WO2007052047A1

WO2007052047A1 - Safety valve

Info

Publication number: WO2007052047A1
Application number: PCT/GB2006/004115
Authority: WO
Inventors: Stuart Morrison
Original assignee: Henry Technologies
Priority date: 2005-11-03
Filing date: 2006-11-03
Publication date: 2007-05-10
Also published as: GB0522411D0

Abstract

There is described a safety valve control mechanism wherein a safety valve (10) controls and/or limits compression of valve springs (20) . A mechanical stop (16) is used to control and/or limit spring deflection.

Description

SAFETY VALVE

FIELD OF THE INVENTION

The present invention relates to controlling and/or limiting compression of valve springs. In particular, the present invention relates to the provision of a mechanical stop (i.e. a spring stop) capable of controlling and/or limiting spring deflection.

BACKGROUND OF THE INVENTION

It is common practice for safety valve standards to require that a spring must not be over-compressed. Usually, the allowable deflection (i.e. travel) is required to be restricted to about 80% of the total spring travel. It is therefore usual that a spring has about an extra 20% travel before being fully compressed into a solid form.

However, there exists a problem in the art of controlling the deflection of springs to optimise the operation of valve springs, and to prevent springs from being over-compressed, which will result in deterioration of valve performance, reliability and operational lifetime.

It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.

It is a further object of at least one aspect of the present invention to provide safety valve apparatus capable of controlling the compression of valve springs.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a valve spring arrangement comprising a mechanical stop, said mechanical stop capable of controlling and/or limiting the compression of the valve spring.

Typically, the mechanical stop may function as a spring stop and may be of any suitable form which may be adapted to control and/or limit the compression of the valve spring.

Preferably, the spring allows sufficient movement (i.e. compression) to counter the forces during pressure setting. Additionally, the spring may allow additional travel to allow a valve piston (or plunger) to move away from a seat when a valve opens (i.e. pops) .

There may be one, at least two or more, or a plurality of springs in the valve spring arrangement. In the event that there are two or more springs, the springs may be connected in series with one another. Therefore, two shorter springs may be stacked together in series, instead of using a single longer spring. Any suitable form of connection means may be used.

The valve spring arrangement may therefore be adapted to allow a piston to move away from a seat by a suitable pre-determined distance, to allow flow through the valve. The actual distance that the piston moves away from a valve seat, dictates the flow capacity of the valve. Preferably, the maximum spring travel allowed may be about 10% - 90%, 20% - 80%, 30% - 60%, a maximum of about 50% or a maximum of about 80% of the total travel. This facility helps to prevent over-compression of the spring. Due to these parameters, a valve provider is usually forced to have a number of different spring designs to accommodate a range of valve pressure settings. The present invention overcomes this problem.

As set out in the present invention, there is provided a mechanical stop which has a function of acting as a "spring stop", or a "bump stop". Any part such as an end member on the mechanical stop may function to prevent movement or restrict movement of the valve spring.

The mechanical stop may be adapted to be snugly received within the valve spring. The length of the mechanical stop, is dependent upon the specific design requirements such as the pressure set value along with the required amount of travel to allow sufficient piston lift when the valve is in the open position.

Preferably, the mechanical stop length may be adapted to restrict the amount of spring travel, such as to about 20% - 80%, or a maximum of about 80% of the total travel of the spring.

Conveniently, the mechanical stop may be tubular- like such as in a substantially cylindrical form adapted to be received within the inside perimeter of the spring.

The mechanical stop may also be adapted to be telescopic in form, so that the length of the mechanical stop may be changed and varied for a variety of different spring requirements . The required length of the mechanical stop may then be selected, and once the required length is obtained, the length of the mechanical stop locked in position.

The mechanical stop may be made from any suitable material, such as any plastics, polymeric material, composite, or metal/alloy material.

At the end opposite to that of the valve seat, the mechanical stop may be adapted to be received within a receiving member such as an adjusting gland. The receiving member may be moved up and down within a chamber of the safety valve to provide different valve arrangements and pressure settings. Typically, the end of the mechanical stop intended to be received in the receiving member may be substantially conical in shape, and may have a protruding member to be received within a recess in the receiving member. The mechanical stop may be positioned or located within the receiving member.

In certain embodiments, a spacer or washer may be located on a circumferential edge of the spring stop. The purpose of the spacer or washer may be to help to align the spring stop into the correct alignment such as being substantially vertical. This may help so that when the spring stop makes contact with the piston, the resulting force may be more uniform and/or centralised. In the event that the spring stop just sits on the spring directly, some misalignment may occur from manufacturing intolerances of the spring coils.

In alternative embodiments, the piston and spring stop may have central passages. This may allow the flow of liquid and/or gas through the piston and spring stop.

The present invention therefore provides the advantageous feature of controlling the compression of a spring. By limiting piston and spring travel by means of the described spring stop arrangement according to the present invention, a one piece valve body design may be achieved thereby reducing the number of valve parts and potential leak paths. When a valve is in a fully open position, the mechanical stop may make contact with a valve piston. The mechanical stop may therefore act as a "bump stop" with a valve piston. This may occur when piston lift reaches the point where over-compression of the spring may start to occur.

The receiving member which may sometimes be referred to as an adjusting gland, or similar, may be adjusted in order to set the valve. When the valve is being set, the adjusting gland may be used to tighten and compress the spring. The spring may therefore be compressed by a required amount corresponding to the pressure set value of the valve. A further advantage is the provision of a one piece valve body design.

The mechanical stop may either be a separate unit from the receiving member acting as an adjusting gland, or alternatively, the mechanical stop and adjusting gland may be an integral single unit.

The present invention provides a number of technical advantages, such as preventing over-compression of a spring. In an advantageous embodiment, the mechanical stop may be received inside a spring providing the advantageous feature of keeping the spring straight and preventing any buckling action occurring. This is particularly important when the valve opens (i.e. pops).

A further advantage of the present invention is that it reduces the range of springs required. Because spring compression can now be specifically designed for different modes of operation and optimised as required, a designer may use a higher maximum set pressure for any given spring design. This means that a single spring design as set out in the present invention may be used over a greater pressure range. For example, for a valve design that may be set between 14 to 31 barg, three different spring designs would normally be required to cover this pressure range. Typically, using the spring valve as set out in the present invention, a single spring design may now be used to cover the same range. Therefore, reducing the number of spring designs has significant assembly benefits for a valve manufacturer. It also has economic benefits, allowing a valve company to purchase fewer spring designs, but at higher quantities, thus enabling cost savings.

A further advantageous feature of the present invention, is that maximum piston lift may be controlled. In safety valve design, piston lift is a difficult parameter to control. By using a mechanical stop according to the present invention, a designer may control the maximum possible piston lift. Controlling piston lift is an important feature of safety valve design. Piston lift affects flow capacity through a valve and may affect the re-seating pressure of a valve. A further advantage is the provision of a one piece valve body design.

According to a second aspect of the present invention, there is provided a method of controlling the compression of a valve spring arrangement by providing a mechanical stop which is adapted to engage with a piston, thereby preventing over-compression of a spring.

Typically, the mechanical stop may be adapted to interact and engage with any part of the piston such as a front face of a piston or any other intermediary part of a piston arrangement such as a washer or linking element.

According to a third aspect of the present invention there is provided a safety valve spring arrangement comprising a mechanical stop, said mechanical stop capable of controlling and/or limiting the compression of a valve spring.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a side sectional view of a safety valve according to an embodiment of the present invention in a closed position;

Figure 2 is a side sectional view of the safety valve arrangement shown in Figure 1 in an open position; Figure 3 is a side sectional view of a safety valve with a washer according to a further embodiment of the present invention in a closed position;

Figure 4 is a side sectional view of the safety valve arrangement shown in Figure 3 in an open position; and

Figure 5 is a side sectional view of a further embodiment of the present invention with a hollow piston and spring stop.

DETAILED DESCRIPTION

Referring to Figure 1, there is a schematic representation of a side sectional view of a safety valve, generally designated 10. The safety valve 10 comprises an outer housing 12 defining an inner chamber

14.

The inner chamber 14 contains a mechanical stop 16 which is received within an aperture in an adjusting gland 18. Around the mechanical stop 16, there is a spring 20. The spring 20 is helical in conformation but may have other suitable forms. Towards the bottom of the valve 10, there is a piston 22 and a valve seat 24.

As shown in Figure 1, which is the valve 10 in a closed position, the mechanical stop 16 is in a substantially cylindrical form. The mechanical stop 16 is securely engaged within a recess in the adjusting gland 18.

In the closed position as shown in Figure 1, the piston 22 does not make contact with the mechanical stop 16. The distance, Li, between the piston 22 and the mechanical stop 16 allows for piston lift when a valve opens .

The mechanical stop 16 may be of any suitable shape and may be manufactured from any suitable material such as any suitable plasties, polymeric material or metal/alloy.

In an alternative embodiment to that shown in Figure 1, the mechanical stop 16 and adjusting gland 18 may be an integral unit .

Figure 2 represents the valve 10 in an open position. As clearly shown in Figure 2, the piston 22 abuts against the mechanical stop 16. The distance, L₂, is the amount of piston lift that the mechanical stop 16 allows (i.e. L₂ = L_x). The mechanical stop 16 therefore prevents any further upward movement of the piston 22 or spring 20.

In the valve open position, the resulting spring length, L₃, corresponds to the maximum allowable compressed length of the spring 20.

In alternative embodiments, the length of the mechanical stop 16 may be adjustable to allow for different settings. Additionally, the position of the adjusting gland 18 may be adjusted within the inner chamber 14 of the valve 10, thereby, once again, allowing the operational parameters of the valve spring 10 to be optimised and adjusted for different required conditions.

Figures 3 and 4 represent a further embodiment of the present invention. Corresponding reference numerals to that used in Figures 1 and 2 for the same features are used with the prefix "1". Figures 3 and 4 therefore relate to a valve generally designated 100 which has an outer housing 112 defining an inner chamber 114.

The inner chamber 114 contains a mechanical stop 116 which is received within an aperture in an adjusting gland 118. Around the mechanical stop 116, there is a spring 120. At the bottom of the valve 100, there is a piston 122 and a valve seat 124. Figure 3 represents the valve 100 in a closed position, and Figure 4 represents the valve in an open position. Figure 3 shows the mechanical stop 116 securely engaged within a recess in the adjusting gland 118. Figure 3 which shows the valve 100 in a closed position, shows that the piston 122 does not make contact with the mechanical stop 116. The distance Li, between the piston 122 and the mechanical stop 116 allows for piston lift when a valve opens. Figure 4 represents the valve 100 in an open position. Figure 4 shows that the piston 122 abuts against the mechanical stop 116. The distance L₂ is the amount of piston lift that the mechanical stop 116 allows

(i.e. L₂ = Li). The mechanical stop 116 therefore prevents any further upward movement of the piston 122 or spring 120.

In the valve open position, the resulting spring length, L₃, corresponds to the maximum allowable compressed length of the spring 120. The main difference in the valve 100 shown in Figures 3 and 4 is that a spacer 125 has been placed between the spring 120 and a circumferential edge 130 on the spring stop 116. The spacer 125 has the purpose to align the spring stop 116 in a substantially vertical position so that when it makes contact with the piston 122, the force is more uniform/centralised. If the spring stop 116 sits on the spring 120 directly, some misalignment may occur from manufacturing inconsistencies of the spring end coil. Figures 3 and 4 also show that the piston 122 has a protruding centralised member 123 which helps to locate and stabilise the spring 120.

Figure 5 represents a further safety valve 200 according to the present invention. Similar to the previous embodiments, the safety valve 200 comprises an outer housing 212 defining an inner chamber 214. There is a spring 220, a valve seat 224 and a protruding member 223 at the lower end of the valve 200 used for locating the spring 220. The main difference in the safety valve 200 is that the piston 222 and the spring stop 216 comprise a central passageway (i.e. are hollow) to allow liquid/gas flow through. This is advantageous in certain valve designs.

Whilst specific embodiments of the invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the invention. For example, any suitable shape of mechanical stop may be used to control the compression of a spring. Additionally, the mechanical stop may be located at any position within a chamber of a valve. The mechanical stop may also be adjustable in length and may be made from any suitable material. The mechanical stop may be made from one or more parts . The mechanical stop may also be manufactured as a single separate unit or may be integrally formed with an adjusting gland.

Claims

1. A valve spring arrangement comprising a mechanical stop, said mechanical stop capable of controlling and/or limiting the compression of a valve spring.

2. A valve spring arrangement according to claim 1, wherein the mechanical stop functions as a spring stop and is adapted to control and/or limit the compression of the valve spring.

3. A valve spring arrangement according to any of claims 1 or 2, wherein the valve spring allows sufficient movement to counter forces during pressure setting.

4. A valve spring arrangement according to any preceding claim, wherein the valve spring allows additional travel to allow a valve piston or plunger to move away from a seat when a valve opens .

5. A valve spring arrangement according to any preceding claim, wherein the valve spring comprises a plurality of valve springs in series.

6. A valve spring arrangement according to any preceding claim, wherein the valve spring arrangement is adapted to allow a piston to move away from a seat by a suitable distance, to allow flow through the valve spring.

7. A valve spring arrangement according to any preceding claim, wherein the maximum spring travel allowed is about 10 - 90% which prevents over-compression of the valve spring.

8. A valve spring arrangement according to any preceding claim, wherein the mechanical stop is adapted to be received within the valve spring.

9. A valve spring arrangement according to any preceding claim, wherein the mechanical stop is a tubular-like form or any other suitable form, adapted to be received within an inside perimeter of the valve spring.

10. A valve spring arrangement according to any preceding claim, wherein the length of the mechanical stop is adaptable to form different required lengths.

12. A valve spring arrangement according to any preceding claim, wherein the mechanical stop is made from any plastics, polymeric, composite or metal/alloy material.

13. A valve spring arrangement according to any preceding claim, wherein at an end opposite to that of a valve seat, the mechanical stop is adapted to be received within a receiving member.

14. A valve spring arrangement according to claim 13, wherein the receiving member is an adjusting gland.

15. A valve spring arrangement according to any of claims 13 or 14, wherein the receiving member is movable up and down within a chamber of a valve to provide different valve arrangements and pressure settings.

16. A valve spring arrangement according to any of claims 13 to 15, wherein an end of the mechanical stop intended to be received in the receiving member is substantially conical in shape or any other suitable form.

17. A valve spring arrangement according to any preceding claim, wherein when the valve is in an open position, the mechanical stop contacts a valve piston, either directly or indirectly.

18. A valve spring arrangement according to any of claims 13 to 17, wherein the receiving member is adjustable in order to set the valve.

19. A valve spring arrangement according to any preceding claim, wherein the mechanical stop and a receiving member are an integral single unit.

20. A valve spring arrangement according to any preceding claim, wherein the mechanical stop is capable of keeping the spring straight and preventing any buckling action occurring.

21. A valve spring arrangement according to any preceding claim, wherein the valve spring arrangement allows piston lift to be controlled by using the mechanical stop.

22. A valve spring arrangement according to any preceding claim, wherein a spacer is located on a circumferential edge of the valve spring which facilitates the alignment of the mechanical stop.

23. A valve spring arrangement according to any preceding claim, wherein a piston in the valve spring arrangement and the mechanical stop comprise a passageway allowing liquid/gas to flow therethrough.

24. A method of controlling the compression of a valve spring arrangement by providing a mechanical stop which is adapted to engage with a piston, thereby preventing over-compression of a spring.

25. A method of controlling the compression of a valve spring arrangement according to claim 24, wherein the mechanical stop is adapted to interact and/or engage with a part of the piston.

26. A method of controlling the compression of a valve spring arrangement according to claim 25, wherein the part of the piston is a front face of the piston or an intermediary part of a piston arrangement.

27. A method of controlling the compression of a valve spring arrangement according to claim 26, wherein the intermediary part of the piston arrangement is a washer or linking element.