown) is then inserted into the pipe 41 (in a deflated state) on the end of a bag inflation tube (not shown) through the bag insertion tube, and is then inflated within the pipe 40 to stop flow through the pipe.

It will readily be appreciated that in accordance with an aspect of the present invention, the machine base 45 could be easily modified for mounting on the hydrant rather than directly to the pipe. For instance, the machine base 45 could be modified for direct attachment to the outlet neck 25, or an adapter coupling (not shown) could be provided between the two. Alternatively, the neck 25 could be temporarily removed from the hydrant housing 20 and the machine base connected to the housing 20, for instance by secunng the machine base 25 to the outlet flange 24 or again providing an adaptor coupling between the two. Various possible coupling methods and appropriate modifications or alternatives to the machine base 25 could be devised by the skilled person without req uinng any inventive activity.

The maximum width or diameter of the apparatus that may be inserted into the pipe through the hydrant is hmited by the "pass- through" diameter of the through-bore defined through the hydrant by the chamber 21, inlet 22 and outlet 23 (assuming the outlet neck 24 is removed). The pass-through diameter is affected not only by the size of the inlet and outlet, hut also by their degree of alignment. For instance, in the hydrant llustrated in Figs I to 3, the inlet 22 and outlet 23 are aligned directly opposite one another so that the pass-through diameter is the diameter of the inlet 22 and outlet 23. If on the other hand the outlet neck 24 is in position, the smaller diameter of the outlet neck 24 will limit the maximum pass-through diameter.

Similarly, if the inlet 22 and outlet 23 are not directly opposite one another but are partially misaligned the maximum pass- through diameter will be less than the diameter of the inlet 22 and outlet 23 (and less than the diameter of the outlet neck 24 if fitted), although may still be large enough to allow insertion of pipe maintenance apparatus (such as stopping bag devices) into the pipe. With the illustrated hydrant there is at least one straight line which may be drawn through the inlet 22 and outlet 23 and which will extend substantially perpendicular to the axis of the pipe to which the hydrant is fitted. Put another way, when normally orientated there will be a substantially vertical straight line path between the inlet 22 and outlet 23.

Fig. 5 is a simplified schematic drawing illustrating a stopping bag device of the general type described above inserted into a pipe 50 through a hydrant 51 according to a method of blocking a pipe in accordance with the present invention. A machine assembly similar to the machine 4 and machine base 5 may be used to support and install the stopping bag device but such details are omitted from Fig. 5 for clarity. Other details of the stopping bag device, which may be entirely conventionally, are similarly omitted or simplified for clarity. The hydrant 51 is mounted to the pipe 50 by securing (e.g bolting) the hydrant inlet flange 24a to a pipe tee flange 52. Similarly the hydrant valve member is omitted for clarity.

The hydrant outlet neck 25 has first been removed to increase the size of the hydrant through-bore as mentioned above (this is an optional step to increase the size of the hydrant through-bore if necessary). Axle 30 is rotated to pivot the valve member into the open position thus opening up the through-bore. Stopping bag insertion tube 53 is then inserted into the pipe 50 though the hydrant 51.

Subsequently a stopping bag 54 is inserted into the pipe 50 through the bag insertion tube 53 on the end of a flexible inflation tube 55 which extends through the bag 54 and terminates in a nosepiece 56 which helps protect the bag 54 as it is guided into position in the pipe 50. Pressurised fluid such as a pressunsed air or water is delivered to the bag 54 from a fluid source (not shown) via an inflation hose 57 connected to the bag insertion tube 53 by coupling 58 to inflate the bag 54. The inflation tube has holes 59 to allow the pressunsed fluid to enter the bag 54. Once inflated the bag 54 blocks flow through the pipe 50. This allows a maintenance operation to be performed on the pipe or any fitting connected to the pipe downstream of the bag 54. For instance, such a maintenance operation may involve inserting further apparatus into the pipe through the hydrant, if necessary first removing the bag insertion apparatus.

Some apparatus which may need to be inserted into a pipe during a maintenance operation requires more than one entry point into the pipe. In such cases, if there are hydrant valve locations sufficiently close together access may be made into the pipe at these two (or more) locations. Alternatively, it may be necessary to drill a hole in the pipe wall close to a single hydrant and some apparatus inserted through the drilled hole in addition to apparatus inserted through the hydrant Fig. 6 is a simplified schematic drawing illustrating a stopping bag device of the general type disclosed in EP1252463 installed in a pipe by a method in accordance with one embodiment of the present invention in which the stopping bag is inserted through a hydrant and a separate tapping is made to supply water to a pressure regulator. The apparatus is illustrated as a simple modification of the apparatus shown in Fig. 5 and the same reference numerals are used where appropriate.

Referring to Fig. 6, (and bearing in mind that details such as the bag insertion assembly and associated machine housing and machine base etc are again omitted for clarity) the illustrated apparatus comprises a stopping bag 54 installed in a pipe 50 via a bag insertion tube 55 which extends into the pipe 50 through a hydrant 5 1. The bag 54 is subsequently inflated to form a blockage in the pipe 50, and pressure within the bag 54 is regulated via an inflation tube 57 which is connected to a pressure regulator 60.

The pressure regulator is of the type disclosed in EP1252463 and comprises a cylinder 60a within which is mounted a piston assembly 61. The cylinder 60a has a relatively large diameter chamber 62 and a relatively small diameter chamber 63, an annular shoulder 64 being defined where the two chambers meet (approximately mid-way along the axis of the cylinder 60a).

The piston assembly 61 comprises two connected pistons 61 a and 61 b. Each of the pistons 61a and 61b comprises a disc which is sealed with respect to the internal wall of the cylinder 26, for instance by piston rings (not shown). The piston 61a has a larger diameter than piston 61b and is in sliding engagement with the larger diameter cylinder chamber 62. The smaller diameter piston 61b is in sliding engagement with the smaller diameter cylinder chamber 63. The piston assembly 61 is free to slide within the cylinder 60a so that the working volumes of the cylinder chambers 62 and 63 are variable. The pistons 61a and 61b are constrained to slide within the cylinder chambers 62 and 63 respectively by the relationship between the axial length of the piston assembly 61 and the axial length of the cylinder 60a.

The pressure regulator 60 has an inlet 65 which opens into the bottom of the large diameter cylinder 62. The inlet 65 is coupled to a pipe 66 which taps into the pipe 50 at a nipple 67 installed in a pre-drilled hole in the pipe wall for this purpose.

The pressure regulator has an outlet 68 which communicates with the smaller diameter cylinder chamber 63 and is connected to the bag inflation tube 53 via inflation hose 57.

The bag 54 may be inflated by water forced into the bag from the pressure regulator 60 by filling the cylinder chamber 63 prior to connection of the regulator to the bag inflation tube 53. When the regulator inlet pipe 30 is then connected to the pipe 30a, water pressure within the cylinder chamber 62 rises to that of the water within the pipe 50 upstream of the bagging apparatus. This exerts a force on the piston 61a which is greater than that exerted on piston 61b by the water pressure within cylinder chamber 63. The piston assembly 61 is driven upward by this force difference thereby forcing water out of the cylinder chamber 63 and into the bag 54 to inflate the bag 54.

As the bag 54 is inflated the pressure within the bag, and thus within the cylinder chamber 63, increases. The piston assembly 61 will continue to force water into the bag 54 until the force exerted on the piston 61b equals that exerted on piston 61a, i.e. equilibrium is reached. It will, however, be appreciated that the force exerted on each piston is a function of the pressure within the respective cylinder chamber 62, 63 and the surface area of each piston 61a, 6lb. Thus, since the piston 61b has a smaller surface area than the piston 61a, the pressure in chamber 63 will be higher than the pressure in chamber 62 when the equilibrium is reached. The pistons are relatively sized in this way to ensure that the pressure within the bag 54 is slightly greater than that within the pipe 50 to provide an effective seal. Indeed, it has been found that to provide an effective seal the bag 54 should preferably be pressurised to approximately 1.18 times the pressure within the pipe 50 upstream of the bag 54.

This is readily achieved by ensuring that the area of the piston 61a is 1.18 times as big as the area of piston 61b.

Once the bag 54 has been inflated, the pressure within the bag 54 is automatically regulated as a function of the pressure upstream of the pipe. That is, if the pressure in the pipe 50 drops the pressure in the chamber 62 will drop so that the force exerted on the piston 6la will decrease allowing water to be forced back into the chamber 63 from the bag 54 until the force across the piston assembly 61 has again been equalised. The reverse will of course occur should the pressure in the pipe increase. It will be appreciated that as the pressure fluctuates in the pipe a corresponding fluctuation will occur in the pressure of the bag 54 which will always remain at a predetermined proportion of the pressure in the pipe 50 (e.g. 1.18 times greater than the pressure in the pipe).

Thus, the pressure regulator 60 can be operated both to inflate the bag 54 and to ensure that the pressure within the bag is regulated as a function of the pressure in the pipe 50 upstream of the bag installation. Moreover, the particular pressure regulator illustrated achieves this without the requirement for any external power source, since the driving force is provided by the water pressure within the pipe 50.

It will be appreciated that the pressure regulator need not be used to initially inflate the bag 54 but may be connected to a pre-inflated bag to provide pressure regulation only. It will also be appreciated that valves may be provided in the conduits between the regulator 60 and pipe 50 and between the regulator 60 and inflation tube 53, to control flow to and from the regulator 25, and that further connections may be made to these conduits.

The above described method according to the present invention provides an advantage over the method described for instance in EP1252463, in that the stopping bag apparatus is inserted into the pipe 50 through the hydrant so that only a single hole is required to be drilled in the pipe (to provide the connection to the pressure regulator 60). According to a further embodiment of the present invention there is provided a modification of the above method of blocking flow through a pipe which does not require even one hole to be dnlled in the pipe. This will now be descnbed with reference to Fig. 7 which illustrates a modification of the apparatus of Fig 6 installed in a pipe by a method in accordance with the present invention. Again the drawing is a simple schematic drawing and features corresponding to features of Fig. 6 are identified using the same reference numerals.

The bag inflation tube 55 is modified to include a coaxial tube 70 which extends the whole length of the inflation tube 55. An upstream end of the tube 70 extends through a bore provided through a modified insertion tube nosepiece 71 and is open to the interior of the pipe 50 upstream of the bag 54. A downstream end of the tube 70 is coupled to the inlet pipe 66 to the pressure regulator 60 via a coaxial connector 72 which replaces the coupling 58 of Fig. 6. The coaxial connector 72 is generally cylindrical with an axial opening 73a which allows the tube 70 to extend through the coupling 72 into the end of the connected inlet pipe 66. The coaxial connector 72 also couples the inflation hose 57 to the inflation tube 55 via a lateral opening 73b that allows the connected inflation hose 57 to communicate with an annular inflation conduit 74 defined within the inflation tube 55 between the wall of the inflation tube 55 and the wall of the tube 70.

The tube 70 provides a conduit for transmitting fluidlfluid pressure from within the pipe 50 immediately upstream of the bag 54 to the regulator 60. This avoids the need to make a separate tapping into the pipe 50 to provide communication between the pipe 50 and regulator 60. Accordingly, all of the equipment necessary for stopping the flow through the pipe 50, including the stopping bag insertion apparatus, the stopping bag itself, and the means for regulating the pressure in the stopping bag, is inserted through the hydrant 5 1 and there is no requirement to drill a hole through the wall of the pipe 50.

The tube 70 may be coaxially fitted within the inflation tube 55 and inserted into the pipe 50 together with the inflation tube 55. Alternatively the tube 70 could be inserted into the inflation tube 55 after the inflation tube 55 has been inserted into the pipe 50.

Other than the nature of the connection between the pipe 50 and inlet 65 of the regulator 60, the apparatus of Fig. is operated in same way as the apparatus of Fig. 6.

It will be appreciated that the tube 70 need not be coaxial within the inflation tube 55 but could for instance be disposed alongside the inflation tube and could for example be bound to the inflation tube 55 and extend with it into the bag 54. The tube 70 could then open into a suitably modified nosepiece providing communication with the pipe 50 upstream of the bag, or could open into the pipe 50 through a separate aperture provided in the wall of the bag 54.

In some circumstances, it is necessary, or desirable, to isolate a section of an in-service pipeline for maintenance whilst maintaining service downstream of the isolated section. This can be done by inserting stopping bags into two locations in the pipeline, to isolate the section to be operated on, and provide a temporary bypass pipe for allowing water flow to bypass the isolated section of pipe. A modification of the apparatus of figure 7 which achieves this as illustrated in figure 8. This shows two identical sets of stopping bag apparatus A and B installed through respective hydrants 51 at upstream and downstream locations in an in-service pipe 50 respectively. The stopping bag apparatus A and B are very similar to the apparatus illustrated in figure 7, and thus the same reference numerals are used where appropriate. The only significant difference between the apparatus of figure 8 and figure 7 is that with the apparatus of figure 8 the tubes 70 of each apparatus A and B are connected together by a bypass tube 70a. The inflation hose 57 of each apparatus A and B is connected to the respective bag inflation tube 55 by a coaxial connector 72 which also connects each tube 70 to the bypass tube 70a. Respective pressure regulator inlet pipes 66 are connected to the bypass tube 70a. Accordingly, the coaxial tubes 70 not only transmit water pressure to the pressure regulator in order to control pressurisation of the bags 54, the tubes 70 and bypass tube 70a together also provide a bypass flow path to allow flow to bypass the isolated section of pipe so that the pipeline may remain in service.

The particular form of pressure regulator illustrated in Figs. 6 to 8 is advantageously simple in construction and operation. It can be employedin the relatively hostile environments that may be found when working on pipe lines requiring no supervision and little maintenance. A particularly important advantage of the regulator illustrated is that it requires no external power source as the driving force is provided by the water within the pipe line 50. It will be appreciated, however, that many modifications could be made to the regulator. For instance, the relative sizes of the pistons can be altered to modify the ratio of the pressure within the pipe line 50 and within the bag 54. Other details of the particular piston arrangement can of course vary widely. The function of this particular type of regulator in which the water pressure in the bags is controlled directly as a function as the pressure in the pipes just requires two pistons mechanically linked together. For instance, the two pistons could move in quite separate chambers, The connections to the regulator illustrated could be modified to take advantage of the water in the pipe to fill the chamber 63 prior to inflation of the bag 54.

Although the methods of performing a maintenance operation on a pipe in accordance with the present invention have been exemplified by installation of stopping bag systems, it will be appreciated that any other appropriate pipe maintenance apparatus may be inserted through the hydrant valve and that the invention is not limited to methods of stopping flow through a pipe.

it will also be appreciated that details of the illustrated hydrant may vary widely. For instance, the valve member could be arranged to engage with a valve seat provided around the mouth of the hydrant inlet 22 rather than the hydrant outlet 23 in order to close the hydrant. Although it is preferred that the hydrant inlet 22 and outlet 23 are directly aligned to maximise the diameter of the through-bore through the hydrant, a certain degree of misalignment is acceptable provided there is still a through-bore of sufficient size to accommodate pipe maintenance apparatus. The housing 20 may therefore vary in detailed design, as may the details of the valve member and its actuation.

An example of an alternative hydrant adapted for use in a method in accordance with the present invention is illustrated in Figs. 9 to 12. Figs. 9 and 11 are cross-sections through a hydrant in open and closed configurations respectively.

Figures 10 and 11 are plan views of the hydrant in the open and closed positions of Figs. 9 and 11 respectively. The modified hydrant comprises a housing 80 defining a chamber 81 having an inlet 82 and an outlet 83. A mounting flange 84 is defined around the inlet 82 for mounting the hydrant to a pipe tee or the like. An outlet neck is coupled to the inlet 83 for connection of the fire hose or the like. The hydrant differs from the hydrant of the Figs. Ito 8 in the configuration of the housing 80 and the nature of the valve member used to control flow through the housing. In place of the eccentric pivoting plug alve member there is a sliding plate valve member 86 which is mounted to a pivot axle 87. They hydrant defines a straight through-bore comprising inlet 82 a cylindrical housing chamber 81 and outlet 83.

When in a closed position as illustrated in Fig 9. the valve plate member 86 extends across the chamber 81 and is sealed with respect to the housing by seal members 88. To open the hydrant, the pivot axle 87 is rotated to slide the valve plate 86 into a valve member cavIty 89 defined to one side of the valve chamber 81 as illustrated in Figs. 10 and 12. This opens the flow path through the hydrant and in particular leaves the through-bore unobstructed.

Another example of a hydrant suitable for use with the present invention is illustrated in Figs. 13 and 14 which illustrate the hydrant in open and closed configurations respectively. In this case, the hydrant includes a flap valve member 96 which is pivotally mounted on an arm 97 within a modified hydrant housing 90. The hydrant housing defines a chamber 91 having an inlet 92 and outlet 93. Once again, the inlet 92 is surrounded by a mounting flange 94 and the outlet 93 is fitted with an outlet neck 95.

In the closed configuration illustrated in Fig. 13 the flap valve member is pivoted into connection with a valve seat 98 defined around the mouth of the hydrant outlet 93 The plate valve member 96 has a coating of elastomcric material 99 to ensure a good water tight seal with the valve seat 98. The support arm is mounted on a valve axle 100 which may extend from the housing into engagement with a valve spindle (not shown), for instance via a gear box (e.g. a worm drive) in a similar manner to that described above in relation to the hydrant of Figs. I to 3.

The hydrant is opened by rotation of the axle 100 to pivot the valve member away from the valve seat 98 and into a cavity 100 defined by the housing 90 to one side of the hydrant through bore defined by the inlet 92 chamber 91 and outlet 93.

It will be appreciated that the installation, operation and use of the hydrants illustrated in Figs. 9 to 12 and 13 to 14 may be essentially the same as that of the hydrant as illustrated in Figs. 1 to 7.

It will also be appreciated that many detailed changes could be made to the structure of the illustrated hydrants, and that alternative forms of valve member may be incorporated in other examples of hydrants suitable for use with the present invention.

Other possible modifications will he readily apparent to the appropriately skilled person.

Claims (20)

1. A method of performing a maintenance operation on a water pipe provided with a hydrant, the method comprising: inserting maintenance apparatus into the pipe through the hydrant.

2. A method according to claim 1, wherein said maintenance apparatus comprises apparatus for blocking water flow through the pipe.

3 A method according to claim 2, wherein said apparatus comprises an inflatable stopping bag, the method comprising inserting the stopping bag into the pipe through the hydrant and subsequently inflating the stopping bag within the pipe to form a blockage in the pipe upstream of the hydrant.

4. A method according to claim 3, wherein the inflatable stopping bag is inserted into the pipe on the end of a bag inflation tube which is inserted through said hydrant

5. A method according to claim 3 or claim 4, wherein the inflatable stopping bag is inserted into the pipe through a bag insertion tube which is inserted through the hydrant.

6. A method according to claim 4, wherein at least an insertion end of the bag inflation tube is substantially rigid to provide a support for the inflatable bag within the pipe.

7. A method according to claim 5 or 6, wherein at least a portion of the insertion tube which extends through said hydrant when said insertion tube is inserted into the pipe is at least substantially rigid.

8. A method according to any one of claims 3 to 7, compnsing pressunsing the bag using a pressure regulator which operates to regulate the pressure of the bag as a function of the instantaneous pressure in the pipe upstream of the stopping bag, and transmitting the pressure of the fluid in the pipe upstream of the stopping bag to the pressure regulator to provide the force required to pressunse the bag, wherein said pressure is transmitted via a pressure regulator conduit which extends through the bag and has an upstream end opening to the interior of the pipe upstream of the bag and a downstream end in fluid connection with the pressure regulator external to the pipe

9. A method according to claim 8, wherein said stopping bag is mounted to a bag inflation tube for insertion through the hydrant into the pipe and for the supp]y of pressurised fluid to inflate the bag within the pipe, wherein said pressure regulator conduit is bundled together with the inflation tube.

10. A method according to claim 8, wherein said stopping bag is mounted to a bag inflation tube for insertion through the hydrant into the pipe and for the supply of pressunsed fluid to inflate the bag within the pipe, wherein said pressure regulator conduit is coaxial with the inflation tube.

11. A method according to claim 9 or 10, wherein said pressure regulator conduit is coupled to the inflation tube prior to insertion through the hydrant.

12. A method according to any one of claims 3 to 11, compnsing inserting a second stopping bag into the pipe through a second hydrant to isolate a section of pipe for maintenance.

13. A method according to claim 12, wherein the first hydrant is upstream of the second hydrant, and a temporary bypass pipe is connected between the pipe upstream of the first stopping bag and downstream of the second stopping bag to allow water flow to bypass the isolated section of pipe during the maintenance operation.

14. A method according to claim 13 when dependant from any one of claims 8 to 11, wherein the bypass pipe is connected between the pressure regulator conduit of the first stopping bag and the pressure regulator conduit of the second stopping bag so that the bypass flow passes through each pressure regulator conduit.

1 5. A method according to any preceding claim, wherein the hydrant comprises a housing defining an inlet, an outlet and a housing axis and is mounted to the pipe such that the housing axis extends generally perpendicular to the flow axis of the pipe, wherein said housing axis extends through said inlet and said outlet and the maintenance apparatus is inserted through the hydrant in a direction generally parallel to the housing axis.

16. A method according to claim 15, wherein the hydrant inlet comprises an aperture defined in a wall of the housing and the outlet comprises an aperture defined in a wall of the housing, and wherein the inlet and the outlet are positioned such that said housing axis extends substantially through the centre of the inlet aperture andlor the centre of the outlet aperture.

17. A hydrant according to claim 15 or claim 16, wherein the hydrant comprises a valve member disposed within said housing and moveable between a closed position in which it blocks fluid flow through the hydrant, and an open position in which it permits fluid flow through the housing, and wherein when in said open position there is a straight passage through the inlet and outlet parallel to said housing axis substantially unobstructed by the valve member through which the maintenance apparatus is inserted.

18. A hydrant according to claim 17, wherein said passage has a maximum diameter or width equal to at least half of the diameter or width of the inlet andlor of the outlet.

19. A hydrant according to claim 18, wherein said passage has a diameter or width at least equal to the diameter or width of the inlet and/or the outlet.

20. A hydrant according to any one of claims 15 to 19, wherein the hydrant member is pivotably mounted within said housing on an axle extending through a housing wall, whereby rotation of said axle moves said valve member between open and closed positions, and wherein the valve member is moved into the open position to permit insertion of the maintenance apparatus