FIELD OF INVENTION This invention relates to an air release valve for a liquid pipeline.

SUMMARY OF INVENTION According to a first aspect of the invention there is provided an air release valve for a liquid pipeline, comprising: a valve body having an upper end and a lower end and defining a valve chamber, the valve body having an inlet at its lower end and an outlet at its upper end; a control float movably located in the valve chamber, the control float being movable in response to changes in liquid level in the valve chamber; an upper valve member movably located in the valve chamber above the control float, the upper valve member having an air vent passage which is in register with the outlet and which is smaller in size than the size of the outlet; a lower valve member movably located in the valve chamber above the control float and below the upper valve member, the lower valve member having an air vent passage which is in flow communication with the air vent passage of the upper valve member and which is smaller in size than the size of the air vent passage of the upper valve member, the upper valve member being characterized in that it has a projecting air abutment formation against which air flowing operatively upwardly in the valve chamber during filling of the pipeline with liquid, impacts, for exerting a lifting force on the upper valve member for assisting in lifting up the upper valve member to seat against the outlet thereby to reduce the size of the outlet through which the air can flow.

The upper and lower valve members may be generally disc-shaped with at least part of the upper valve member projecting radially outwardly beyond a side of the lower valve member, so as to provide an overhang which is impacted upon by air flowing upwardly in the valve chamber exerting a lifting force on the upper valve member.

The air abutment formation of the upper valve member may include a circumferential lip formation depending from a lower peripheral edge region of the upper valve member.

The air release valve may include an annular valve seal located around the air vent passage of the upper valve member at an upper side of the upper valve member so as to form an air-tight seal around the air vent passage of the upper valve member and the outlet of the valve body when the upper valve member is seated against the outlet.

The air release valve may include an annular valve seal located around the air vent passage of the lower valve member at an upper side of the lower valve member so as to form an air-tight seal around the air vent passages of the upper and lower valve members when the lower valve member is seated against the upper valve member. The control float may have a valve seat for closing-off the lower end of the air vent passage of the lower valve member.

The lower valve member may be configured to be lifted up together with the control float to seat against the upper valve member, when the lower valve member and the control float are buoyed up by liquid within the valve chamber when air has been evacuated from the valve chamber.

A lower peripheral edge region of the control float may be convexly rounded.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of a prior art air release valve and further features of the invention are described hereinafter by way of a non-limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a sectional side view of a prior art air release valve, illustrating its mode of operation in an initial stage of a pipeline to which the valve is connected, being filled with a liquid;

Figure 2 shows a sectional side view of the prior art valve of Figure 1 , illustrating the operation of the valve for venting air out of the pipeline if the pipeline is filled too quickly with liquid;

Figure 3 shows a sectional side view of an air release valve in accordance with the invention, illustrating the position of the control float and the valve members at an initial stage of filling of a water pipeline to which the air release valve is connected; Figure 4 shows a sectional side view of the air release valve of Figure 3, illustrating the position of the valve members and the control float when the pipeline is filled too quickly with water;

Figure 5 shows a sectional side view of the air release valve of Figure 3, illustrating the position of the valve members and the control float when water has entered the valve chamber and air has been evacuated therefrom;

Figure 6 shows a sectional side view of the air release valve of Figure 3, illustrating the position of the control float in its lowermost position and the valve members, during normal pressurized operation after filling of the pipeline;

Figure 7 shows a sectional side view of the pipeline of Figure 3, illustrating the position of the control float and the valve members when the pipeline is being drained, to allow air to flow into the pipeline in order to prevent a vacuum;

Figure 8 shows a sectional end view of the air release valve of Figure 3, sectioned along section line VIII-VIII of Figure 3;

Figure 9 shows a sectional end view of the air release valve of Figure 3, sectioned along section line IX-IX of Figure 3; and

Figure 10 shows a sectional end view of the air release valve of Figure 3, sectioned along section line X-X of Figure 3.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 and 2 of the drawings, a prior art air release valve for a water supply pipeline, is shown in two modes of operation. The prior art air release valve is designated in the drawings by the reference numeral 10. The valve 10 comprises a valve body 1 1 defining a valve chamber 12, control float 13, a lower valve member 14 and an upper valve member 15 located in the valve chamber. The valve body defines an inlet opening 16 at a lower end which is connected to a water supply pipeline and an outlet opening 17 at an upper end thereof, which is open to the atmosphere. The lower and upper valve members define vent passages 18.1 and 18.2, respectively, wherein the diameter of the vent passage 18.1 provided by the passage through nozzle insert 19, is less than the diameter of the vent passage 18.2, both vent passages having a smaller diameter than the diameter of the outlet opening 17.

A prior art air release valve of this type is disclosed in South African Patent 94/1452. The Applicant has identified a problem with the switching rate at which such air release valves switch to the smaller‘anti-shock orifice’ defined by the upper valve member. This is particularly a problem with relatively large air release valves typically used on steeper sections of a water supply pipeline, wherein the switching rate of such valves may be too high to protect the pipeline against potential water hammer caused by the valve slamming shut. In this specification, the term“switching rate” means the air flow rate within the valve chamber at which the upper valve member is lifted dynamically against the outlet opening of the valve due to differential air pressures acting across the upper valve member caused by a relatively lower pressure region which is created above the upper valve member when air flows through the valve chamber and out through the outlet opening 17. More specifically, even if the pipeline is filled too rapidly exposing the pipeline to potential water hammer damage, the air flow rate in such relatively large valves, may not be sufficient to activate the anti-shock orifice by lifting the upper valve member against the outlet opening.

With reference to Figures 3 to 7, an air release valve in accordance with the invention, is designated generally by the reference numeral 20. The air release valve 20 is configured for use with a water supply pipeline. The air release valve 20 comprises a valve body 22 defining a valve chamber 24, a control float 26, a lower valve member 28 in the form of a kinetic float and an upper valve member 30 in the form of an anti-shock float. The control float and the upper and lower valve members are located within the valve chamber.

The valve body 22 defines a longitudinal axis A and has an operative upper end 32 and an operative lower end 34. The valve body has a cylindrical side wall 36, a top flange plate 38 which defines the upper end 32 of the valve body and a bottom flange plate 40 which defines the lower end 34 of the valve body. The top and bottom flange plates are secured to the top and bottom ends, respectively, of the side wall.

The bottom flange plate 40 defines a central inlet opening 42 which is connectable to a stand pipe in flow communication with a water pipeline. The air release valve is mounted to the pipeline at a high point in the pipeline. The air release valve includes a baffle plate 46 which is located in the valve chamber and at a location spaced from the bottom flange plate 40. The control float 26 rests on an upper side of the baffle plate 46 in a lowered position of the control float. The baffle plate defines four centrally located apertures 47 which allow water and air to flow therethrough.

The air release valve includes four circumferentially equi-spaced tie rods 49 which extend between the top and bottom flange plates. Lower end regions of the tie rods are screw-threaded to receive nuts 50 for supporting the baffle plate 46. More specifically, the baffle plate defines holes through which the tie rods pass. Sleeves 53 are located on the tie rods at lower ends thereof for spacing and supporting the baffle plate at a spaced location above the bottom flange plate.

The top flange plate 38 defines a central outlet opening 52 which is in communication with the atmosphere.

The valve members 28 and 30 and the control float 26 are axially displaceable within the valve chamber 24. The valve members and the control float are of a material which is buoyant in water. The control float is cylindrical in shape and has a cross-sectional diameter which is less than the internal diameter of the side wall 36. A lower peripheral edge region of the control float is convexly rounded. The control float 26 has a valve seat 54 disposed axially near its upper surface. The valve seat is located within a central recess defined in an upper side of the control float. The valve seat 54 comprises an upper valve seal 56, a retaining circlip 57 and a lower compression spring 58 which urges the valve seal upwards. The valve seal 56 is in the form of a cylindrical seal body movably received within the central recess in the control float. The valve members 28 and 30 have axial vent passages 60 and 62, respectively.

The lower valve member 28 is cylindrical and generally disc-shaped and carries an O- ring seal 66 on its upper surface. The lower valve member has a cross-sectional diameter which is the same as the cross-sectional diameter of the control float. The lower valve member 28 includes a nozzle insert 64 which is located in the vent passage 60 and which defines an internal diameter of the vent passage 60. The effective diameter of the air vent passage 60 is provided by the relatively smaller diameter of the passage defined by the nozzle insert 64 and is less than the diameter of the vent passage 62. The nozzle insert 64 has a lower end which projects below the bottom side of the valve member and which is seated on the valve seal 56 of the valve seat 54 of the control float when the lower valve member rests on the control float or the control float is buoyed up against the lower valve member. The spring 58 urges the valve seal 56 into sealing contract with the lower end of the nozzle insert 64. In the seated position of the lower valve member on the control float, the lower end of the vent passage 60 is thus sealed closed.

The upper valve member 30 is cylindrical and generally disc-shaped and carries an O- ring seal 68 on its upper surface. The upper valve member has a cross-sectional diameter which is less than the internal diameter of the side wall 36. As such, an annular space is defined between the control float, the valve members and the side wall 36 of the valve body. The cross-sectional diameter of the upper valve member is larger than the cross-sectional diameter of the lower valve member thereby defining a projecting annular air abutment formation which is acted upon by air flowing upwardly in the annular space between the control float and the valve members and the side wall 36 of the valve body. A central lower end region of the upper valve member is recessed providing the air abutment formation with a circumferential lip 70 which depends from a lower region of the valve member.

The rounded shape of the lower peripheral edge region of the control float 26 promotes upward air flow along the side of the control float in close proximity to the side of the control float thereby to facilitate the upward airflow impacting the air abutment formation.

The air release valve 20 includes a top cover plate 72 which is spaced above the outlet opening 52.

The modes of operation of the air release valve are described hereinbelow:

With reference to Figure 3, during filling of the pipeline with water, the valve members 28 and 30 and the control float 26 are initially disposed in lowered positions wherein the control float rests on the baffle plate 46. As the pipeline is filled with water, air which is displaced within the pipeline by water, enters the air release valve and is vented from the valve through the outlet opening 52 to atmosphere. Due to the relatively large size of the outlet opening, large volumes of air are vented from the pipeline, the air following the path in the annular space defined between the control float and the valve members and the side wall of the valve body, as illustrated by the arrows in the drawings. This mode of operation of the air release valve also occurs subsequent to an abrupt cessation of displacement of water in the pipeline caused, for example, by tripping of a water pump causing air to enter the pipeline.

As filling of the pipeline continues, there is a build up of air pressure within the air release valve. Air flow across the upper valve member causes a pressure differential across the upper valve member caused by a lower pressure above the upper valve member. The pressure differential exerts a lifting force on the upper valve member. In addition, air flowing upwardly along the annular space within the valve chamber impacts the overhang provided by the large diameter of the upper valve member. Furthermore, the depending lip 70 of the upper valve member causes air to collect within the recess formation defined within the peripheral lip thereby increasing air pressure on a lower side of the upper valve member. When the air flow rate within the valve chamber reaches a predetermined value, the upper valve member is lifted upwardly into sealing engagement with the top flange plate 38 of the valve body (Figure 4). In this raised position, the vent passage 62 is in register with the outlet opening 52, thereby effectively reducing the size of the outlet opening. The smaller outlet orifice provided by the vent passage 62, restricts air flow through the valve and causes a pressurised“air cushion” in the pipeline. This air cushion slows down an approaching column of water within the pipeline during filling of the pipeline, thereby reducing the potential for water hammer effects by absorbing water hammer forces within the pipeline which may cause damage to the pipeline and/or the air release valve.

With reference to Figure 5, when the air has been evacuated from the air release valve, water enters the valve chamber 24 and the control float 26 is buoyed up by the water taking the lower valve member up with it, thereby closing the outlet opening 52. In this position of the control float and the valve members, water is prevented from flowing out through the outlet opening 52.

During normal pressurised operation of the pipeline, air is entrained in the water and pockets of air form in the pipeline and need to be vented from the pipeline. This air collects in an upper region of the valve chamber. As additional air collects in the upper region of the valve chamber, the water level in the valve chamber drops causing the control float 26 to drop as is shown in Figure 6. Air is vented through the outlet opening 52 via the vent passages in the upper and lower valve members. The upper and lower valve members maintain their raised positions as described above for as long as the air pressure within the valve chamber exceeds atmospheric pressure and the differential air pressures across the valve members are sufficient to overcome the mass of the valve members and keep the valve members in their raised positions.

With reference to Figure 7, should a sub-atmospheric pressure condition develop in the pipeline, the control float 26 and the valve members 28 and 30 drop and come to rest on the baffle plate 46, thereby opening the outlet opening to its fullest extent and allowing atmospheric air to enter the pipeline via the outlet opening 52 to equalise the pressure in the pipeline. The larger diameter of the upper valve member 30 relative to the diameter of the lower valve member and the provision of the circumferential lip 70, provide the upper valve member with a projecting annular air abutment formation, which ameliorates the abovementioned problems associated with the prior art valves. More specifically, the upper valve member is lifted during pipeline filling by the combined effect of the pressure differential across the valve member and the impact of air flowing upwardly in the valve chamber on the air abutment formation of the upper valve member due to the greater diameter of the upper valve member and the provision of the depending circumferential lip 70.