Pressure relief valve

Field of the invention

The present invention relates to a pressure relief valve for pressure equalization between a closed space and the surrounding atmosphere. More specifically the invention relates to the field of high-speed pressure relief valves.

Such pressure relief valves are especially used as pressure relief means in settings where e.g. a cargo or a stationary stock of goods emits gasses at a variable rate. Such setting may comprise tanks for combustible carbohydrates, especially during filling of such tanks, chemical cargos, asphalt or solid cargos such as fruit, which will eventually emit gasses when stored.

Valves of this kind are usually combined with vacuum valves in pressure-vacuum high-speed valves. The performance of such valves is subject to demand and international regulations reflected in e.g. IMO MSC/Circ 677 from the International Maritime Organization and the European Standard EN 12874.

Background of the invention

A common problem for pressure relief valves used in settings where gas is emitted from a substance confined in a closed space in a constant or variable rate is a phenomenon called hammering or oscillation.

Pressure relief valves are designed to open at a certain pressure that may be built up within the closed space, and to close when the pressure returns to a certain lower pressure. In such systems there is often a tendency for the valve to open and close very quickly - a phenomenon known as hammering. Hammering/ oscillation occurs due to an imbalance caused by a pressure loss in the valve and the pipe system downstream the valve such that the valve under certain operating conditions moves between its extreme positions (open/closed) at a rate of considerably above 0.5 Hz. This movement causes hard impacts between the valve member and the valve seat (in closed position) and between the valve member and the valve stop (in open position), which over time will wear the

involved parts. Thus, hammering is highly undesirable, because parts of the valves will experience an increased wear and tear, causing a need for continuous maintenance and/or replacement of valves or valve parts. Hammering also causes the gas exhaust rate from the valve between the valve seat and the valve member to decrease, whereby a desired flame impeding property of such valves is reduced or eliminated.

Further, the above mentioned regulations require the hammering phenomenon to be eliminated or reduced, in order to preserve the above mentioned flame impeding characteristics of the valves.

Pressure relief valves are known in the art. An example of such a valve is shown in WO 02/095275 Al. This valve has magnetic means for securing a certain opening pressure of the valve and a lifting plate for aiding the lift of the valve member. Since the area of the lifting plate must be larger than the exhaust opening defined at the valve seat in order secure flow dynamics, this valve has a complicated geometric structure of the valve housing. Due to the flow dynamics around the lifting plate hammering is only limited, but not entirely reduced. Further the design of this valve is complex, leading to high production and maintenance costs and impedes easy maintenance.

Further, the geometry of this type of valves gives problems with regard to the clearance between the lifting plate and the valve housing wall. There is a limited clearance between the lifting plate and the valve housing wall, making this kind of valves unsuitable especially for sticky, crystallizing and freezing cargo types. In the prior art, this is partly compensated for by the bell shape of the valve housing, which in return causes flow dynamics problems.

Hence, an improved pressure relief valve would be advantageous, and in particular a more simple, a more efficient and/or reliable pressure relief valve would be advantageous.

Object of the invention

It is an object of the invention to provide a pressure relief valve for pressure equalization between a closed space and the surrounding atmosphere eliminating hammering/oscillation characteristics.

It is a further object of the present invention to provide a pressure relief valve having increased life span, and reduced maintenance time and costs.

It is a further object of the present invention to provide a pressure relief valve having a simplified construction, which is easy and cost efficient to manufacture, maintain and repair.

It is a further object of the present invention to provide an alternative to the prior art pressure relief valves for pressure equalization between a closed space and the surrounding atmosphere.

In particular, it may be seen as an object of the present invention to provide a pressure relief valve that solves the above mentioned problems of the prior art.

Summary of the invention

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a pressure relief valve comprising

• an elongate valve housing having o an inlet end connectable to a closed space, o an outlet end disposed opposite to said inlet end in said housing, o a longitudinal central axis, and o a substantially uniform first inner width perpendicular to said central axis taken in a cross section along said central axis from said inlet end to said outlet end,

• a valve seat arranged at said outlet end and having a second inner width perpendicular to said central axis taken in a cross section along said central axis,

• a valve member arranged to cooperate with said valve seat, and being arranged for translational movement in a direction along said axis to provide opening and closing of said valve,

• means for providing a resistance to opening of said valve

• a lifting member arranged between said inlet end and said outlet end, and having a third outer width perpendicular to said central axis taken in a cross section along said central axis, and a height defined between a first end facing said inlet end and a second end facing said outlet end; and

• a connection between said valve member and said lifting member whereby the lifting member and the member are arranged for simultaneous translational movement along axis wherein the height of the lifting member is equal to or larger than the third width of the lifting member.

The objects of the invention are further obtained from the embodiments described in the dependent claims 2-11.

Brief description of the drawings

The pressure relief valve according to the invention will now be described in more detail with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

• Fig. 1, in a partly sectional view, shows a pressure-vacuum high speed valve with a pressure relief valve according to an embodiment of the invention.

• Fig. 2, in a sectional view, shows details of a pressure relief valve according to an embodiment of the invention.

• Fig. 3 shows a system comprising a closed space in the form of a tank and showing various arrangement of a pressure relief valve; and

• Fig. 4 shows behavioural characteristics of a pressure relief valve according to an embodiment of the invention in a test study.

Embodiments of the invention

In figure 1 a pressure-vacuum high speed valve 100 is shown. The right-hand side of the figure shows a pressure relief valve 1 according to an embodiment of the invention. The left hand side of the drawing involves a vacuum-part of this valve 100, and does not constitute a part of the invention.

It should be emphasised that the pressure relief valve 1 according to the invention may be used in combination with such a vacuum-valve or may constitute a separate entity.

The pressure relief valve 1 comprises a housing 10, having a valve seat 20, a valve member 30 arranged for translational movement along a central longitudinal axis A of the valve housing 10 between a closed position in which the valve member 30 abuts the valve seat 20 and an open position in which the valve member 30 is moved away from the valve seat 20 to provide an exhaust opening for a gas flowing through the valve housing 10. The valve housing 10 has a first inlet end 11 that is adapted for mounting on a closed space Ia, such as a tank, or on tubing Ib being in communication with such a closed space Ia as shown in Fig. 3. The valve housing 10 further has an outlet end 12 arranged diametrically opposed to the inlet end 11 along the axis A on the housing 10. The valve seat 20 is arranged at the outlet end 12.

The pressure relief valve 1 is intended to be mounted with the outlet end 12 facing up and the inlet end 11 facing down with respect to gravity, such that the central longitudinal axis, A, is upright or vertically oriented.

The valve housing 10 has a substantially uniform inner width wl taken in a direction perpendicular to the elongate axis from the inlet end 11 to the outlet end

12 as seen in any section through the valve housing 10 along the central axis A. Preferably, the housing 10 forms a cylindrical inner space 16, such that wl is a diameter of a circular cross-section of the space 16 taken perpendicularly to said central longitudinal axis A. However, the inner space 16 may, in other 5 embodiments (not shown) have another cross sectional shape e.g. octagonal or other polygonal shapes.

By substantially uniform width is meant that the width may vary e.g. due to production tolerances and also that there may be provided tubing in- or outlets, 10 windows 17, etc. in the inner wall defining inner space 16.

The valve seat 20 forming the outlet from the valve 1 has a width w2 taken in a section including said central longitudinal axis A and in a direction perpendicular thereto. The valve seat 20 is preferably circular; the width w2 being a diameter. 15 The width w2 of the valve seat 20 is preferably the same or only slightly smaller than the width wl of the inner space 16 of the housing 10.

A valve member 30 is arranged to cooperate with the valve seat 20 in the closed position of the valve. The valve member 30 is situated exterior to the inner space

20 16, and is arranged for translational movement along the central axis A, between a closed position (se Figs. 1 and 2) with a part of the lower side of the valve member 30 cooperating with valve seat 20, and an open position (not shown) in which the valve member 30 is moved away from the valve seat 20 to form an exhaust opening through which a gas may escape between the valve seat

25 20/outlet end 12 of the housing 10 and the lower side of the valve member 30.

The valve member may be mounted on a shaft 61 formed along axis A of the housing, said shaft 60 being slidably arranged with respect to holding means 18, 19 formed in relation to the valve seat 20 and /or the housing 10. A stop 65 is 30 formed on said shaft 60 in an end opposite to the valve member 30, to limit the opening of the valve 1, e.g. by abutment of said stop on holding member 19, or by other suitable means provided in said housing 10.

A lifting member 50 is provided on said shaft 61, the lifting member being 35 arranged in the inner space 16 of the housing 10. The shaft 61 thus forms a

connection 60 between the valve member 30 and the lifting member 50. This connection is fixed, such that the lifting member, the connection 60 (in this embodiment the shaft 61) and the valve member 30 are slideably arranged as a single entity or aggregate, although they may for manufacturing purposes be formed as individual parts being joined together during manufacture.

Other ways of providing and guiding the translational movement of the valve member 30 may be arranged, e.g. by guides outside the inner space 16. Also, the connection 60 between the lifting member 50 and the valve member 30 may be separate from each other (not shown).

The lifting member 50 is arranged between said inlet end 11 and said outlet end 12. It has a third outer width w3 perpendicular to said central axis A taken in a cross section along said central axis A, and a height h defined between a first end 51 facing said inlet end 11 and a second end 52 facing said outlet end 12.

Means 40, for providing a resistance to opening of said valve are provided between the housing 10 and the aggregate comprising the valve member 30, the connection 60 and the lifting member 50. Such means 40 may be provided in the valve member 30, in the form of a magnet or a magnetisable body arranged for cooperating with a magnet or a magnetisable body formed in connected to the housing 10. The pair 40 of magnets/magnetisable bodies forms means 40 for providing a downwardly (in relation to the intended use) oriented abutment force, Fc that contains contributions from the mass of the valve member 30, the mass of the connection 60, the mass of the magnet/magnetisable body (depending on which of these parts is mounted on the connection 60 or valve member 30), and from the force of attraction Fm between the magnet and the magnetisable body. The abutment force Fc is thus to be understood as the force that keeps the pressure valve closed, i.e. the closing force of the pressure valve.

The magnetisable body is configured for being able to cooperate with the magnet in the closed state of the pressure valve 1. The magnet and the magnetisable body being located in the area at the outlet end 11, is preferred when there is a need for achieving regular access to the magnet, e.g. in the event of maintenance.

However, the magnet and magnetisable body may alternatively be mounted in association with the connection 60 at the end being located within the inner space 16 and away from/opposite to the valve member 30, and below the lifting member 50. It may be either a permanent magnet or e.g. an electro-magnet.

When, in the closed space, the pressure rises above atmospheric pressure, such pressure will, due to the gap between lifting member an the inner wall of housing 10, also reign in the space between the lifting member 50 and the valve member 30. The pressure in this space is thereby equal to the pressure within the closed space (tank), and the pressure influences the top face and lower face of the lifting member 50 by the same force. As long as the superatmospheric pressure does not give rise to an upwardly oriented force on the valve member 30 that exceeds the closing force Fc of the pressure valve, the pressure valve will remain in the closed state. The upwardly oriented force on the valve member 30 can be determined as the superatmospheric pressure in the container multiplied by the area of the opening defined by the valve seat 20.

When the superatmospheric pressure exceeds the closing force Fc of the pressure relief valve, the pressure relief valve opens. The outflow of gas causes the pressure on the face of the lifting member 50 that faces towards the outlet end 12 to drop. The upwardly oriented movement of the valve member 30 towards the entirely open position of the pressure relief valve 1 is then controlled to a certain extent by the force exerted by the flowing gas on the lower face 51 of the lifting member 50 and the gas passing over the outer side wall 54 of the lifting member. This first influence can be determined as the superatmospheric pressure of the container multiplied by the area defined by the cross sectional area of the lifting member 50. The lifting power of the gas on the lifting member 50 increases, and the rate of movement of the lifting member 50 and hence of the valve member 30 (because they are interconnected vi connection 60, i.e. shaft 61) in a direction towards the entirely open state of the pressure valve increases, thus aiding in keeping the valve member 30 "floating".

The valve member 30 is kept in the open position by the flowing gas. The downwardly oriented force on the valve member 30 contains contributions from the mass of the valve member 30, the mass of the connection 60, the mass of

either the magnet or the magnetisable body, depending on which of the two parts is mounted on the connection 60/valve member 30. The force of attraction Fm between the magnet and the magnetisable body does not significantly contribute as soon as the valve member 30 has moved slightly away from the position shown in Figs. 1 and 2.

Experiments has shown that if the height, h, of the lifting member 50 is equal to or larger than the third width w3 of the lifting member 50 the lifting member will cause the valve member 30 to "float" in the gas flow, thus avoiding the phenomenon of hammering/oscillation.

The third width w3 of the lifting member 50 is preferably smaller than the second width w2 of the valve seat 20 opening such that the cross sectional area of the lifting member is smaller than the cross sectional area of the valve seat 20 aperture. Thus the lifting member is easily mounted inside the housing 10 during manufacture and also in event of maintenance and/or repair.

The third width w3 of the lifting member 50 is preferably between 60 and 90% of the first inner width wl of the valve housing 10, whereby a sufficient space between the lifting member and the inner wall of the housing 10 is provided

In a preferred embodiment the third width w3 of the lifting member 50 is 80% of the first inner width wl of the valve housing 10.

As can be appreciated from the figures, the lifting member 50 preferably has a uniform outer width w3 from said first end 51 facing said inlet end 11 and said second end 52 facing said outlet end 12.

The valve member 30 is preferably shaped such as to collect a gas flow through the valve 1, when exiting past said valve seat 20. This may obtained by forming the valve member in a drop shape or conical shape (Figs. 1 and 2). Thus a vertical flow of the exhausted gas may be obtained.

In an embodiment the pressure relief valve 1 the of the first inner width wl of the valve housing 10 is 100mm, the third width w3 of the lifting member 50 is 80mm diameter and the second width w2 of the valve seat 20 opening is 90mm

As shown in the figures the lifting member 50 may be hollow. In figs. 1 and 2 this is provided by a cavity in the bottom of the lifting member, but may as well be provided by an upwardly facing cavity or a closed cavity of the lifting member 50. By a hollowed lifting member it is obtained that the mass of the lifting member may be adjusted to provide an optimal operation of the valve 1. The above mentioned regulations set limits on the materials that may be used for the parts of such a valve. The hollow lifting member thus allows a certain height h of the lifting member to be gained without necessarily having too high mass.

The lifting member may be formed in stainless steel.

The distance d between the contact surface 31 of the valve member 30 to the valve seat 20 to the upper, second end 52 of said lifting member 50 is arranged such that the second end 52 of said lifting member 50 in open state of the valve 1 is at least 15 mm, such as between 25-30 mm.

In one embodiment the inner diameter of the housing 10 is 100 mm, the diameter of the lifting member 50 is 80 mm and the valve seat opening is 90mm. The mass of the aggregate of the lifting member the valve member may be 4.3 kg, 4.6 kg or 4.7kg.

The later embodiment has been tested, and proved to eliminate the hammering phenomenon. Test result is illustrated in Fig. 4.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements

indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.