GB2513008A

GB2513008A - Breathing and draining device

Info

Publication number: GB2513008A
Application number: GB1404780.7A
Authority: GB
Inventors: Kevin Fogarty; David Hope; Dave Thompson; Bob Birchmore
Original assignee: ICON SCIENT Ltd
Current assignee: ICON SCIENT Ltd
Priority date: 2013-03-15
Filing date: 2014-03-17
Publication date: 2014-10-15
Anticipated expiration: 2034-03-17
Also published as: GB201304700D0; GB201404780D0; GB2513008B

Abstract

A breathing and draining device 100, or flame arrester, is disclosed for use with an explosion-proof enclosure 1 housing a device for measuring properties of hydrocarbons. The flame arrester comprises an inlet 104 and an outlet 110 and a flow path from the inlet to the outlet. The flame arrester further comprises an inner body 102 and an outer housing 101. The inner body is located within the outer housing such that the flow path passes through a gap 105 between the inner body and the outer housing. The width of the gap is no greater than 2.0 mm across so as to restrict the travel of flames but sufficient to allow the passage of fluid between the inlet and the outlet. A first end of the inner body has an inlet in the form of a hollow threaded fitting 104 for forming a fluid-tight connection to another component of the enclosure 1. The hollow fitting 104 communicates with a hollow bore 107 in the inner body, which in turn communicates with an orifice 108. The orifice opens into an annular groove 118 around the inner body which, together with the outer housing, forms an annular chamber 109 before the start of the gap 105.

Description

Breathing and Draining Device

Field of the Invention

The present invention concerns a breathing and draining device. In particular, but not exclusively, the invention concerns a breathing and draining device for use in devices installed in explosive atmospheres in chemical plants or refineries.

Background ef the Invention

Measurements of hydrecarbon properties may be carried out in chemical plants such as refineries. The measurements can be carried out by taking a sample to a laboratory but doing so results in a delay in obtaining the data. A method of taking online measurements is therefore desirable. However, refineries often include zones with potentially explosive atmospheres so online measurements need to be safe for use in such zones. In particular, the measurement device should not be able to create a source of ignition that could ignite the surrounding atmosphere.

Measurement instruments can be contained in explosion-proof boxes, which are designed to withstand the force of an explosion in the measurement device without the box failing and therefore to contain such an event within the box. However, in order to perform an online measurement a sample drawn from a process line with a sampling line needs to get into the explosion-proof box. Also, once the measurement has been taken, the sample needs to exit the box so as to return to the process or be sent to waste.

It is known to attach sample lines to enclosures such as explosion-proof boxes and to fit a breathing and draining device, also known as a flame arrestor, where the sample line meets the enclosure. The breathing and draining device is typically a long tube filled with metal wool or metal mesh. The filling creates a tortuous path that is sufficiently long and narrow to prevent a flame travelling from one end to another.

While such devices are able to prevent flames travelling out of an enclosure along a sample line, they may be difficult to manufacture reproducibly and nay have a large pressure drop along their length. That can make it difficult to pump the sample through the breathing and draining device under normal operation of the instrument, particularly if the sample is a heavy hydrocarbon fraction.

U54785158 discloses a flame arrester with a tube welded to a rod at locations around the rod. The welds partially obstruct the flow path between the tube and the rod.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the prcscnt invontion socks to providc an improvod broathing and draining device.

Summary of the Invention

According to a first aspect of the invention, there is provided a breathing and draining device comprising an inlet and an outlet and a flow path from the inlet to the outlet, wherein the device comprises an inner body and an outer housing, wherein the inner body is located within the outer housing such that the flow path passes through a gap between the inner body and the cuter housing, wherein the gap is no greater than 2.0 rim across.

Thus there is provided a breathing and draining device made of two parts, configured so as to have a gap between them. The width of the gap (i.e. the distance across the gap) is chosen so as to restrict the passage of a flame through the gap. The two parts can be machined reliably and repeatably resulting in a breathing and draining device that can be manufactured consistently on a large scale. Moreover, because the flame is arrested in a gap, rather than in a tortuous path, the pressure drop through the device during normal use may be lower than for an eguivalently rated device made with a tortuous path. The flow path therefore allows the passage of fluid between the inlet and the outlet but restricts the travel of flames or sparks. When the flow path is said to pass through the gap, it will be understood that the gap between the inner body and the outer housing at least partly defines the flow path.

The gap may be important in determining the extent to which tho dcvicc can arrest a flame. Preferably thc gap is no greater than 2.0 mm across. More preferably the gap is no greater than 1.5 mm across. More preferably the gap is no greater than 1.0 mm across. More preferably the gap is no greater than 0.8 mm across. Even more preferably the gap is no greater than 0.5 mm across. The width of the gap may be defined as the spacing of the inner body and the outer housing across the gap. Thus the outer honising and the inner body may be spaced apart across the gap by no greater than 2.0 mm, preferably no greater than 1.5 mm, more preferably no greater than 1.0 mm, more preferably no greater than 0.8 mm and even more preferably no greater than 0.5 mm. Narrower gaps nay increase the ability of the device to arrest a flame, but may also increase the pressure drop and may reguire more precise manufacture of the inner body and the outer housing. Thus the gap is preferably no less than 0.1 mm across, more preferably no less than 0.2 mm across and even more preferably no less than 0.3 mm aoross. Such a minimum gap size may reduce the prospect of manufacturing abnormalities or surface unevenness causing the inner body and outer housing to come together, partially blocking the gap. Partial blockage of the gap may result in unnecessary increases in the pressure drop through the device. It may be that the surface roughness of the internal surface of the outer housing is no greater than 6.3 micrometres. It may that the surface roughness of the external surface of the inner body is no greater than 6.3 micrometres. The skilled person will appreciate that the internal surface of the outer housing and the external surface of the inner body are the two surfaces that bound the gap between the inner body and the outer housing. By restricting the surface roughness of those surfaces, a narrow gap can bo manufacturod with prccision.

Preferably the inner body is a solid body in that it has a substantially continuous outer surface. Preferably the inner body is a rigid body. Tn that way a uniform gap may be maintained across the length of the inner body. It will be appreciated that the solid body may be hollow in that it may have a hole bored through it, but the inner body is preferably not a mesh or wool. It may be that there is only one distinot flow path from the inlet to the outlet; in other words, it may be that the flow path S is not divided by any obstaoles. It may be that there are a small number, for example 10 or fewer, preferably 5 or fewer and more preferably 2 or fewer distinct flow paths from the inlet to the outlet. It may be that the flow path is not tortuous. For example, it may be that the flow path through the device comprises a flow path from inlet to outlet having 10 or fewer, preferably 5 or fewer and more preferably 2 or fewer changes in direotion.

Reducing the tortuosity of the path may reduce the pressure drop across the device for a given flame arresting capability.

Preferably the gap extends along greater than 50%, preferably greater than 60%, more preferably greater than 70%, more preferably greater than 80% and more preferably greater than 90% of the length of the flow path.

Preferably the gap is a uniform gap. Preferably the flow path passes through the gap in a straight line.

Preferably the flow path passes through the gap in a lengthwise direction relative to the inner body.

Preferably the inner body and the outer housing are rigid bodios and tho gap oxtonds circumforontially around tho outer surface of the inner body and lengthwise along the inner body. By providing two rigid bodies with a uniform gap between the bodies and extending along the bodies with the flow path passing through the gap in the lengthwise direction the heat of a flame is passed to the rigid bodies and the length and width of the gap can be chosen so that enough energy is removed from the flame as it passes along the length of the gap. Because the gap is uniform the flame arresting is uniform across the gap and because the flow path passes through the gap in a single, lengthwise direction there are no shorter or longer paths through the gap so the pressure drop may be minimised.

Preferably the inner body comprises a first cylinder and the outer housing comprises a second, hollow cylinder and the inner body is located within the outer housing such as to form an annular gap between the first and second cylinders. For example, it may be that the outer housing is mounted on the inner body such as to form an annular gap between the first and second cylinders.

cylinders may be advantageous in that cylinders may be easy to machine with the necessary levels of precision.

Moreover, the outer housing and the inner body may each comprise threads such that the outer housing is threadedly mountable on the inner body. A threaded mounting may advantageously provide a quick but secure method of mounting the outer housing on the inner body.

Alternatively the inner body may comprise an outward mounting surface and the outer housing may comprise an inward mounting surface sized so as to engage with the outward mounting surface when the outer housing is slid onto the inner body thus ensuring alignment of the outer body with tho innor housing. It will bo undorstood that an outward mounting surface is a mounting surface that faces substantially radially outwards, whilst an inward mounting surface is a surface that faces substantially radially inwards. The inward and outward mounting surfaces are preferably smooth surfaces. Such an arrangement may advantageously permit tighter manufacturing tolerances than a threaded mounting, and may therefore allow for more reliable manufacture of devices with long gaps. The outer housing may be welded to the inner body in the region of a first end of the inward mounting surface. The weld is preferably a circumferential weld. Such a weld advantageously prevents accidental removal of the outer housing from the inner body and may provide an improved seal between the cuter housing and the inner body so that there is no flow path between the mounting surfaces and the only flow path is through the gap.

Preferably the inner body comprises a hollow fitting at a first end for creating a fluid-tight connection to another component. The hollow fitting may form the inlet of the device. Preferably, in use, the inlet is placed towards the direction from which a flame may approach.

Preferably the inner body comprises an orifice, preferably a radial orifice, allowing fluid communication between the hollow fitting and the gap. For example, the inner body may comprise a first cylinder, a first fitting, preferably threaded, at a first end of the first cylinder for creating a fluid-tight connection to another component, a second fitting, preferably threaded, spaced apart from the first fitting along the length of the first cylinder, a hollow space along the centre of the inncr body oxtonding from tho first ond to boyond tho second fitting and an orifice extending from the hollow space, through the first cylinder to the outer surface of the first cylinder. The device may then comprise an outer housing comprising a hollow second cylinder, wherein the outer housing comprises an internal fitting, preferably a thread, corresponding to the second fitting and the second cylinder is sized such that, when the second cylinder is mounted on the inner body with the internal fitting engaged with the second fitting, an annular gap not greater than 2.0 mm across is formed between the first cylinder and the second cylinder and extending from the fittings toward a second end of the first cylinder, opposite to the first end, and the orifice extends from the hollow space to the gap.

Tt may be that the inner body comprises a first cylinder, a first fitting, preferably threaded, at a first end of the first cylinder for creating a fluid-tight connection to another component, an outward mounting surface, preferably a smooth cylindrical surface, spaced apart from the first fitting along the length of the first cylinder, a hollow space along the centre of the inner body extending from the first end to beyond the outward mounting surface and an orifice extending from the hollow space, through the first cylinder to the outer surface of the first cylinder. The device may then comprise an outer housing comprising a hollow second cylinder, wherein the outer housing comprises an inward mounting surface, preferably a smooth cylindrical surface, corresponding to the outward mounting surface and the second cylinder is sized such that, when the second cylinder is mounted on the inner body with the inward mounting surface engaged with the outward mounting surface, an annular gap not greater than 2.0 mm across is formed between the first cylinder and the second cylinder and extending from the mounting surfaces toward the second end of the first cylinder, opposite to the first end, and the orifice extends from the hollow space to the annillar gap. It may be that the outward mounting surface engages with the inward nounting surface such that there is substantially no gap between the mounting surfaces such that the only flow path through the device passes via the orifice and the annular gap. Preferably the outer housing is welded to the inner body at the end of the mounting surfaces nearest to the first end of the first cylinder. That is, the weld may be at the end of the mounting surfaces away from the annular gap. Thus the weld does not interfere with, or partially block, the annular gap. The weld may be a circumferential weld. A circumferential weld may provide a further seal that prevents flow out of the device between the two mounting surfaces. It may be that the mounting surfaces are welded together. It may be that the first cylinder comprises a stop section between the first fitting and the outward mounting surface, the stop section having a greater radius than the mounting surface, and the outer housing butts against the end of the stop section away from the first end of the cylinder and is welded to that end of the stop section. The radius of the stop section may be equal to the outer radius of the outer housing.

The end of the outer housing and the end of the stop section that are adjacent to each other may each comprise a chamfer, for example a chamfer having a depth of 0.5 to 2 mm, for example 1 mm, and an angle of between 20 and 40 degrees, for example 30 degrees. The two chamfers may thus provide a circumferential groovo where the outer housing butts against the stop section and the weld may be a circumferential weld around that circumferential groove.

It may be that the first cylinder has a smaller diameter in the region of the orifice such that the -10 -orifice opens into an annular groove in the first cylinder, with the annular gap starting at the edge of the groove away from the first end of the device.

Preferably the annular gap has a substantially uniform width around the oylinder of the inner body; that is around the first cylinder. Preferably the annular gap has a substantially uniform width along the cylinder of the inner body; that is along the first cylinder. A substantially uniform gap may advantageously result in a more uniform flow profile through the gap and reduce the likelihood of high local stresses on part of the device.

Tt may be that the outer housing extends beyond the inner body and the part of the outer housing extending beyond the inner body comprises a fitting for forning a fluid-tight connection to another component. For example, that fitting may be the outlet. For example, the hollow cylinder of the outer housing, the second cylinder, may extend beyond the second end of the cylinder of the inner body, the first cylinder, and the inside of the second end of the hollow, second, cylinder may comprise a thread for forming a fluid-tight connection to another component.

Tt may be that the outer surface of the outer housing, including of cylindrical outer housings, includos flattcncd soctions suitablc for ongaging with a wrench. It will be understood that the flattened sections only affect the outer surface and that the inner surface of the outer housing would remain cylindrical.

It will be understood that the device is suitable for use in potentially explosive environments. For -11 -example, the device may be rated in the following gas groups arid temperatures classes: hA 12, hA T3, IIB 13, TIE + H2 T4, T85°C for Dust only environments or 1300°C.

The device may comply with standards IEC 60079-0: 2007-hO S Explosive atmospheres -Part 0: Equipment -General requirements, IEC 60079-1: 2007-04 Explosive atmospheres -Part 1: Equipment protection by flameproof enclosures "d" and IEC 60079-31: 2008 Explosive atmospheres -Part 31: Equipment dust ignition protection by enclosure \t".

The device may provide equivalent or better explosion-proof testing performance and transmission testing performance as devices according to those standards.

In some embodiments the length of the gap is preferably in the range 150 -to 200 mm, more preferably in the range 160 mm to 190 inn, and even more preferably in the range 170 mm to 180 inn. For example the length of the gap may be 175 mm +0.5 inm/ -0.0 mm. That is, the gap may be in the range 175.0 mm to 175.5 mm. In such embodiments it may be that the width of the gap is, for example, not greater than 0.5 mm. Such a gap length and width may provide reliable flame arresting for 113 + H2 14 applications while having a satisfactory pressure drop.

Tn some embodiments the length of the gap is preferably in the range 100 mm to 115 mm and more prcfcrably in thc rangc 105 mm to 110 mm. For cxanplc tho length of the gap may be 107 mm +0.5 mm/ -0.0 mm. That is, the gap may be in the range 107.0 mm to 107.5 mm. In such embodiments it may be that the width of the gap is, for example, not greater than 1.5 mm, or not greater than 1.0 mm, or even not greater than 0.8 mm. Such a gap length and widths may provide reliable flame arresting -12 -for ISA 12, hA 13 and IIB 13 applications respectively while having a satisfactory pressure drop.

It will be appreciated that the length of the gap is the shortest length of the gap along the flow path through the device. It may be that the shortest length of the gap along the flow path through the device is sufficiently long to provide adeguate flame arrest in the prevailing atmospheric conditions. It may be that the width and length of the gap are selected so as to provide adeguate flame arrest in the design conditions, whilst maintaining a pressure drop across the device within a satisfactory range. The gap may extend along more than half the length of the device.

Preferably the device is a two-way device in that the device will operate with flow from the inlet to the outlet or from the outlet to the inlet. It may be that, in use, the direction from which a flame is likely to approach is opposite to the flow direction in nornal use; for example, the inlet may be placed towards the direction from which a flame would approach, but flow conditions in normal use may be flow from the outlet to the inlet.

Advantageously the device is used to facilitate the provision of samplos to an instrumont locatod within an explosion-proof enclosure. In that way, automated measurements can be made online in hazardous environments, such as potentially explosive atmospheres, for example in oil refineries or chemical plants. Thus an instrument may be provided within an explosion-proof housing, such as an explosion-proof box, that is provided -13 -with one or more of the devices. The skilled person will appreciate that an explosion-proof housing is one that prevents potential ignition sources, such as sparks, flames or explosions, within the box escaping to the outside environment.

For example, the explosion-proof housing may be rated in the following gas groups and temperatures classes: hA 12, hA T3, IIB 13, fIB + H2 14, T85°C for Dust only environments or T300°C. The explosion-proof housing may comply with standards lEO 60079-0: 2007-10 Explosive atmospheres -Part 0: Equipment -General reguirements, lEO 60079-1: 2007-04 Explosive atmospheres -Part 1: Eguipment protection by flameproof enclosures d" and lEO 60079-31: 2008 Explosive atmospheres -Part 31: Eguipment dust ignition protection by enclosure "t".

Thus, according to a second aspect of the invention there is provided an apparatus for measuring a property of a hydrocarbon, for example a hydrocarbon liguid, the apparatus comprising an explosion-proof housing, wherein the explosion-proof housing comprises a sample inlet port comprising a breathing and draining device according to the first aspect of the invention, the apparatus further comprising an instrument configured to measure the property, the instrument being located within the oxplosion-proof housing and boing fluidly connoctod to the sample inlet port to allow a sample entering the explosion-proof housing through the inlet to be fed to the instrument. Preferably the explosion-proof housing further comprises an outlet port comprising a breathing and draining device according to the first aspect of the invention and the instrument is fluidly connected to the -14 -outlet port to allow a sample that has been measured in the instrument to exit the explosion-proof housing. In some embodiments the instrument may require a utility, such as steam. Thus, in some embodiments, there is preferably provided a utility port comprising a breathing and draining device according to the first aspect of the invention and the instrument is fluidly connected to the utility port to allow provision of the utility to the instrument. The property being measured may, for example, be the pour point, the flash point, the freeze point, the cloud point, the cold filter plugging point or the vapour pressure.

Preferably the shortest length of the gap along the flow path through the device and the width of the gap are sufficient to provide adequate flame arrest in the conditions in which the apparatus is to be used.

It may be that there is provided an apparatus for measuring a property of a sample, for example a hydrocarbon, preferably a liquid hydrocarbon, sample, the apparatus comprising an explosion-proof housing comprising a port, wherein the port comprises a breathing and draining device according to the first aspect of the invention. The port may for example be an inlet, outlet or utility port and may be fluidly conneoted to an instrumont insido tho housing for moasuring thc propcrty.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the second aspect of the invention may incorporate any of the features described -15 -with reference to the first aspect of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 is a front view of an apparatus according to an embodiment of the invention; Figure 2 is a side view of the apparatus of Figure 1; Figure 3 is a perspective view of a breathing and draining device according to a second embodiment of the invention; Figure 4 is a side view of the device of figure 3; Figure 5 is a cut-away view of the device of figure 3; Figure 6 is a perspective view of the outer housing of the device of figure 3; Figure 7 is a side view of the outer housing of figure 6; Figure 8 is a cut-away view of the housing of figure 6; Figure 9 is a perspective view of the inner body of the device of figure 3; Figure 10 is a side view of the inner body of figure 9; Figure 11 is a close-up of part of the side view of figure 10; Figure 12 is a cut-away view of the inner body of figure 9 Figure 13 is a perspective view of a breathing and draining device according to a third embodiment of the invention; -16 -Figure 14 is a cut-away view of the device of figure 13; Figure 15 is a perspective view of the outer housing of the device of figure 13; Figure 16 is a cut-away view of the housing of figure 15; Figure 17 is a perspective view of the inner body of the device of figure 13; Figure 18 is a side view of the inner body of figllre 17; Figure 19 is a close-up of part of the side view of figure 18; and Figure 20 is a cut-away view of the inner body of figure 17.

Detailed Description

In figure 1 an instrument is contained within an explosion-proof housing in the form of an explosion-proof box 1. The box 1 is mounted on a stand 2 on which there is mounted a second explosion-proof box 3. The box 3 is mounted above the box 1 with a 40 mm separation between the boxes. On the front of the box 3 there is a touch screen 4. The fronts of boxes 1 and 3 are mounted on hinges 5a,b and 6a,b respectively so that the fronts of the boxes 1 and 3 can pivot through 180° to open the boxes 1 and 3.

In figure 2 breathing and draining devices 7 and 8 are mounted on the back of box 1. Communication cable 9 connects boxes 1 and 3 so as to allow data and power transfer between the various electronic devices within the boxes 1 and 3. Boxes 1 and 3 have external enclosure -17 -earth bolts 10 and 11 mounted on them to earth the boxes 1 and 3. Earth stud 12 is mounted on frame 2.

In figures 3, 4 and 5 a breathing and draining S device 100 has an inner body 102 and an outer housing 101. The outer housing 101 is screwed onto the inner body 102 and held in place by grub screws 103. A sealant may be used with the grub screws 103 to seal the thread. A first end of the inner body 102 has an inlet in the form of threaded fitting 104 for forming a fluid-tight connection to another component such as a sample input port in the box 1. The fitting 104 is hollow. There is an annular gap 105 between the inner body 102 and the outer housing 101. In this embodiment the gap is no greater than 1.0 mm across. The outer housing 101 extends beyond the second end 106 of the inner body 102. The hollow fitting 104 communicates with a hollow bore 107 in the inner body 102, which in turn communicates with an orifice 108. The orifice opens into an annular groove around the inner body 102 which, together with the outer housing 101, forms an annular chamber 109 before the start of the gap 105. At the second end of the device there is an outlet 110. The outer housing 101 has an inner surface roughness of 6.3 micrometres and the inner body 102 has a surface roughness of 6.3 micrometres. The device 100 is made from stainless steel 316 or 304. Sharp odgos aro doburrod and brokon.

In figures 6, 7 and 8 the outer housing 101 has a hole 111 to receive the grub screw 103. In figure 8, the outer housing 101 has a first section 112 with a first diameter, a second section 113 with a second diameter, part of which forms the outside of the grove 105 and a -18 -third section 114 with a third diameter that forms a fitting for forming a fluid-tight connection to another component. Tn this embodiment, the length of the outer housing 101 is 156 mm, the outer diameter is 30 mm and the diameter of the hole U is 2.5 mm. The diameter of the first section 112 is 25 mm and of the second section 113 is 20 mm. The diameter of the second section 113 is machined to an accuracy of ÷/-0.0O mm. The third section 114 has a 1/2 National Pipe Thread Taper (NPT) . The first section 112 extends 20 mm from the first end of the outer housing and the second section extends from the end of the first seotion to a distance of 136 mm from the first end of the outer housing. The latter dimension is machined to within +1/-0.5 mm.

Tn figures 9, 10, 11 and 12, the inner body 102 comprises a cylinder 115. There is an annular grove 118 at the end of the cylinder 115 toward the first end of the body 102. Beyond the annular groove 118 there is a thread 117 and beyond that, at the first end of the body 102 there is a threaded fitting 104. The threaded fitting 104 is hollow and communicates with the hollow bore 107 up the centre of the body 102. The bore 107 communicates with a radial orifice 108, which opens into the annular groove 118. In this embodiment the threaded fitting 104 has a length of 35 mm and the thread 117 has a length of 19 mm and is soparatod from tho throadcd fitting 104 by a distance of 10 nun. The annular groove 118 spans a length of 5 mm and the orifice 108 opening into it has a 3.5 mm diameter. The cylinder extends 107 mm +0.5/-0.0 mm from the annular groove and the overall length of the body is 176 mm. The cylinder diameter is 19 mm +0.1/-0.0 mm and the diameter in the annular groove 118 is 18 mm. The -19 -largest diameter of the body, which is the section between the threaded fitting 104 and the thread 117, is 28 mm. The diameter of the bore 107 is 7 mm.

In use the cuter housing 101 is screwed onto the inner body 102 so that the thread 117 engages with the first section 112. Fluid enters through the inlet hollow in the threaded fitting 104, which is attached to another component, and flows along the bore 107 and through the orifice 108. The fluid exits the orifice 108 into the chamber 109 formed between the annular groove 118 and the seccnd section 113. The fluid then flcws thrcugh the annular gap 105 formed between the second section 112 and the cylinder 115. The annular gap 105 has a width of 1.0 mm and a length of 107 mm and permits flow of the fluid but arrests flames that may try to travel along the gap 105. The length and width of the gap 105 are sufficient to arrest flames in hA T3 applications. On exiting the gap 105, the fluid flows through the third, outlet section 114, which is connected to further components.

Thus the flow path through the device consists of the hollow fitting 104, the bore 107, the orifice 108, the chamber 109, the annular gap 105 and the outlet section 114. The flow path is a single, distinct flow path in that the path is undivided with no branches. It will be appreciated that the device 100 can be used as either an input or an output dovico and that tho flow can occur in either direction.

In figures 13 and 14 a breathing and draining device has an inner body 202 and an outer housing 201. The outer housing 201 is mounted onto the inner body 202 and held in place by a circumferential weld 203. A first end -20 -of the inner body 202 has an inlet in the form of threaded fitting 204 for forming a fluid-tight connection to another component such as a sample input port in the box 1. The fitting 204 is hollow. There is an annular gap 205 between the inner body 202 and the outer housing 201.

In this embodiment the gap is no greater than 0.8 mm across. The outer housing 201 extends beyond the second end 206 of the inner body 202. The hollow fitting 204 communicates with a hollow bore 207 in the inner body 202, which in turn communicates with an orifice 208. The orifice 208 opens into an annular groove around the inner body 202 which, together with the outer hoilsing 201, forms an annular chamber 209 before the start of the gap 205. At the second end of the device there is an outlet 210. The outer housing 201 has an inner surface roughness of 6.3 micrometres and the inner body 202 has a surface roughness of 6.3 micrometres. The device 200 is made from stainless steel 316 or 304. Sharp edges are deburred and broken. The outer housing 201 has flattened sections 222 on opposing sides of its outer surface so as to enable engagement by a wrench. The flattened sections 222 do not extend through to the inner surface of the outer housing 201, which remains cylindrical.

Tn figures 15 and 16 the outer housing 201 has a first section 212 with a first diameter, a second section 113 with a second diameter, part of which forms the outside of the grove 205 and a third section 214 with a third diameter that forms a fitting for forming a fluid-tight connection to another component. In this embodiment, the length of the outer housing 201 is 156 mm, the outer diameter is 30 mm. The diameter of the first section 212 is 23 mm and of the second section 213 -21 -is 20 mm. The diameter of the second section 213 is machined to an accuracy of -i-/-0.00 mm. The third section 214 has a 1/2 National Pipe Thread Taper (NPT) . The first section 212 extends 20 mm from the first end of the cuter housing and forms a smooth inward mounting surface. The left hand end of the first section 212 is chamfered on the outer edge. The second section 213 extends from the end of the first section 212 to a distance of 136 mm from the first end of the outer housing. The latter dimension is machined to within +1/-0.5 mm.

In figures 17, 18, 19 and 20, the inner body 202 comprises a cylinder 215. There is an annular grove 218 at the end of the cylinder 215 toward the first end of the body 202. Beyond the annular groove 218 there is a smooth outward mounting surface 217 and beyond that, at the first end of the body 202 there is a threaded fitting 204. The threaded fitting 204 is hollow and communicates with the hollow bore 207 up the centre of the body 202.

The bore 207 communicates with a radial orifice 208, which opens into the annular groove 218. In this embodiment the threaded fitting 204 has a length of 35 mm and the outward mounting surface 217 has a length of 19 mm and is separated from the threaded fitting 204 by a distance of 10 mm. The annular groove 218 spans a length of 5 mm and the orifice 208 opening into it has a 3.5 mm diamotor. Tho cylindor oxtonds 107 mm +0.5/-0.0 mm from the annular groove and the overall length of the body is 176 mm. The cylinder diameter is 19.2 mm and the diameter in the annular groove 218 is 18 mm. The largest diameter of the body, which is the stop section 220 between the threaded fitting 204 and the outward mounting surface -22 - 217, is 30 ruin. The diameter of the bore 207 is 7 ram. The right hand end of the stop seotion 220 is ohamfered.

To manufacture the device 200 the outer housing 201 is slid onto the inner body 202 so that the outward mounting surface 217 engages with the inward mounting surface of the first section 212. The outer housing 201 is welded to the inner body 202 by means of the circumferential weld 203 in the groove formed between the chamfered ends of the first section 212 and the stop section 220.

Tn use, fluid enters through the inlet hollow in the threaded fitting 204, which is attached to another component, and flows along the bore 207 and through the orifice 208. The fluid exits the orifice 208 into the chamber 209 formed between the annular groove 218 and the second section 213. The fluid then flows through the annular gap 205 formed between the second section 212 and the cylinder 215. The annular gap 205 has a width of 0.8 mm and a length of 107 rum and permits flow of the fluid but arrests flames that may try to travel along the gap 105. The length and width of the gap 105 are sufficient to arrest flames in Group P T3 applications. On exiting the gap 205, the fluid flows through the third, outlet section 214, which is connected to further components.

Thus tho flow path through tho dovico consists of tho hollow fitting 204, the bore 207, the orifice 208, the chamber 209, the annular gap 205 and the outlet section 214. The flow path is a single, distinct flow path in that the path is undivided with no branches. It will be appreciated that the device 200 can be used as either an -23 -input or an output device and that the flow can occur in either direction.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

For example, in some embodiments the gap 105 is 1.5 mm across and 107 mm long. Such embodiments are suitable for hA 12 applications. In some embodiments, which are suitable for lIB 13 applications, the gap is 0.8 mm across and 107 mm long and in some embodiments, which are suitable for hIB + H2 T4 applications, the gap is 0.5 mm wide and 175 mm long.

Tn some embodiments there may be a small number of distinct flow paths. For example, there may be more than one orifice 108 connecting the bore 107 to the chamber 109. For example there may be four orifices spaced at 90° around the inner body 102. In that case there would be four distinct flow paths.

Whoro in tho forogoing dcscription, intogors or elements are mentioned which have known, obvious or foreseeable eguivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be -24 -appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-25 -Claims l.A breathing and draining device comprising an inlet and an outlet and a flow path from the inlet to the outlet, wherein the device comprises an inner body and an outer housing, wherein the inner body is located within the outer housing such that the flow path passes through a gap between the inner body and the outer housing, wherein the gap is no greater than 2.0 mm across.
2. A breathing and draining device aocording to claim 1, wherein the gap is no less than 0.1 mm across.
3. A breathing and draining device according to claim 1 or claim 2, wherein the surface roughness of the inner surface of the outer housing is no greater than 6.3 micrometres.
4. A breathing and draining device according to any preceding claim, wherein the surface roughness of the outer surface of the inner body is no greater than 6.3 micrometres.
5. A breathing and draining device according to any preceding claim, wherein the inlet comprises a hollow fitting at a first end of the inner body for creating a fluid-tight connection to another component and the inner body comprises an orifice allowing fluid communication between the hollow fitting and the gap.
6. A breathing and draining device according to any preceding claim, wherein the inner body comprises a first cylinder and the outer housing comprises a second, hollow cylinder and the inner body is located within the outer housing as to form an annular gap between the first and second cylinders.

-26 -
7. A breathing and draining device according to claim 6, wherein the outer housing and the inner body each comprise threads such that the outer housing is threadedly mountable on the inner body, so as to locate the inner body within the outer housing.
8. A breathing and draining device according to claim 6, wherein the inner body comprises an outward mounting surface and the outer housing comprises an inward mounting surface sized so as to engage with the outward mounting surface when the outer housing is slid onto the inner body thus ensuring alignment of the outer body with the inner housing.
9. A breathing and draining device according to claim 8 wherein the outer housing is secured to the inner housing by a circumferential weld in the region of the mounting surfaces and away from the annular gap.
10. A breathing and draining device according to any preceding claim, wherein the inner body comprises: a. a first cylinder, b. a first threaded fitting at a first end of the first cylinder for creating a fluid-tight connection to another component, c. a second threaded fitting spaced apart from the first threaded fitting along the length of the first cylinder, d. a hollow spacc along the contrc of thc inner body extending from the first end to beyond the second threaded fitting, and e. an orifice extending from the hollow space, through the first cylinder to the outer surface of the first cylinder, and wherein the outer housing comprises: -27 -f. a second, hollow cylinder, and g. an internal thread corresponding to the second threaded fitting wherein the second cylinder is sized such that, when the second cylinder is mounted on the inner body with the internal thread engaged with the second threaded fitting, an annular gap not greater than 2.0 mm across is formed between the first cylinder and the second cylinder and extending from the fittings toward a second end of the first cylinder, opposite to the first end, and the orifice extends from the hollow space to the annular gap.
II. A breathing and draining device according to any of claims 1 to 9, wherein the inner body comprises: a. a first cylinder, b. a first fitting at a first end of the first cylinder for creating a fluid-tight connection to another component, c. an outward mounting surface spaced apart from the first fitting along the length of the first cylinder, d. a hollow space along the centre of the inner body extending from the first end to beyond the outward mounting surface and e. an orifice extending from the hollow space, through tho first cylindor to the outor surface of the first cylinder, and wherein the outer housing comprises: f. a second, hollow cylinder, and g. an inward mounting surface corresponding to the outward mounting surface -28 -wherein the second cylinder is sized such that, when the second cylinder is mounted on the inner body with the inward mounting surface engaged with the outward mounting surface, an annular gap not greater than 2.0 mm across is formed between the first cylinder and the second cylinder and extending from the mounting surfaces toward a second end of the first cylinder, opposite to the first end, and the orifioe extends from the hollow spaoe to the annular gap.
12. A breathing and draining device according to claim 11 wherein the outward mounting surface engages with the inward mounting surface such that there is substantially no gap between the mounting surfaces such that the only flow path through the device passes via the orifice and the annular gap.
13. A breathing and draining device according to claim 11 or claim 12 wherein the outer housing is welded to the inner body at the end of the mounting surfaces nearest to the first end of the first cylinder.
14. A breathing and draining device according to claim 13 wherein the first cylinder comprises a stop section between the first fitting and the outward mounting surface, the stop section having a greater radius than the mounting surface, and the outer housing butts against tbc cnd of thc stop section away from the first end of the cylinder and is welded to that end of the stop section.
15. A breathing and draining device according to claim 14 wherein the end of the outer housing and the end of the stop section that are adjacent to each other each oomprise a chamfer and the two -29 -chamfers provide a circumferential groove where the outer housing butts against the stop section and the weld is a circumferential weld around the circumferential groove.
16. A breathing and draining device according to any of claims 6 to 15, wherein the annular gap has a substantially uniform width around the first cylinder.
17. A breathing and draining device according to any of claims 6 to 16, wherein the annular gap has a substantially uniform width along the first cylinder.
18. A breathing and draining device according to any preceding claim, wherein the outer housing extends beyond the inner body and the outlet comprises a fitting for forming a fluid-tight connection to another component, the fitting being comprised in the part of the outer housing extending beyond the inner body.
19. A breathing and draining device according to any preceding claim, wherein the length of the gap is in the range 150 mm to 200 mm.
20. A breathing and draining device according to any of claims 1 to 18, wherein the length of the gap is in the range 100 mm to 115 mm.
21. A breathing and draining device substantially as horoin doscribod with roforonco to any of tho accompanying drawings.
22. Au apparatus for measuring a property of a hydrocarbon, the apparatus comprising an explosion-proof housing, wherein the explosion-proof housing comprises a sample inlet port comprising a breathing and draining device according to any preceding -30 -claim, the apparatus further comprising an instrument configured to measure the property, the instrument being located within the explosion-proof housing and being fluidly connected to the sample inlet port to allow a sample entering the explosion-proof housing through the inlet to be fed to the instrument.
23. An apparatus according to claim 22 wherein the explosion-proof housing further comprises an outlet port comprising a breathing and draining device according to any of claims 1 to 21 and the instrument is fluidly oonnected to the outlet port to allow a sample that has been measured in the instrument to exit the explosion-proof housing.
24. An apparatus acoording to claim 22 or claim 23, wherein the explosion-proof housing further comprises a utility port comprising a breathing and draining device according to any of claims 1 to 21 and the instrument is fluidly conneoted to the utility port to allow provision of a utility to the instrument.
25. An apparatus for measuring a property of a hydrocarbon substantially as herein described with reference to any of the accompanying drawings.