GB2398887A - Vortex valve outlet gate control - Google Patents

Abstract

A vortex valve assembly in which pressure within the vortex chamber provides a switching function for automated opening of a gate 14 to increase the size of the outlet 6 in event of blockage. The pressure rise at outlet 9 in the volute due to collapse of the vortex on blockage is used to provide a mechanical displacement to operate the gate. An energy storage system (23 Figs 9,10) may be used to delay opening and prevent partial gate oscillation for a single blockage event. An enlarged outlet may also be provided for low flow conditions and may be maintained up to a predetermined head external to the assembly. Pressure is used to provide mechanical displacement via flexible membranes 10, 12, bellows and/or piston assemblies via a fluid column 11. Springs or head may be used to provide bias to oppose the displacement.

Description

Vortex Valve SYstem This invention relates to flow rate control using

vortex valves and to mechanisms for preventing or relieving blockages within vortex controlled fluid flow systems.

Vortex valves are used to control liquid flow where the nature of the flow requires maintenance of a relatively large orifice but the flow requires restriction. Such environments are found in combined sewerage systems, where both waste water lo and storm water are collected and pass to a pipe system, and also in storm water systems. Debris of various sizes, density and fibrous content is present in the flow and therefore to prevent blockages a large orifice is desirable. However, in the event of high loading, such as may occur after or during a storm, the entry of flow into the pipe system has to be retarded in order to prevent risk of overload and back pressure.

A typical vortex valve has a chamber that is conical or cylindrical, and fluid is introduced at a tangent to the circular wall so that the liquid is set in rotary motion.

At a predetermined flow rate or head, which depends upon the design of the system, the flow establishes a vortex that discharges flow at a predetermined rate.

In general flow Q through an aperture or orifice takes the form of Q = Cd AV where Cd is a coefficient of discharge provided by the orifice, A is the diameter of the orifice, and V is the velocity provided by the operating head (V = i/ (2gH) ).

H is the applied head of water. - 2

From this it will be appreciated that for a given flow and head, the diameter of the orifice can be larger if the discharge coefficient is low. Vortex valves with Cal near 0.12 have been achieved. This compares favourably with a sharp edged orifice value of 0.62, allowing a vortex flow control to operate with an outlet orifice some fivetimes larger.

However, there are still numerous instances where the outlet is subject to blockage or other circumstances make bypass routes desirable.

lo The present invention is directed towards providing a system for controlling low flows via a vortex valve with a bypass or overload path that is controlled in response to vortex conditions.

According to the invention there is provided a vortex valve assembly comprising a Is vortex chamber with an inlet and an outlet and means responsive to a pressure increase within the vortex chamber to provide a switching function.

The invention also provides a vortex valve assembly including a movable gate and in which the gate is biased to an open position establishing a large outlet, and in which pressure head is applied against the bias such that at a predetermined pressure the gate is closed to provide a reduced outlet aperture size.

The assembly may also include a vortex valve assembly in which the gate is carried by a gate frame and the gate frame is biased to an open position and closed to a position that puts the gate in position in the outlet at a predetermined head external of the assembly, and in which the gate has separate biasing arrangements.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a graph showing flow curves; 3 Figure 2 is a schematic diagram of a first embodiment of the invention on a conical vortex valve; Figure 3 is a schematic diagram of a second embodiment of the invention; Figure 4 is a perspective view of a conical vortex valve from above, illustrating flow; Figure 5 is a schematic diagram from one side of a cylindrical vortex valve, lo illustrating flow; Figure 6 is a schematic diagram of a standard vortex valve showing enlarged aperture and gate according to the invention; Figure 7 shows the valve of Figure 5 viewed from the side at right angles to the I Figure 6 view; Figure 8 is a schematic illustration of a gate which may be used in any of the embodiments of the invention.

Figure 9 shows schematically an embodiment of the invention incorporating an energy storage device/delay; Figure 10 shows an embodiment of the energy storage device/delay, and Figure 11 shows an embodiment incorporating a bias arrangement for a gate responsive to external head.

Figure 1 shows the different shapes of typical flow curves of flow rate Q versus head of pressure H for a relatively large orifice, curve 1, a relative small orifice, curve 2, and a vortex valve, curve 3.

The orifice curves follow a parabola, while the vortex curve is composed of two parabolic curves connected by a kick-back. This kick-back occurs as the vortex forms within the volute. Prior to vortex formation the valve curve follows the curve of the larger orifice 1, and after initiation of the vortex it follows the curve of the s smaller orifice.

Figures 4 and 5 show two known types of vortex valves. Figure 4 shows a conical valve viewed from above. The valve comprises a cone with an inlet 5 at its wide end and an outlet 6 at its apex. In use, as more clearly shown in Figure 2, the inlet lo and outlet are positioned generally in a horizontal or near horizontal alignment which will provide a smooth fluid path, i.e. no step in the fluid run as seen from inlet and outlet.

It will be seen from the arrows of Figure 4 that rotational momentum is imparted to the fluid by introduction at a tangent to the circular wall of the cone. At the critical pressure, or head, which depends on the geometry of the valve, a vortex establishes, with the core of the vortex lying along the axis of the cone, which is generally between the dotted lines 7 shown in Figure 2.

The other type of vortex valve, called a "cylindrical" valve is shown in Figure 5, viewed from one side. This comprises a short cylindrical or disc shaped housing with flow being introduced tangentially through inlet 5 and discharging through an outlet in the centre of one of the discs. It will be appreciated that with this valve, inlet and outlet are not on the same general level. When the vortex establishes, again the core is in line with the outlet and extends between the centre points of the disc walls, i.e. along the axis of the disc/cylinder.

These descriptions of vortex valves are general, and may be modified, for example in the angle at which the flow is introduced, for particular purposes.

Turning now to Figure 2 this shows an embodiment of the invention on a conical vortex valve 4. As described above, the valve is of a conical shape with an inlet 5 - 5 for liquid at the lower placed side of the wide end of the cone and an outlet 6 at the apex. It will be realised that the direction of the outlet is generally at right angles to the inlet which is a feature of vortex valves. The change in direction may not always be 90 , but incorporates a change from a tangential or near tangential inlet to a substantially axial outlet brought about by the establishment and geometry of the vortex. Additional tilts to inlet or outlet may be provided for particular purposes.

Likewise, the inlet opening may incorporate other features to assist in flow control.

The mouth (wide end) of the cone is covered by a plate 8 with an aperture 9. An lo elastic flexible membrane 10 seals over the aperture. The membrane may lie substantially flat, or as illustrated project outwardly. A pipe 11 is also attached over the aperture, and the membrane also seals the end of the pipe.

Pipe 11 is filled with a fluid (gas or liquid), preferably a liquid, and at its second end it terminates with another elastic flexible membrane 12, that bears against a piston 13. When pressure at the centre of the volute chamber increases, which occurs if the vortex breaks down as a result of a blockage of the outlet 6, the membrane 8 expands, ballooning outwardly into the fluid in pipe 11, thereby causing a corresponding ballooning and displacement of membrane 12. Membrane 12 bears against piston 13 which provides the mechanical displacement to open a bypass or other form of gate 14. It will be appreciated that the pressure in the volute chamber is essentially being used as a switch, to utilise the pressure in the volute to operate the bypass or gate 14. The switching function could be applied in other ways, even for example as a trigger for electrical or other operation of the gate.

A vortex when maintained is capable of withstanding very large increases of pressure head without exerting pressure on the membrane 10. Likewise reduction in flow to below vortex formation level does not produce an increase in volute so pressure. Therefore, as stated above, a pressure increase only arises from a blockage within or after the volute, usually at the outlet orifice. A temporary external bypass can be operated to allow servicing of the blocked orifice, but automated unblocking is preferred. Hence in a preferred aspect of the present invention, the outlet 6 is modified to be of variable size and when piston 13 is operated, the outlet is enlarged. A convenient way to provide this is for the outlet to be in the form of an enlarged aperture, stopped down by a gate with an aperture of the design size.

s When blockage occurs the gate is lifted, thereby opening up the fluid path to the enlarged aperture, both relieving the pressure and the blockage.

In Figure 3 a second embodiment is shown in which the piston 13 is placed in contact with the first flexible, membrane 10 and a pivoted lever 23 and sheathed lo cable 22 are provided as the link for raising gate 14.

Another embodiment of a vortex valve according to the invention is shown in Figure 6. The valve comprises a so called cylindrical vortex chamber having a generally disc shaped or short cylindrical housing with end walls or discs connected by a circumferential wall 20 with a tangential inlet opening 5. As before, the inlet opening may incorporate features that assist in flow control, in addition to the features described in the context of the present invention. The outlet of the vortex valve is a central opening 6 in one of the disc walls of the housing, again such that the flow is usually discharged at right angles to the inlet flow.

Comparing Figure 6 with Figure 5 it will be seen that the outlet 6 has been enlarged from an arched outlet to (as shown) a larger rectangular outlet. Gate 14 is shown in a raised position, but when lowered it will stop down aperture 6 to the general size of the aperture shown in Figure 5. The gate and aperture of the Figure 2 2s embodiment may be similarly arranged. Although the enlarged aperture is shown as a rectangle, it may be any shape, and in general it may be preferred to have rounded corners In the disc wall that is opposite to the outlet seen in Figure 7, there is an opening that is sealed by an elastic, flexible membrane 10 which, as in the first embodiment, is arranged to expand when pressurized into a pipe 11, and which operates to raise piston 13, or otherwise provide a switch function, as previously described on vortex breakdown. Connection 21 schematically represents a linkage from the piston to the gate.

Figure 8 shows schematically a gate 14 suitable for either embodiment that can be s raised to enlarge the aperture to the larger size shown in dotted outline 15. When lowered, the gate seals against the volute and provides an orifice 16 appropriate for the design of the volute. The provision of gates of this type also provides opportunity to provide a different orifice size, and therefore Qv, for the vortex operation by changing the gate rather than the entire volute.

It is well known to use gates to control flow in the water and sewerage industry.

Usually, the gates are required to be watertight However, as this is an apertured gate the requirement for watertightness is reduced or eliminated as leakage is acceptable and will be taken up in the overall flow efficiency of plus or minus 5 to 7%. The design priority for the gate is to minimize friction and keep as much metalwork as possible away from the outlet to prevent ragging.

In the arrangements described, it is possible for the gate to open a small amount as soon as the piston moves, which may result in a partial relief of the blockage and temporary re-establishment of the vortex. However, further blockage may then occur and undesirable repeated partial opening and closing of the gate result from a single blockage event. Thus to prevent this an energy storage system may be interposed between the piston and gate opening link. The energy storage system absorbs the piston motion until a level at which the movement is sufficient to open Is the gate fully.

Figure 9 shows schematically an energy storage device 23 between piston 13 and cable 22. A suitable form of device may be a torsion spring rotated by a rack located on the top of the piston and a pinion attached to the spring. A ratchet and pawl assembly can provide a release mechanism to allow full raising of the gate a short time (and movement) interval after onset of piston motion. - 8

Other forms of delay and energy storage may be used. Further detail of a rack, spring and pinion device is shown in Figure 10.

In Figure 10, as the piston 13 moves up or down, as shown by the arrows, a rack 24 s is similarly moved. So as the piston moves upwards at the onset of a blockage and vortex breakdown, rack 24 moves up rotating pinion 30 and tensioning spring 25.

A ratchet 26 is attached to the spring and the ratchet is restrained by a pawl 27.

Extending from the pawl is a release member 28 which, after sufficient upward movement of piston 13, is engaged by a co-operating release member 29, which 0 releases the pawl and allows the spring tension to be released by rotation of the ratchet and cable drum 31 which is mounted on a common rotatable shaft. Rotation of the cable drum lifts the gate.

The movement of the rack will generally be two to three times the distance that the gate moves for full opening and it is convenient if it is arranged that the cable drum rotates approximately one revolution which prevents potential overlap of the cable.

In a further modification of the invention, in addition to opening to relieve blockage or surplus flow, the gate may also be opened at low flows which reduces risk of blockage and improves the low flow characteristic. The pressure head may be used to do this.

The pressure head can be regarded as having two zones. A low pressure, low flow zone when the vortex does not form and the flow passes simply through the valve.

Is Under these conditions the gate can be open.

The second pressure zone relates to the pressure head under which the vortex forms and commences retarding the fluid This will vary dependent upon the design of a particular volute, but at the operational pressure the gate is closed so that the orifice size for which the volute is designed is present. At pressure heads above the vortex formation head, the vortex remains established and retards fluid holding it back in the system, and generally while the vortex is maintained the gate remains closed. - 9 -

The pressure head of these pressure zones can be applied to automatically open or close the gate against a mechanical bias on the gate.

s The mechanical bias on the gate, which may be provided by a spring for example, holds the gate open and the pressure head is applied against the bias, with the bias designed so that when near the operational pressure is reached, the gate is closed.

The gate remains closed irrespective of pressure head, but is openable by the piston 13 in the event of vortex breakdown.

There may be circumstances where it is desirable to keep the gate open after vortex formation until a predetermined head external to the device is reached. The predetermined head is selected by the mechanical bias on the gate.

Figure 11 shows an arrangement in which the mechanical bias on the gate may be derived from the external head. The gate 14 is carried in a movable gate frame 33.

Gate 14 operates as previously described within the gate frame, but the gate frame complete with gate 14 is held open until the external head (arrow 34 acting on membrane 35) reaches the predetermined head. It will be appreciated this may be regarded as operating the volute with, initially, a larger design outlet aperture.

Consideration may also be given to the form of the orifice and its location on the gate as differing flow characteristic may result from whether the orifice is central to the enlarged aperture or vertically offset so that it is 'eclipsed' at an earlier or later Is stage of gate movement.

The use of elastic, flexible membranes enables much of the pipework, and in particular the piston or other moving parts, to be isolated from the environment of the liquid, thereby keeping friction levels low and eliminating risk of fouling and so jamming. -

The flexible membrane 10, as shown in Figure 2, may be replaced by other mechanisms providing flexible expansion such as a bellows. These arrangements may not lie directly at the aperture 9 but may communicate with it via a pipe or other conduit. One example of this is shown in Figure 9.

Claims (16)

1. A vortex valve assembly comprising a vortex chamber with an inlet and an outlet and means responsive to a pressure increase within the vortex chamber to provide a switching function.

2 A vortex valve assembly according to claim 1 in which the means responsive to a pressure increase is responsive to pressure at the location of the lo centre of the vortex.

3 A vortex valve assembly according to claim 1 or claim 2 in which the switching function comprises moving a gate to increase the size of the outlet.

4 A vortex valve assembly according to any preceding claim in which the means responsive to a pressure increase comprises an aperture sealed by an elastic membrane or bellows.

5. A vortex valve assembly according to claim 4 in which the elastic membrane also seals a first end of a fluid filled pipe so that pressure increase in the vortex chamber expands the membrane into the pipe and displaces the fluid.

6. A vortex valve assembly according to claim 5 in which a second elastic membrane seals the second end of the pipe and when the fluid displaces it expands the elastic membrane at the second end of the pipe to provide a mechanical displacement for the switching function.

7 A vortex valve assembly according to claim 6 in which the sealed aperture is opposite the outlet. - 12

8. A vortex valve assembly according to claim 7 in which the outlet and sealed aperture lie substantially at opposite ends of the axis of symmetry of the vortex chamber.

9. A vortex valve assembly according to claim 4 in which expansion of the elastic membrane in response to pressure increase moves a piston.

10. A vortex valve assembly according to claim 9 in which the piston is coupled to a cable for moving a gate to increase the size of the outlet.

11 A vortex valve according to claim 9 in which an element between the piston and gate delays opening of the gate until the piston has moved a predetermined distance.

12. A vortex valve assembly according to any preceding claim in which the valve is a conical valve.

13. A vortex valve assembly according to any of claims 1 to 12 in which the I valve is a cylindrical valve.

14. A vortex valve assembly according to any preceding claim including a movable gate and in which the gate is biased to an open position establishing a large outlet, and in which pressure head is applied against the bias such that at a predetermined pressure the gate is closed to provide a reduced outlet aperture size.

15. A vortex valve assembly according to claim 14 in which the gate is carried by a gate frame and the gate frame is biased to an open position and closed to a position that puts the gate in position in the outlet at a predetermined head external of the assembly, and in which the gate has separate biasing arrangements.

16. A vortex valve assembly substantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.