WO2001077558A1

WO2001077558A1 - Pressure relief valves

Info

Publication number: WO2001077558A1
Application number: PCT/AU2001/000404
Authority: WO
Inventors: Simon Robert Karpeles
Original assignee: Transfield Pty Ltd
Priority date: 2000-04-10
Filing date: 2001-04-10
Publication date: 2001-10-18
Also published as: AUPQ679800A0

Abstract

A pressure relief valve (1) including a valve body (2) having a generally horizontally oriented valve seat (3), a substantially planar valve member (4) adapted normally to rest under its own weight in a closed position on the valve seat (3), the valve member (4) thereby defining a first region (10) below the valve seat (3) and a second region (11) above the valve seat (3). Guide means (12) are disposed peripherally around the valve member (4) to permit a limited degree of generally vertical displacement of the valve member (4) away from the valve seat (3) into an open position while substantially restricting horizontal displacement, the valve being operable in use such that a transient positive fluid pressure in the first region (10) relative to the second region (11) above a predetermined threshold level operates to lift the valve member (4) off the seat (3) and allow fluid to flow from the first region (10) past the valve member (4) into the second region (11), thereby tending automatically to reduce the relative pressure differential.

Description

- 2 - vents the pressurised fluid through the port, to atmosphere, or an ambient environment. When the pressure differential drops back to the threshold level, the valve is returned to the closed position by the spring. This relief mechanism thereby operates automatically to prevent pressure from reaching dangerous levels which could otherwise rupture the associated vessel, pipework, or valve mechanism.

A major shortcoming with valves of this type, particularly when used in corrosive atmospheres or environments, is that they involve a number of intricately interconnected component parts which must be formed from relatively expensive materials such as metal alloys and fabricated within relatively tight tolerances. In addition to the materials themselves, the time involved in manufacture and assembly add considerably to the overall cost of valves of this type. This renders them commercially unviable in some situations, particularly in larger scale applications. On the other hand, more cost effective materials such as fibre reinforced plastics (FRPs) and other composites are difficult to fabricate to the required dimensional tolerances. A further issue with valves of this type is that, because of the number of moving parts and the relatively close operating tolerances, reliability is often a problem. Periodic maintenance is also required to ensure that adjacent parts mate correctly, and that the valve provides an effective seal when closed. In addition to the direct cost involved, maintenance of this type, whether scheduled or imposed by component failures, can involve significant plant downtime.

Other problems with known valves arise by virtue of the fact that because the operational clearances are relatively small, the valves can become clogged or jammed relatively easily by slime or particulate debris, again requiring maintenance and downtime to clear. Furthermore, when manufactured from conventional materials, such - 3 - valves can also be subject to rapid wear and/or high failure rates in harsh abrasive or corrosive environments.

Yet another problem arises in some situations due to the structure of the poppet valve, guide and spring. This arrangement can inherently restrict the maximum extent to which the valve can open, which in turn inherently limits the maximum flow rate through the valve. The valve stem, guide and spring can also in certain circumstances constrict the outlet port behind the valve head, further restricting the maximum flow rate. In situations where pressure changes occur rapidly or when the magnitude of the fluctuations is high, this inherent limitation to flow rate may impede the ability of the valve to prevent pressure differentials from exceeding critical values.

The foregoing description of the prior art is provided so that the present invention may be more fully understood and appreciated in its technical context and its significance more fully appreciated. Unless clearly indicated to the contrary, however, this discussion is not, and should not be interpreted as, an express or implied admission that any of the prior art referred to is widely known or forms part of common general knowledge in the field.

It is an object of the present invention to overcome or ameliorate one or more of these disadvantages of the prior art, or at least to provide a useful alternative. DISCLOSURE OF THE INVENTION Accordingly, the invention provides a pressure relief valve including a valve body having a generally horizontally oriented valve seat, a substantially planar valve member adapted normally to rest under its own weight in a closed position on the valve seat, the valve member thereby defining a first region below the valve seat and a second region above the valve seat, and guide means disposed peripherally around the valve member to permit a limited degree of generally vertical displacement of the valve - 4 - member away from the valve seat into an open position while substantially restricting horizontal displacement, the valve being operable in use such that a transient positive fluid pressure in the first region relative to the second region above a predetermined threshold level operates to lift the valve member off the seat and allow fluid to flow from the first region past the valve member into the second region, thereby tending automatically to reduce the relative pressure differential.

Preferably, the valve member is generally flat, with its upper and lower surfaces being substantially planar. In the preferred embodiment, the valve member conveniently takes the form of a substantially flat circular disc or plate. It will be appreciated, however, that the valve member could be any suitable simple or compound shape. In particular, it may be curved, or even spherical.

Preferably, the valve includes abutment means disposed to limit the maximum extent of vertical displacement of the valve member away from the valve seat. The abutment means preferably include a top plate fixedly attached to the valve body, at a predetermined vertical spacing from the valve seat, this spacing corresponding to the extent of maximum vertical displacement of the valve member away from the seat. In the preferred embodiment, the top plate is positioned closely adjacent the valve seat such that limited vertical movement brings the valve member into close fitting, surface to surface abutment with the underside of the top plate. The spacing of the abutment means is preferably predetermined so as to prevent the valve member from rotating about an horizontal axis or "flipping" within the valve body.

Preferably, the top plate is spaced apart from the valve seat by spacing elements. In the preferred embodiment, the spacing elements comprise an array of discrete guide rods disposed around the outer periphery of the valve member. - 5 -

In one preferred embodiment, the valve is configured to function as an overpressure relief valve, with the first region in fluid communication with a pressure vessel, and the second region in fluid communication with a surrounding atmosphere to allow fluid transfer unidirectionally from the vessel to the atmosphere, when the relative pressure differential exceeds the predetermined threshold level. In this embodiment, the spacing elements preferably also act as the guide means to restrict horizontal displacement of the valve member.

In an alternative embodiment, the valve is configured to function as a vacuum or under-pressure relief valve, with the first region in fluid communication with a surrounding atmosphere via an inlet duct, and the second region in fluid communication with a pressure vessel, to allow fluid transfer unidirectionally from the atmosphere to the vessel. In this embodiment, the guide means preferably take the form of a plurality of longitudinally oriented guide plates extending radially inwardly from the valve body adjacent the valve member. In a further preferred variation, the invention provides a combined pressure and vacuum relief valve assembly including a first valve configured to operate as a pressure relief valve, and a second valve configured to operate as a vacuum relief valve, wherein the first region of the first valve is connected in fluid communication with the second region of the second valve, wherein the second region of the first valve is connected to atmosphere and the first region of the second valve is likewise connected to atmosphere, and wherein both the first and second valves are effectively housed within an integral unitary valve body.

In preferred embodiments of the invention, the valve body is formed from fibre reinforced plastic (FRP), and the valve member is formed as a fibre reinforced plastic disc. - 6 -

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a cross sectional side elevation showing a first embodiment of the invention configured as an over-pressure relief valve;

Figure 2 is a cross sectional side elevation showing a second embodiment of the invention configured as a vacuum or under-pressure relief valve; and

Figure 3 is a cross sectional side elevation showing a third embodiment of the invention, configured as a combined pressure and vacuum relief valve. PREFERRED EMBODIMENT OF THE INVENTION

Referring initially to Figure 1, the invention provides a pressure relief valve 1 including a valve body 2. The valve body incorporates a horizontally oriented valve seat 3. A substantially planar valve member 4 is adapted normally to rest under its own weight in a closed position on the valve seat. The valve member takes the form of a substantially flat circular disc, having planar upper and lower surfaces. The valve member effectively divides the valve body internally into a first region 10 disposed below the valve seat, and a second region 11 above the valve seat.

The valve further includes guide means 12 disposed peripherally around the valve member. These guide means permit a limited degree of generally vertical displacement of the valve member away from the valve seat into an open position, while substantially restricting lateral or horizontal displacement.

The valve further includes abutment means disposed to limit the maximum extent of vertical displacement of the valve member away from the valve seat. The abutment means take the form of a top plate 15 fixedly attached to the body, at a predetermined vertical spacing from the valve seat. This spacing corresponds to the extent of maximum - 7 - vertical displacement of the valve member away from the seat, and is limited to prevent the valve member from flipping or spinning about an horizontal axis. Ideally, the top plate is positioned closely adjacent the valve seat such that limited vertical movement of the valve member brings it into close fitting, surface to surface abutment with the underside of the top plate. The vertical clearance between the valve seat and the top plate will be determined partly by design parameters, having regard to the expected maximum pressure differentials, and flow rates through the valve.

The top plate is spaced apart from the valve seat by a circular array of discrete guide rods 17 disposed around the outer periphery of the valve member. In the embodiment shown in Figure 1, these guide rods 17 also function as the guide means 12, restricting horizontal displacement of the valve member. It will be appreciated, however, that these functional elements need not be integral.

The valve is operable in use such that a transient positive fluid pressure in the first region, relative to the second region, above a predetermined threshold level operates to lift the valve member off the seat. This allows fluid to flow from the first region past the valve member into the second region, thereby tending automatically to reduce the relative pressure differential. When the pressure differential drops below the threshold level, the valve member returns to its seat under the operation of gravity, to close the valve once again. Importantly, it will be noted that in this arrangement, the only moving part is the valve member itself, which fits within loose tolerances between the guide rods 17. In particular, it will be noted that there is no valve spring, no axial valve stem, and no tubular valve guide slidably supporting the valve stem.

The valve of Figure 1 is configured to operate as an over-pressure relief valve. In this configuration, the first region 10 is in fluid communication with a pressure vessel, and the second region 11 vents to atmosphere. This allows fluid, normally gas, to - 8 - transfer unidirectionally from the vessel to atmosphere, when the pressure exceeds the predetermined threshold level. This level will be a function of the effective size and weight of the valve member, which is configured according to the design parameters of the valve. Obviously, valve members formed from dense materials such as cast iron will inherently dictate higher relief pressures than relatively lighter materials such as aluminium.

The valve body itself is preferably formed from fibre reinforced plastic (FRP), and ideally from fibreglass. This enables the valve to be produced in large sizes, and in configurations allowing relatively high volumetric flow rates, in a unit which is comparatively light in weight and inexpensive to produce. The cost savings arise partly because inexpensive materials can be used, partly because the higher capacity means that relatively fewer valves are required for a given application, and partly because manufacturing and operational tolerances can be relaxed without impeding the basic functionality and performance of the valve. A second embodiment is shown in Figure 2, which illustrates a valve 20 according to the invention, configured to provide vacuum or under-pressure relief. In this embodiment, corresponding features are denoted by corresponding reference numerals. It will be appreciated, however, that the guide means 12 take the form of axially extending, inwardly depending longitudinal guide plates 22, which perform essentially the same function as guide rods 17, in terms of permitting limited vertical movement of the valve member, while restricting horizontal displacement. In this case, however, the top plate 15 bolts directly to the top flange of the valve body, so that separate spacing elements are not required.

In this configuration, the first region 10 is in fluid communication with atmosphere via inlet duct 23, and the second region 11 is in fluid communication with a pressure - 9 - vessel, typically a vacuum chamber. This allows unidirectional fluid transfer from atmosphere into the vessel, when a predetermined negative pressure differential across the valve member is exceeded.

Figure 3 shows a third embodiment of the invention, in which first and second valves, corresponding to those illustrated in Figures 1 and 2 respectively, are combined in an integral over and under-pressure relief valve assembly 30, within a unitary valve body. Again, corresponding features are denoted by like reference numerals. Thus, in this case, the unitary valve body 2 incorporates an over-pressure relief valve 1, and an under-pressure relief valve 20. In the combined valve 30, the first region 10 of the over- pressure relief valve is in direct fluid communication with the second region of the under-pressure relief valve 20, both of which are in fluid communication with the pressure vessel by means of the main body and the mounting flange 35. The second region 11 of the over-pressure valve, and the first region 10 of the under-pressure valve respectively vent to atmosphere. In this configuration, if the positive pressure in the vessel exceeds the threshold level for the over-pressure valve, this valve opens to vent fluid to atmosphere radially, past the guide rods 17. During this process, the second valve remains positively closed by virtue of the fact that the pressure on the upper surface of the valve member, corresponding to the pressure in the vessel, exceeds ambient pressure. On the other hand, if the pressure in the vessel drops below the threshold level for the under-pressure valve 20, this valve opens, thereby permitting fluid to flow into the valve body from atmosphere, through the inlet duct 23. During this process, the over-pressure valve remains positively closed, because the ambient pressure on the upper surface of the valve member exceeds the pressure within the valve body and the vessel. It will be - 10 - appreciated that this embodiment of the invention is particularly useful in applications where pressures may fluctuate both positively and negatively.

In the preferred embodiments of the invention, the volumetric capacity of the relief valve is preferably up to around 2m³/second, and most preferably up to around 4m³/second, with an operating pressure ranging from -10.Okpa to +10.Okpa, and a relative threshold actuation pressure of around 0.5kpa. It will be appreciated, however, that the precise dimensions and operating parameters can be tailored to suit the particular application, operating conditions, and design constraints.

It has been found that valves according to the present invention are particularly well adapted for use in sewerage treatment plants, where sewerage is biochemically decomposed within closed vessels, to contain unpleasant odours, and minimise the potential for contamination of the surrounding environment. Such valves are typically large in size, so as to safely accommodate relatively high transient peak pressures and flow rates. It will be appreciated, however, that the valves are equally well suited to a wide variety of other applications.

In terms of advantages, it has been found that valves according to the present invention can be manufactured in a wide variety of sizes, shapes and configurations, from relatively inexpensive materials such as plastics, FRPs as well as metals. Substantial cost savings are realised because such materials can be used, the shapes are less intricate, there are fewer moving parts, and the design is inherently less sensitive to manufacturing tolerances, as compared with conventional valve designs. The substantial reductions in manufacturing cost also enable substantially larger valves to be produced in a cost effective manner. This often enables a smaller number of larger valves to be used in a given application, which in turn leads to further overall cost reductions. Another significant advantage provided by the present invention is that because of the - 11 - relatively small number of moving parts, and the absence of close tolerances and clearances between the parts, the valve is less prone to clogging and jamming, which implies improved reliability. The smaller number of moving parts also minimises the risk of failure, which again enhances reliability. In addition, because the valves can be designed to provide relatively high flow rates, the safety risk of the valve's capacity being exceeded by transient pressure differentials is reduced. Because of the relatively open tolerances, the resistance of the valve to abrasive wear is also improved. A further secondary benefit is that because of the simplicity of the overall valve design which enables it to be manufactured in a variety of different materials, the materials can be selected to provide optimum resistance to corrosion in harsh chemical environments. In all of these respects, the invention represents a commercially significant improvement over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms .

Claims

- 12 -CLAIMS:-

1. A pressure relief valve including a valve body having a generally horizontally oriented valve seat, a substantially planar valve member adapted normally to rest under its own weight in a closed position on the valve seat, the valve member thereby defining a first region below the valve seat and a second region above the valve seat, and guide means disposed peripherally around the valve member to permit a limited degree of generally vertical displacement of the valve member away from the valve seat into an open position while substantially restricting horizontal displacement, the valve being operable in use such that a transient positive fluid pressure in the first region relative to the second region above a predetermined threshold level operates to lift the valve member off the seat and allow fluid to flow from the first region past the valve member into the second region, thereby tending automatically to reduce the relative pressure differential.

2. A pressure relief valve according to claim 1, wherein the valve member is generally flat.

3. A pressure relief valve according to claim 1 or 2, wherein upper and lower surfaces of the valve member are substantially planar.

4. A pressure relief valve according to any one of the preceding claims, wherein the valve member comprises a generally circular disc or plate.

5. A pressure relief valve according to any one of the preceding claims, further including abutment means disposed to limit the maximum extent of displacement of the valve member in the vertical direction away from the valve seat.

6. A pressure relief valve according to claim 5, wherein the abutment means include a top plate attached to the valve body, at a predetermined vertical spacing from the valve - 13 - seat, the spacing corresponding to the extent of maximum vertical displacement of the valve member away from the seat.

7. A pressure relief valve according to claim 6, wherein the top plate is positioned closely adjacent the valve seat such that the limited degree of permitted vertical movement brings the valve member into close fitting surface to surface abutment with an underside of the top plate.

8. A pressure relief valve according to claim 7, wherein the spacing of the abutment means is predetermined so as to prevent the valve member from fully rotating about an horizontal axis within the valve body.

9. A pressure relief valve according to claim 8 wherein the top plate is spaced apart from the valve seat by spacing elements.

10. A pressure relief valve according to claim 9, wherein the spacing elements comprise an array of discrete guide rods disposed around an outer periphery of the valve member.

11. A pressure relief valve according to claim 10, wherein the spacing elements also function as the guide means to restrict substantial horizontal displacement of the valve member.

12. A pressure relief valve according to any one of the preceding claims, wherein the valve is configured to function as an over-pressure relief valve, with the first region in fluid communication with a pressure vessel, and the second region in fluid communication with a surrounding atmosphere, thereby to allow unidirectional fluid transfer from the pressure vessel to the atmosphere, when the relative differential pressure exceeds the predetermined threshold level.

13. A pressure relief valve according to any one of claims 1 to 9, wherein the valve is configured to function as an under-pressure relief valve, with the first region in fluid - 14 - communication with a surrounding atmosphere via an inlet duct, and the second region in fluid communication with a pressure vessel, thereby to allow unidirectional fluid transfer from the atmosphere into the pressure vessel when the relative differential pressure exceeds the predetermined threshold level.

14. A pressure relief valve according to claim 13, wherein the guide means comprise a plurality of elongate axially oriented guide plates extending radially inwardly from the valve body adjacent the valve member.

15. A combined pressure and vacuum relief valve assembly, including a first valve according to claim 12 configured to operate as a pressure relief valve, and a second valve according to claim 13 configured to operate as a vacuum relief valve, wherein the first region of the first valve is connected in fluid communication with the second region of the second valve, wherein the second region of the first valve and the first region of the second valve are connected to atmosphere, and wherein both the first and second valves are effectively housed within an integrated valve body.

16. A pressure relief valve according to any one of the preceding claims, wherein the valve body is formed from a fibre-reinforced plastics (FRP) material.

17. A pressure relief valve according to any one of the preceding claims, wherein the valve member is formed from a fibre-reinforced plastics (FRP) material.

18. A pressure relief valve according to any one of the preceding claims, wherein the valve member is formed at least partially from metal.

19. A pressure relief valve according to any one of the preceding claims, having a volumetric capacity of up to around 2m³/second.

20. A pressure relief valve according to any one of the preceding claims, having a volumetric capacity of up to around 4m³/second. - 15 -

21. A pressure relief valve according to any one of the preceding claims, having a pressure capacity ranging from -lO.Okpa to -i-lO.Okpa.

22. A pressure relief valve according to any one of the preceding claims, wherein the threshold pressure differential is approximately 0.5kpa.

23. A pressure relief valve substantially as herein described with reference to any one of the embodiments of the invention as illustrated in the accompanying drawings.