SHUT-OFF VALVE FOR LIQUIFIED NATURAL GAS

Technical field

[0001] The invention is directed to a valve for pressurized gas, more particularly for pressurized gas operating at low temperature like liquefied natural gas (LNG).

Background art

[0002] Prior art patent document published CN 202140576 U discloses a low- temperature shut-off valve comprising a body with a gas inlet, a gas outlet and gas passage between the inlet and outlet, a hand wheel and shut-off device in the valve body for closing the gas passage by operating the hand wheel. The shut-off device comprises a movable closure member that is in threaded engagement with the body. A spindle supporting the hand wheel rotatably engages with the movable closure member. The spindle comprises a shoulder abutting against a corresponding shoulder on a cap portion of the body. A first gasket is provided between the shoulder of the spindle and the corresponding shoulder of the cap portion. This first gasket is ring shaped with a L-shaped cross-section. A portion of the gasket extends between the external surface of the spindle and the internal surface of the body. A second gasket is arranged around the spindle at a location that is more distal from the shut-off device. This second gasket is housed in the cap portion and is pressed by a sleeve that is in contact with the hand wheel via a sliding washer. The hand wheel is able to slide along the spindle and a spring is arranged between a distal end of the spindle and the hand wheel so as to press it towards the valve body. This urging force is transmitted to the sleeve via the sliding washer. This force is then further transmitted to the second gasket for pressing it against the external surface of the spindle.

[0003] During operation of the above valve at low temperature, e.g. at less than -100°C and even less than -150°C, as is usual with LNG, the gaskets made of elastomer become hard and frictional movement against them can produce elastomer particles. These particles can accumulate inside the valve and increase the torque necessary for operating it. Such valves require already a relatively high torque for operating them due essentially to the low temperatures and the resulting high stiffness of the gaskets. Any sensible increase in the operating torque is to be avoided.

Summary of invention

Technical Problem

[0004] The invention has for technical problem to provide a valve that overcome at least one of the drawbacks of the above mentioned prior art. More particularly, the invention has for technical problem to provide a valve that is suitable for gases at low temperatures, e.g. below -100°C, while keeping a reduced operating torque and being gas tight.

Technical solution

[0005] The invention is directed to a valve for gas under pressure, in particular at temperatures below -100°C, comprising: a body with a gas inlet, a gas outlet and a passage connecting said inlet with said outlet; a shut-off device for closing the gas passage; a spindle designed for operating the shut-off device; at least one gasket between the spindle and the body; wherein the valve further comprises at least one cavity around the spindle for accumulating particles separated from the at least one gasket while operating the spindle and the shut-off device, in particular at temperatures below -100°C.

[0006] According to a preferred embodiment, the valve comprises a first gasket and a second gasket, and a first cavity at least one cavity being between said first and second gaskets.

[0007] According to a preferred embodiment, the first cavity is shaped as a groove on the external surface of the spindle.

[0008] According to a preferred embodiment, the cross-section of the first cavity is generally rectangular shaped with a width that is more than 5 times higher, preferably 10 times higher, than the height. The width is meant to be measured parallel to the longitudinal axis of the spindle and the height is meant to be measures perpendicularly to the axial direction. [0009] According to a preferred embodiment, the cross-section of the first cavity is generally rectangular shaped with a width that is comprised between 1 mm and 8mm, preferably between 1 mm and 5mm, and/or a height that is comprised between 0.1 mm and 1 mm, preferably between 0.1 mm and 0.5mm.

[0010] According to a preferred embodiment, the first cavity is in front of a cylindrical internal surface of the body that supports the spindle.

[001 1] According to a preferred embodiment, the spindle comprises a shoulder axially abutting against a corresponding shoulder of the valve body, the first gasket being positioned between said shoulder of the spindle and said shoulder of the body.

[0012] The first gasket preferably has an at least generally rectangular cross- section.

[0013] According to a preferred embodiment, the shut-off device comprises a movable closure member housed in the valve body, said member cooperating with a seat around the gas passage in the body, a second cavity of the valve being formed in said member, the spindle engaging with said second cavity for actuating said member.

[0014] According to a preferred embodiment, the second cavity widens towards the spindle so as to be able to collect the particles separated from the first gasket while operating the spindle and the shut-off device.

[0015] According to a preferred embodiment, the second cavity widens up to the maximum diameter of the shoulder of the spindle.

[0016] According to a preferred embodiment, the external surface of the shoulder of the spindle tapers towards the closure member, the internal surface of second cavity on said member being shaped to conform to the tapering external surface of said shoulder.

[0017] According to a preferred embodiment, the movable closure member is in threaded engagement with the body, and the engagement between the spindle and the second cavity is in rotation. The spindle and the second cavity can slide relative to each other. [0018] According to a preferred embodiment, the second cavity extends opposite to the spindle, beyond a proximal end of said spindle in said cavity to create a space for accumulating the particles from the at least one gasket.

[0019] According to a preferred embodiment, the body comprises a main portion that houses and guides the movable closure member, and an auxiliary cap portion that is screwed on said main portion and that bears the spindle, the first gasket and/or the second gasket.

[0020] According to a preferred embodiment, the auxiliary cap portion comprises a bore portion surrounding the shoulder of the spindle and configured for receiving, when the shut-off device is in an open position, an end of the movable closure element corresponding to the opening of the second cavity.

[0021] According to a preferred embodiment, the shoulder of the spindle comprises a surface that extends radially and that contacts the first gasket, said surface being raised at its external portion, and/or the shoulder of the valve body comprises a surface that extends radially and that contacts the first gasket, said surface comprises at least one rib at its external portion that penetrates said gasket.

[0022] According to a preferred embodiment, the second gasket cooperates with the cylindrically shaped external surface of the spindle, at an axial position of the spindle that is more distant from the shut-off device than the first gasket.

[0023] According to a preferred embodiment, it further comprises: a hand wheel in rotational engagement with the spindle; a sleeve around the spindle between the hand wheel and the second gasket; and resilient biasing means acting between a distal end of the spindle and the hand wheel so as to axially press the hand wheel against the sleeve and thereby press the second gasket.

[0024] According to a preferred embodiment, the second gasket is a ring with a generally trapezoid cross-section with the larger base in contact with the spindle and the smaller base in contact with the body.

[0025] According to a preferred embodiment, one leg of the trapezoid cross- section of the second gasket is against a corresponding bevelled surface of the body and the other opposite leg of the trapezoid is against a corresponding bevelled surface of the sleeve.

[0026] According to a preferred embodiment, the larger base of the trapezoid cross-section of the second gasket comprises a recess, preferably at a middle portion.

[0027] According to a preferred embodiment, the resilient biasing means comprises stacked Belleville washers.

[0028] According to a preferred embodiment, it comprises a cage housing the resilient biasing means and limiting the compression of said means by the hand wheel.

Advantages of the invention

[0029] The invention is particularly interesting in that its features permit to limit the torque necessary for opening and closing the valve, in particular when used with gases at low temperatures where the gaskets, usually made of elastomer materials, become hard and stiff. This is particularly true for valves which cannot contain any loose lubricant like lubricating oil or grease.

Brief description of the drawings

[0030] Figure 1 is a sectional view of a valve in accordance with the invention.

[0031] Figure 2 is a magnified view of the area II in figure 1.

Description of an embodiment

[0032] The valve 2 illustrated in figure 1 comprises essentially a body 4, a gas inlet 6, a gas outlet 8 and a gas passage 10 fluidly interconnecting said inlet 6 and outlet 8.

[0033] A shut-off device consisting essentially of a movable closure member 12 is provided in the body 4 for closing the gas passage 10. The movable closure member 12 is operated by a spindle 14 extending through the valve body 4.

[0034] The valve body 4 is comprised of a main portion 16 and a cap 18 that is attached to the main portion 16, preferably by screwing. The main portion comprises a bore that houses the movable closure member 12, the spindle 14 and the cap 18. The movable closure member 12 is generally cylindrically shaped and comprises at its external surface a male thread that engages a corresponding female thread on an internal surface of the bore of the main portion 16 of the body. It comprises a front surface with a recess housing an element 12 ¹ of softer material that cooperates in a tightly fashion with a valve seat 20 that is formed in the valve body 4 around the gas passage 10. The element 12 ¹ can be made of plastic material.

[0035] The movable closure member 12 comprises also a cavity 12 ² that opens in a direction that is opposite to the element 12 ¹ and the valve seat 20. This cavity 12 ² comprises a cylindrical internal surface that receives and engages in rotation only with a proximal end 14 ¹ of the spindle 14. The proximal end 14 ² of the spindle 14 and the internal surface of the cavity

12 ² of the closure member 12 can take various shapes which are as such well known from the skilled person, e.g. splines or any section that is not symmetrical in rotation.

[0036] The spindle 14 comprises a shoulder 14 ² that cooperates with a corresponding shoulder 18 ¹ and bore 18 ² on the cap 18. A generally ring shaped first gasket 22 is housed in the chamber delimited by these two shoulders 14 ² and 18 ¹ and the bore 18 ² .

[0037] The external surface 14 ³ of the shoulder 14 ² of the spindle 14 can be bevelled so as to taper towards the shut-off device 12. The shoulder 14 ² of the spindle 14 at the maximum diameter of the tapering external surface 14 ³ closes the chamber that houses the first gasket 22 while keeping a minimal surface of contact between the external surface 14 ³ of the spindle and the corresponding surface of the bore 18 ² of the cap 18.

[0038] In addition, the cap 18 forms a second bore 18 ³ , larger than the first one bore 18 ² and positioned in front of the tapering external surface 14 ³ of the shoulder 14 ² of the spindle 14. This bore 18 ³ can receive the raised end

12 ³ of the movable closure member 12 that is opposed to the valve seat 20.

[0039] The cavity 12 ² in the movable closure member 12 widens towards the spindle 14, thereby forming the raised end 12 ³ . When operating the spindle 14, the frictional forces acting on the first gasket 22 are likely to produce particles of the elastomer material of said gasket. Under the condition that the valve is positioned upwardly as illustrated in figure 1 , i.e. with the axis of the spindle generally vertical and with the distal end 14 ⁴ of the spindle 14 oriented upwardly, the particles separating from the first gasket 22 can fall downwardly by gravity and be collected by the funnel- shaped upper internal surface of the cavity 12 ² . The particles can then pass through the mechanical play between the external surface of the proximal end 14 ¹ of the spindle 14 and the corresponding internal surface of the movable closure member 12, and then accumulate at the bottom of the cavity 12 ² .

[0040] As is visible in figure 1 , a passage 12 ⁴ can be foreseen at the bottom of the cavity 12 ² , interconnecting said cavity with the housing for the element 12 ¹ cooperating with the valve seat 20.

[0041] The valve 2 comprises a second gasket 24 that is ring-shaped and with a trapezoid cross-section. The larger base of the trapezoid cross-section is in contact with the external cylindrical surface of the spindle 14 whereas the smaller base is in contact with the internal surface of the cap 18. A sleeve 26 is slidably provided around the spindle 14 for pressing the second gasket 24.

[0042] The spindle 14 comprises at its external surface a groove 28, said groove being between the first gasket 22 and the second gasket 24. The groove forms a cavity that can accumulate particles separated from the gaskets 22 and 24, more particularly from the second gasket 24, similarly to the cavity 12 ² in the movable closure member 12. The groove 28 can have a generally rectangular cross shape with a width that is larger, preferably at least 5 times larger, and more preferably at least 10 times larger than the height.

[0043] The valve 2 comprises a hand wheel 30 that is in rotatable engagement with the distal end 14 ⁴ of the spindle 14. The hand wheel 30 can slide along the spindle while being in rotatable engagement. To that end the spindle 14 can provide a cross-section with a non-circular outer surface, e.g. a square outer surface, that engages with a corresponding inner surface of the hand wheel 30. A sliding or anti-friction washer 32 can be interposed between the lower surface of the hand wheel 30 and the upper surface of the sleeve 26. A stack of Belleville spring washers 38 is provided around the distal end 14 ⁴ of the spindle 14, between a nut 34 that is engaged with said distal end, and the hand wheel 30. The spring washers 38 can be housed in an opened housing 36 that is interposed between the nut 34 and the springs 38 and that extends at the lateral surface of the springs up to close to the surface of the hand wheel that is in contact with the spring washers. The spring washers exert a biasing force on the hand wheel that is oriented downward, i.e. in the direction of the valve body so as to transmit that force to the sleeve 26 and to the second gasket 24. The second gasket 24 is thereby constantly under pressure so as to cooperate in a gas tight fashion with the spindle 14. The biasing force of the springs is also transmitted to the spindle 14 by means of the nut 34. The spindle 14 is then biased upwardly, i.e. in a direction opposite to the valve body and that presses the first gasket 22 between the shoulders 14 ² and 18 ¹ , so as to provide a first gas tight barrier between the spindle 14 and the body 4.

[0044] The use of the housing 36 for the resilient biasing means 38 is interesting for it permits to keep the washers in position so as to work properly. It permits also to facilitate the assembly of the valve. Indeed, when tightening the nut 34 in order to pre-stress both first and second gaskets 22 and 24, the nut can be tighten until the housing 36 contacts the hand wheel 30, so as to ensure a minimum and also an adequate pre-stress of the gaskets. Any wear or matting of one or both of the gaskets will be compensated by the biasing force of the pre-stressed resilient means 38.

[0045] During operation of the valve, in particular at low and very low temperatures, i.e. less than -100°C, or even less than -150°C, which is typical for liquefied natural gas (LNG), the material of the gaskets 22 and 24 becomes hard and stiff. The contact pressure between the gaskets and the spindle resulting from the mechanical pre-stress and/or the fluid pressure has for effect that the material of the gaskets can be subject to mechanical wear during rotation of the spindle, the wear resulting in the separation of material in small particles or even powder. These particles can accumulate at some places in the valve, in particular between moving parts and non-moving parts, leading to an increase of the operating torque or even a blocking of the valve. The cavity 28 formed on the outer surface of the spindle 14 can accumulate these particles and avoid a blocking of the spindle 14. In case the valve is in an upright position as illustrated in the figure 1 , the cavity 28 can collect the particles from the second gasket 24 moving down by gravity. In case the valve would be in another orientation, e.g. with the spindle horizontal or downward, the cavity 28 can collect the particles from the first gasket 22. The cavity 12 ² formed in the movable closure member 12 permits also to collect the particles from the first gasket 22, in particular when the valve is in an upright position as illustrated in figure 1. The funnel-shaped opening 12 ³ of the cavity 12 ² is particularly useful for collecting the particles and prevent them from reaching the threaded engagement between the movable closure member 12 and the body 16.

[0046] Figure 2 is a magnified view of the area II in figure 1 , corresponding to the two gas tight barriers of the valve.

[0047] We can observe in figure 2 that the surface 14 ⁵ of shoulder 14 ² of the spindle 14 that contacts the first gasket 22 is not flat but rather is slightly bevelled. That surface 14 ⁵ is shaped so that its external portion is closer to the shoulder 18 ¹ of the body than its internal portion. The shoulder 18 ¹ of the body comprises also a circular rib 18 ⁴ that is intended to penetrate into the first gasket 22. This rib 18 ⁴ is positioned at an external circumferential portion of the shoulder 18 ¹ in order to be at least approximately aligned with the raised external portion of the shoulder 14 ² . The gasket 22 is therefore more stressed at its external portion so to be properly penetrated by the rib 18 ⁴ and provide an adequate first gas tight barrier.

[0048] We can also observe in figure 2 that a flared external surface 26 ¹ of the sleeve 26 that can abut against the corresponding external surface 18 ⁴ of the plug before the front end 26 ² contacting the gasket 24 would reach the bottom of the cavity of said gasket.

[0049] Still in figure 2 we can observe the shape of the second gasket 24 with a trapezoid cross-section. The larger base 24 ¹ is in contact with the external surface of the spindle 14 whereas the smaller base 24 ² is in contact with the internal surface of the plug 18. The larger base 24 ¹ can comprise a groove 24 ³ that provides some room for deformation of the gasket. The side or leg 24 ⁴ is in contact with the corresponding surfaces 26 ² of the sleeve 26 and the other opposite side or leg 24 ⁵ is in contact with the corresponding surfaces 18 ⁵ of the sleeve plug 18. The axial force exerted by the sleeve 26 via its contact surface 26 ² is converted into a radial force thanks to the inclination of the surfaces 26 ² and 18 ⁵ .

The different elements of the valve 2, like the main body 16, the plug 18, the spindle 14 and/or the movable closure element 12 can be made of brass, steel and/or stainless steel. Some elements, like the movable closure element 12 and/or the spindle 14 can be coated with Teflon® so as to lower the frictional forces.