Seal assembly for creating a sealed flow path between first and second fluid ducts

Abstract

A sealing assembly creating a sealed flow path between fluid ducts. The seal assembly comprises a housing and a tubular element within the housing providing a fluid conduit between the fluid ducts. Two sealing elements each have an internal sealing face sealably engaged with the tube and an external face for sealing, in use, with a respective fluid duct. At least one of the sealing elements is slidable with respect to the tubes. A support is slidably retained by the housing, surrounds one end of the tube and supports one of the slidable sealing elements on the side of the sealing element opposite to its external face. A resilient element within the housing biases the support so as to urge the two sealing elements apart.

Claims

1. A sealing assembly creating a sealed flow path between first and second fluid ducts, the sealing assembly having a first end facing the first fluid duct and a second end facing the second fluid duct; a housing; a tube having an axis and being within the housing providing a fluid conduit between the fluid ducts; a first sealing element at the first end having an internal sealing face slidably engaged with and slidable with respect to the tube and an external face substantially perpendicular to the axis of the tube for sealing, in use, with the first fluid duct; a second sealing element at the second end having an internal sealing face slidably engaged with and slidable with respect to the tube and an external face substantially perpendicular to the axis of the tube for sealing, in use, with the second fluid duct; a first support slidably retained by the housing and surrounding one end of the tube and supporting one of the first and second sealing elements on a side of the one of the first and second sealing elements opposite to its external face; and a resilient element within the housing biasing the support so as to urge the first and second sealing elements apart.

2. The sealing assembly according to claim 1, further comprising a second support surrounding an opposite end of the tube and supporting the other one of the first and second sealing elements on a side opposite to the external face of the other one of the first and second sealing elements, the resilient element being arranged to bias the first and second supports apart.

3. The sealing assembly according to claim 1, wherein each of the first and second sealing elements is configured such that when, in use, its external face is sealed against a respective one of the first and second fluid ducts, at least 60% of a perimeter of the seal is constrained directly by the one of the first and second fluid ducts, the housing, the first support and tube.

4. The sealing assembly according to claim 1, wherein, in cross-section, an angle of interface between the seal and the first support with respect to an axis of the tube is between 30 and 60.

5. The sealing assembly according to claim 1, wherein the tube comprises glass.

6. The sealing assembly according to claim 1, wherein the first and second sealing elements have a Young's Modulus of greater than 0.1 GPa.

7. The sealing assembly according to claim 6, wherein the first and second sealing elements have a Young's Modulus of between 0.2 GPa and 20 GPa.

8. The sealing assembly according to claim 1, wherein the first and second sealing elements are formed from a material selected from the group consisting of PFA, FEP, modified PTFE, and PEEK.

9. The sealing assembly according to claim 1, wherein the resilient element is a single compression spring.

10. The sealing assembly according to claim 1, wherein the external face of one or more of the first and second sealing elements has a raised annular portion.

11. The sealing assembly according to claim 1, wherein each of the first and second sealing elements is configured such that when, in use, its external face is sealed against a respective one of the first and second fluid ducts, at least 65% of a perimeter of the seal is constrained directly by the one of the first and second fluid ducts, the housing, the first support and tube.

12. The sealing assembly according to claim 1, wherein each of the first and second sealing elements is configured such that when, in use, its external face is sealed against a respective one of the first and second fluid ducts, at least 70% of a perimeter of the seal is constrained directly by the one of the first and second fluid ducts, the housing, the first support and tube.

13. A sealing assembly creating a sealed flow path between first and second fluid ducts, the sealing assembly having a first end facing the first fluid duct and a second end facing the second fluid duct; a housing; a tube within the housing providing a fluid conduit between the fluid ducts; a first sealing element at the first end having an internal sealing face slidably engaged with and slidable with respect to the tube and an external face for sealing, in use, with the first fluid duct; a second sealing element at the second end having an internal sealing face slidably engaged with and slidable with respect to the tube and an external face for sealing, in use, with the second fluid duct; wherein the tube does not protrude outwardly beyond the first and second sealing elements; a first support slidably retained by the housing and surrounding one end of the tube and supporting one of the first and second sealing elements on a side of the one of the first and second sealing elements opposite to its external face; and a resilient element within the housing biasing the support so as to urge the first and second sealing elements apart.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An example of a seal assembly and flow reactor in accordance with the present invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic cross-section of a flow reactor in accordance with the prior art and the present invention;

(3) FIG. 2 is a similar view of a modular reactor in accordance with the prior art and the present invention;

(4) FIG. 3 is an end view of a seal assembly according to the present invention;

(5) FIG. 4 is a cross-section through line IV-IV in FIG. 3;

(6) FIG. 5 is a view similar to FIG. 4 showing the components in an unstressed configuration;

(7) FIG. 6 is a view similar to FIG. 5 when clamped between the first and second fluid ducts;

(8) FIG. 7 is a schematic cross-section through a portion of the sealing element showing forces applied to the seal;

(9) FIG. 8 is a view similar to FIG. 6 showing a second example of a sealing assembly; and

(10) FIG. 9 is a view similar to FIGS. 6 and 8 showing a third example of the sealing assembly.

DETAILED DESCRIPTION

(11) Sealing assemblies of the present invention will be described below with reference to FIGS. 3 to 9. Any of these are suitable for use as the sprung seal 120 above in relation to FIGS. 1 and 2. The seal assembly is primarily designed for a reactor of the type described with reference to FIGS. 1 and 2. However, it can be used in any application where there is a desire to seal between first and second fluid ducts as described above.

(12) A first example of a seal assembly is shown in FIGS. 3 to 7.

(13) The assembly comprises a housing 200 which has a generally hollow cylindrical configuration. The housing comprises a base 202 and a cap 204 which are joined by a screw thread connection 206. The base 202 has a circular end wall 208 and the cap 204 has a corresponding circular end wall 210. The circular end wall 208 is provided with two through orifices 212 to prevent an air lock within the housing 200. These orifices 212 could equally or additionally be provided in the end wall 210 of the cap 204. Each of the end walls 208, 210 is provided with a central aperture 214, 216 having a frustoconical shape.

(14) Within the housing 200 are the remaining components of the seal assembly. These include a glass tube 220 forming the fluid duct through the centre of the housing 200, a helical spring 222 which is positioned between end plates 224 and 226 which are forced against the end faces 208, 210 respectively by the helical spring 222. At each end of the housing 200 is a sealing element 228, 230 surrounding the end of the glass tube 220.

(15) In order to assemble the seal assembly, the spring 222 and the end plates 224 and 226 are inserted into the base 202 and the end cap 204 is screwed in place. The glass tube 220 is then put into place and the two sealing elements 228 and 230 are pushed into position between the glass tube 220 and the respective end plates 224, 226 to form an interference fit. Alternatively, the glass tube 220 and sealing elements 228, 230 may be put in place before the end cap 204 is screwed into place.

(16) The seal assembly in its uncompressed state is shown in FIG. 5. As shown here, the spring 222 urges the end plates 224, 226 against the respective end walls 208, 210.

(17) When the seal assembly is in use between first fluid duct 240 and a second fluid duct 242, the ducts are brought together by a flange clamp 122 (FIG. 2) to the extent shown in FIG. 6 in which they compress the spring 222 thereby moving the end plates 224 and 226 away from the corresponding end walls 208, 210.

(18) As these plates 224, 226 move away from their respective walls 208, 210, the sealing elements 228, 230 slide along the glass tube 220 whilst, at the same time, being compressed to a small extent. As can be seen in FIG. 6, the housing 200 does not contact the first 240 or second 242 fluid ducts. The only contact between the sealing assembly and the fluid ducts 240, 242 is via the sealing elements 228, 230.

(19) Also apparent from FIG. 6 is the fact that the glass tube 220 provides a simple transition between the first 240 and second 242 fluid ducts with little or no dead space.

(20) The operation of the seal is shown in greater detail in FIG. 7. This shows the detail of the lower portion of the sealing element 230. However, it will be appreciated that the description here also applies to the upper portion of this sealing element as well as the other sealing element 228. As shown in FIG. 7, in cross-section, the seal has a generally right angled isosceles triangle shape. In practice, it may have the more complex cross-section shown in FIGS. 4 to 6 in which there is an additional annular projection extending towards the second fluid duct 242.

(21) As shown in FIG. 7, the spring 22 generates an axial spring force 250 on the end plate 226. This engages with an inclined face 252 of the sealing element 230 inclined at an angle of approximately 45 with respect to the axis X of the glass tube 220. The plate 226 applies a component 254 of the spring force to a radial component 256 which forces the seal 230 against the glass tube 220 and an axial component 258 which presses the seal 230 against the second fluid device 242.

(22) As is apparent from FIG. 7, most of the perimeter of the sealing element 230 is constrained by surfaces so that there is very limited ability for the element 232 to undergo creep even at relatively high temperatures. There will inevitably be some unconstrained surfaces to allow for the clearance between the second fluid device 242 and the housing 200. Given the smallness of the surfaces where creep can occur, this does not unduly affect the lifetime of the seal.

EXAMPLE

(23) In the flow reactor the manifold 114 the end caps 104, 106 are typically operated between 40 C. and 250 C. giving a range of 290 C. The manifold which is typically glass has a lower coefficient of thermal expansion (410.sup.6/K) compared with the end cap which is typically stainless steel (1610.sup.6/K). The result is that the stainless steel expands and contracts to a greater extent than the glass over the 290 C. range. Given that the thickness of the glass manifold is 50 mm, then the difference in thermal expansion between the glass manifold and the stainless steel endcaps is:
50 mm(1610.sup.6/K410.sup.6/K)290K=0.17 mm

(24) In order to maintain a fluidic seal the expansion and contraction must be absorbed by the sealing assembly. This also takes up some of the tolerances in the assembly. For example, the manifold 114 typically has a thickness tolerance of +/0.2 mm which is determined by the manufacturing process. The sealing assembly also absorbs this tolerance along with fabrication tolerances in the stainless steel endcaps 104, 106.

(25) When the housing cap 204 is assembled with the housing base 202 the spring 222 is compressed so that the force in the spring is 100-1000 N. This is a typical force for the reactor of FIGS. 1 and 2 and would need to be scaled up for a larger seal.

(26) In this example the compression force on the spring 222 will be 400 N. The surface area of the sealing element that comes into contact with the fluid duct 240, 242 or glass pipe is around 40 mm.sup.2. This results in a surface pressure of 10 MPa (100 Bar). This pressure indicates the operating pressure of the sealing element, although a safety factor is normally used so the actual operating pressure may be 25-50 Bar.

(27) The 10 MPa stress that the sealing element experiences results in around 3% strain (based on a Young's Modulus of the material of 350 MPa). As a result the seal is compressed and the internal surface of the seal is pressed onto the outer surface of the glass tube 220. This results in a surface pressure on the glass tube which results in a seal between the ferrule and the glass tube.

(28) The angle on the ferrule can be adjusted to reduce or increase the surface pressure on the inside surface of the seal. It is typically set to around 45 which ensures that the surface pressure on the inside surface of the seal is approximately equal to the surface pressure on the face of the seal.

(29) The maximum sealing pressure of the sealing assembly is approximately equal to the surface pressure of the sealing element, which is directly related to the compression force in the spring. By pre-compressing the spring 222 it is possible to ensure that there is enough spare spring force available across the range of movement of the seal.

(30) For example the spring 222 may typically be compressed by 3 mm giving a spring force of 300 N. When the seal assembly is clamped between the fluid ducts 240, 242 it is compressed by a further 1 mm resulting in a force of 400 N. During normal operation the length of the sealing assembly may vary by +/0.5 mm as a result of thermal expansion/contraction and manufacturing tolerances. This results in a level of compression of 4 mm+/0.5 mm which equates in a spring force of 400 N+/50 N. This force range equates to a surface pressure of 100 Bar+/12.5 Bar which is arranged to exceed the operating pressure range of the seal (25-50 Bar).

(31) A second example of a seal assembly is shown in FIG. 8. This example has the glass tube 220, the spring 222, the sealing elements 228, 230 and the ducts 240, 242 are as previously described. The previously described housing 200 and end plates 224, 226 have been modified. In particular, there are no separate end plates. Instead, the housing 300 is a base 302 with a cap 306 press fitted into the base 302, the lip 308 on the base 302 engages in a groove 310, cap 306. Lip 308 is free to slide within the base 310 but, as before, the spring 222 can exert a biasing force on the sealing element 228 and 230.

(32) A third example is shown in FIG. 9. This modification is based on FIG. 8, but the same modification can also be applied to the first example of FIGS. 3 to 7. Thus, the elements 228 and 230 have a square cross-section. In this case, the force applied by the spring 122 will compress the sealing elements 228, 230. The deformation caused by this compression will set the sealing elements. This shape of seal is therefore more applicable to softer seal materials. However, the sealing element is still largely constrained around its perimeter.

(33) As a further alternative, each sealing member could be an O-ring, but this is harder to constrain in the same manner.

(34) In a further modification, the spring 222 may be replaced by a form of biasing means such as disc springs, it may alternatively be a number of elements spaced around the tube 220, such as resilient rods or smaller springs.