BACKGROUND ART In connection with large-scale water supply pipelines (e. g. a pipe of up to 4m diameter stretching thousands of kilometres), it is necessary to locate air release valve apparatus at regular intervals (e. g. every 600m). Such air release valves and associated instruments must be maintained and replaced periodically to ensure safe operation. It is not viable for the entire pipeline to be shut down for this maintenance and, therefore, butterfly valves are installed within a branch pipe located between the mainline and the air release apparatus (to block water flow to the apparatus and allow maintenance).

Figure 1 outlines a sketch of this prior art arrangement.

Branch pipe P is shown extending from a buried mainline M.

When servicing is required the butterfly valve B is closed to enable removal of the apparatus A. However, at pressures of up to 28 bar, a conventional butterfly valve can leak.

Furthermore, there is no way to access and service the butterfly valve itself without a total shut down of the pipeline.

DISCLOSURE OF THE INVENTION A need has been identified for a suitable valve that can enable apparatus A such as that illustrated by Figure 1 to be serviced, but also to be itself serviced in a satisfactory manner that does not involve shut-down of the pipeline. It is an object of the present invention to provide such a valve apparatus.

In one broad aspect of the invention there is provided a valve apparatus including a housing with a bore extending therethrough and a slot formed in a side wall of the housing to communicate with said bore, said slot being adapted to receive a first valve element therethrough which can, in use, substantially close flow through the bore, further including a second valve element which is adapted to substantially close flow through said slot.

In one form the slot can be closed with or without the first valve element in place within the bore.

Preferably the first valve element can be inserted into and left within the bore using a detachable means.

Preferably the second valve element can be inserted across the slot and left thereacross using a detachable means.

Preferably the second valve element includes a wedge-shaped element.

Preferably the first valve element is housed in a second detachable housing coupled over the slot of the (first) housing.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a sketch of a prior art pipeline, illustrating a conventional butterfly valve, Figure 2 is a perspective view of a housing according to the present invention, Figure 3 is a view (in phantom transparency) of a complete valve apparatus assembly according to the present invention, Figure 4 is a partially exploded view, Figure 5 is a further exploded view, Figure 6 is an assembled view of the first valve element in place and the second valve element withdrawn, Figure 7 is a view of the second valve element removed completely, and Figures 8-1 to 8-14 are a step-by-step illustration of a mode of operation according to the present invention.

MODE FOR CARRYING OUT THE INVENTION As stated above, an important requirement of the present invention is that the valve apparatus be capable of having its own mechanism serviced (maintenance or replacement) while a mainline is in use. This is possible by use of the valve apparatus as illustrated in Figure 2.

Figure 2 illustrates a housing (valve body) 10 that is to be coupled to a branch pipeline in place of the butterfly valve position as illustrated by Figure 1. Housing 10 is therefore to be between mainline M and apparatus A.

Housing 10 from Figure 2 is illustrated in its state as used in normal operation. A bore 11 is open for communication between mainline M and apparatus A (referring to the configuration of Figure 1). The unit is otherwise sealed.

In Figure 3 (phantom detail) a cover plate 12 has been removed and replaced by a second housing 13 (bolted onto housing 10) that now communicates with a slot 14 formed through a wall of housing 10 to communicate with bore 11. Within second housing 13 is a gate valve element 15 that may slide through slot 14 and effectively seal closed bore 11, by virtue of its dimensions (i. e. conforming to mate with an annular channel 16 formed within bore 11). A gate valve element 15 of this type is known per se. Suitable sealing means can be provided associated with channel 16 or one or both peripheral edges of the gate valve to improve the sealing characteristics and prevent leakage past the valve.

It will be apparent from Figure 3 that gate valve element 15 cannot freely move into slot 14/bore 11 until a second valve element in the form of"plug"17 is moved into a position wherein it no longer blocks thru-entry. This may be achieved by complete removal or, at least, withdrawal out of the female receiving portion within which the plug resides. The female receiving portion (channel) preferably has a diameter or other dimension that is at least wider than slot 14 as illustrated.

In the illustrated embodiment the plug 17 is conical or generally wedge shaped or tapered with a like-shaped female

channel to receive it. Such a shape has improved sealing properties in the present embodiment when the receiving face (female portion) of the valve is similarly shaped. A rubber coating on the plug 17 would account for any slight inconsistency in the machining of the female portion.

In alternative embodiments the plug could be a straight walled cylinder and have other features to withdraw and/or unblock the slot.

A withdrawn state of plug 17 is illustrated by Figure 6.

Withdrawal is effected by a screw threaded shaft 18 extending through an axis of plug 17. Shaft 18 is turned externally of a headworks cap 19 with room to accommodate plug 17 therein, which is sealed (bolted on) with housing 10 to prevent leakage.

When plug 17 is withdrawn gate valve element 15 may be extended to seal across bore 11, again by virtue of a threaded shaft 20 (see Figure 4) operated externally of the second housing 13.

Once gate 15 is in place within bore 11, flow therethrough to apparatus A (referring back to the configuration of Figure 1) is cut off. Plug 17, and headworks cap 19 can be removed for maintenance or replacement. Also, apparatus A can be removed or have maintenance performed thereon.

When maintenance is complete the procedure is reversed, i. e. apparatus A, plug 17 and cap 19 are refitted (in withdrawn position), gate 15 is withdrawn back into housing 13. This reopens flow through bore 11 to apparatus A. Plug 17 is extended to effectively close slot 14. Second housing 13 may then be unbolted and replaced by cover plate 12.

It will be appreciated that second housing 13 and its gate valve 15 may be then used on a different main housing 10 (which

is permanently affixed to the branch pipe P). This reduces overall cost because for a given length of mainline (with multiple access points) a maintenance team working on one apparatus A only needs one gate valve piece. It then moves onto the next access point and uses the same gate valve.

In a further embodiment plug 17 can be fixed at its narrow distal end 17a by a threaded shaft entering housing 10 from the opposite end 22 to headworks cap 19, whereupon cap 19 itself can be removed (with plug 17 still in place across slot 14) and replaced by a smaller cover piece 21 (see Figure 2).

When gate 15 is to be withdrawn from bore 11 (in the state of Figure 6), it may be necessary to use a pressure equalisation device 23 (Figure 4), e. g. in the form of a small spring-loaded ball, in the face of gate 15 to enable pressure to be equalised. This concept is generally known in the art.

Preferably the device 23 will be accessed from a wall of housing 10 opposite slot 14, this position being denoted 24 in Figure 4. A small through-hole to allow the spring-loaded ball to be"prodded"open is all that is necessary.

The remaining figures 8-1 to 8-14 show a simplified sequence of intended operation according to the present invention. A summary of each"configuration"is as follows: 8-1. The valve as it would be in operation prior to any requirement to shut off flow therethrough the bore (11).

8-2. The end plate (22) has been removed and replaced with a plug retaining screw that shall avoid any possible blowout.

8-3. The valve gate cover end plate (12) has been removed.

8-4. The plug can be seen through the window (slot 14).

Headworks cap (19) is fitted to the plug and bolted to the side of the valve body.

8-5. The valve gate housing (13) containing the valve gate (15) is fixed to the side of the valve body.

8-6. The plug is withdrawn via its screw mechanism into the headworks cap.

8-7. The valve gate (15) now closes the main aperture (bore 11) of the valve body. At this point any apparatus (A) can be inspected and maintained on the downstream side of the gate valve (15).

8-8. The valve plug (17) can be inspected for wear and replaced as necessary.

8-9. The headworks chamber (19) is re assembled. (Please note the valve gate housing (13) is not shown on drawing but it would be present).

8-10. The valve gate (15) is withdrawn into the valve gate chamber re-opening flow through the bore (11) and downstream of the valve assembly.

8-11. The valve plug is now inserted and the plug retaining screw (at 22) is tightened.

8-12. The headworks chamber (19) is removed and the outlet is capped (21) off on the valve body.

8-13. The plug retaining screw is removed and the end plate fitted.

8-14. The valve gate cover plate (12) is bolted to the valve body and the valve has been returned to its original configuration.

As will be apparent to those skilled in the art, the present invention provides an improved facility for maintenance and/or replacement of its own parts. The only part not directly replaceable without shut down of the pipeline is main housing 10. However, this can be designed to have a service life of at least 50 years through use of suitable materials, for example: Nickel Aluminium Bronze or Super Duplex Stainless Steel.

The other components can be made of suitable materials known in the art specific to sealing valves. The cone shaped plug 17 is preferably coated with a rubber layer. This is expected to perish over time, hence the need for a facility to check and replace as necessary without shutting the system down.

In general, the valve apparatus of the present invention has been developed for applications operating at around a maximum pressure of 30 bar (see"background"above). However, the preferred design has a capability of much higher pressures (e. g. up to 60 bar). It will be appreciated that different scales of the invention will have different capabilities.

INDUSTRIAL APPLICABILITY The valve apparatus according to the present invention has application in many pipeline supply industries, including water, gas and petrochemical. Furthermore, with suitable modification (incorporation of hydraulic power etc. ) the

invention can be scaled up or down for these further applications. The valve assembly is open to general iterative improvement by those skilled in the art using techniques known in the field of valve technology however, principally, the use of a"two-way"valve system to provide self maintenance as well as maintenance of other components in a pipeline is believed to be unique.