GB2040388A - Improvements in and relating to tubing and tube connectors - Google Patents

Abstract

Tubing for high pressure applications comprises an inner plastics tube (10) which is a sliding fit within an outer sheath (12). The latter is impervious to the fluids contained within the tube (10). The outer sheath may be metal, plastics or rubber and the inner tube may be p.t.f.e. A connector for such tubing comprises a metal sleeve (22) which radially locates a cylindrical metal cup-shaped member (26) the base of which constitutes a thrust plate which is apertured at 30 to receive the sheath (12) and at 28 to receive the tube (10). The bore (28) is formed with an annular barb (38) which bites into the tube (10) to prevent withdrawal. A block of deformable plastics material p.t.f.e. (32) is contained within the member (26) and receives the tube (10) within a bore thereof. A closure member (16) is threaded into the sleeve (22) to tension bevelled spring steel washers (24) against the base of member (26). The inner end face (36) of the block (32) is pressed against a flat seating within a sleeve (22) or the end face of a similar block (36') to complete the seal and allow the first pipe (10, 12) to be connected e.g. to a second pipe (12', 10'). <IMAGE>

Description

SPECIFICATION Improvements in and relating to tubing and tube connectors This invention concerns tubing and tube connectors.

Plastics materials in general, and fluoropolymeric plastics in particular (polytetrafluoroethylene PTFE and ethylenetetrafluoroethylene ETFE and the like), have achieved almost universal use in laboratories and instrumentation for interconnecting apparatus and components in analytical equipment and the like. Materials such as PTFE are exceptionally inert chemically and the ability to cut tubing to length and to bend it easily is of considerable advantage.

Unfortunately such plastics materials and particularly PTFE, exhibit a degree of porosity to gases and vapours. This porosity prevents them from being used in certain applications despite their otherwise superior chemical properties. These gaseous exchanges can interfere with the analyses being made, either by altering the properties of the substances being analysed or otherwise adversely affecting the tests. Alternatively, such exchange may create a risk of harmful materials escaping by diffusion through the tube wall thus contaminating the environment.

In addition to these limitations, the use of these materials for plastics tubing carrying fluids under pressure has hitherto been restricted to relatively low pressure applications since the tubing and connectors available hitherto have not been able to withstand the relatively high internal pressures, i.e.

in excess of one thousand pounds per square inch.

Beyond this pressure barrierthe tube wall has been found to weaken, an aneurysm has developed in the tube and if pressure has not been immediately reduced, the tube has ruptured.

The present invention seeks to provide an improved form of tubing.

The invention also provides an improved tubing connector for use with the improved tubing.

Both the improved tubing and the improved connector seek to isolate a flexible internal plastics tubing from the environment and also prevent it from rupturing under high internal pressures.

According to one aspect of the present invention tubing for containing fluids in excess of one thousand pounds per square inch comprises an inner plastics tube and an outer strengthening sheath within which the inner tube is a sliding fit.

The outer strengthening sheath is formed from metal or an impervious plastics or rubber material or a composite thereof.

According to another aspect of the present invention an improved connector for use with tubing formed from an inner plastics tube and an outer strengthening sheath within which the innertubeis a sliding fit, comprises:~ - an apertured thrust plate to which an end of the sheath can be secured, - a block of resiliently deformable plastics material having parallel end faces one of which abuts the thrust plate, and having an axial bore which extends between the opposite parallel end faces and with which the inner tube communicates, - a rigid containing surface around the block which restricts deformation of the block in a radially outward direction when the block is subjected to compressive forces between opposed parallel end faces, - a sleeve into which the sheathed tube, thrust plate and block of plastics material are removably secured, and - spring means acting on the outermost end face of the thrust plate to urge the remote parallel end face of the block of plastics material into sealing engagement with a flat surface of a cooperating member.

The cooperating member is conveniently apertured in alignment with the axial bore in the first mentioned plastics block and may comprise a flat seating within the sleeve or an opposed flat end face of another similar plastics block similarly located within the sleeve from the opposite end thereof and sealingly engaged on a second length of inner plastics tubing, to allow the first mentioned inner plastics tube to be connected to the second mentioned inner plastics tube without any break in the encircling protection so as to prevent rupturing of the tube due to high internal pressures.

In one embodiment the inner plastics tube extends through the axial bore through the block and is sealingly secured therein.

In another embodiment the tube is cut off flush with the end face of the thrust plate which abuts the block and the diameter of the bore through the block is selected so as to correspond to the inner diameter of the inner plastics tube.

In a third embodiment the tube is flanged and sandwiched between the inner end face of the thrust plate and the outer end face of the block of plastics material.

In any one of the three mentioned embodiments a barb-shaped projection typically of annular configuration may be provided on the inside surface of the aperture in the thrust plate, the direction of the barb being such as to bite into the wall of the inner tube when the latter is pulled in a direction so as to pull the tubing from out of the thrust plate away from the block of plastics material.

In the third mentioned embodiment, an axial annular protrusion is pivotally formed around the exit of the bore through the thrust plate so that the flange of the tube sandwiched between the plate and the block is nipped by the annular ridge formed by the axial annular protrusion and is thereby prevented from flowing in a radially inward and axially outward direction when the inner tubing is subjected to high internal fluid pressures.

The plastics tube may be secured within the block of plastics material by means of an adhesive instead of or in addition to the use of the barb-shaped projection or annular protrusion previously mentioned.

Preferably the thrust plate formed at the base of the cup-shaped member and the cylindrical section of the cup-shaped member extending from the base thereof constitutes the rigid bounding surface which surrounds the block of plastics material.

Conveniently a threaded member is provided which is adapted to be removably secured to the end of the sleeve through which the sheathed tube and other components are introduced into the sleeve, the threaded member including an aperture through which the sheathed tube can pass and the threaded member constituting a surface against which the spring means acts to provide the axial thrust required on the outermost end face of the thrust plate.

Conveniently the threaded member is in the form of an externally threaded cylindrical plug which is conveniently formed with at least one recess in its outermost face to allow a tool to be fitted thereto to screw the member into the sleeve.

By making the threaded member of metal the spring means will be located between two plain metal surfaces, one being the inner end face of the threaded member and the other the outwardly directed end face of the thrust plate.

Conveniently the spring means comprises at least one and preferably three sets of spring steel washers sometimes known as bevelled washers and sold under the Trade Name Belville washers.

Preferably the rigid bounding surface within which the block of plastics material is contained is itself accurately aligned within the sleeve to assist in the alignment of the inner plastics tube with the aperture in the opposed end flat face or flat seating against which the block of plastics material abuts when the connector is assembled.

According to a preferred feature of the invention, where the thrust plate and rigid bounding surface comprise the base and cylindrical section of a cupshaped member, the open circular end of the cylindrical section of the cup into which the block is fitted, is chamfered and the block of plastics material is cylindrical and of a diameter such that it is an interference fit within the cup and protrudes axially therebeyond, the axially protruding portion being of increased diameter relative to the remainder of the block so as to provide an annular flange of deformable plastics material which is firmly embedded againstthe circular chamfered edge of the cylindrical section of the cup-shaped member.

Where the opposed flat end face against which the inner end face of the first mentioned block abuts is a similar inner end face of a similar plastics block mounted in a similar manner within the sleeve, the second mentioned block also including an annular flange of deformable plastics material embedded on the chamfered annular rim of the other cup-shaped member, the axial thrust applied to the rear of the two cup-shaped members by the two opposed spring assemblies will cause the two annular flanges of deformable plastics material to become nipped between the two chambered annular rims of the two cup-shaped members within which the blocks of plastics material are contained and a good peripheral seal will thereby be formed by the nip so created.

In another embodiment of the invention the inner end face of the plastics block is formed with a tapering recess, the angle of the taper being such that the mouth of the recess in the said inner end face is of larger diameter than the bore through the block through which the plastics tube is pushed and the flat seating against which the block of plastics mater ial would otherwise be pressed is replaced by a complementary conical surface which extends into the protruding plastics tube so as to cause the latter to be flared radially outwardly until it is trapped between the two complementary conical surfaces thereby to form a good seal at the junction.

Preferably the plastics material is polytetraf luroethylene (PTFE).

Preferably the outer strengthening sheath is of metal although a hardened plastics material may alternatively be used.

The sleeve may be formed from metal or from a hardened plastics material.

As a connector, the sleeve is fitted to two tube ends which are to be joined together.

Where a tube is to be connected to a component, the component is adapted to provide the flat seating (or conical outstanding surface) against which the plastics block is sealingly urged and the sleeve is conveniently formed integrally with the component or may be a separate attachment secured thereto for example by means of a screw-threaded engagement.

The invention will now be described by way of example with reference to the accompanying drawings.

Fig. 1 is a cross-section through a pipe connector embodying the invention in which the component parts of the fitting are shown in cross-section in the left-hand half and are not sectioned in the right-hand half of the figure, Fig. 2 is an end view of the fitting shown in Fig. 1, and Fig. 3 is a cross-section of the fitting shown in Fig.

1 on the line Ill-Ill.

A fitting is shown in the drawings by which two pipes can be connected together. Each pipe is formed from two parts an inner plastics tube 10 and an outer metal sheath 12. The fitting is symmetrical about the centre line denoted by the numerals Ill-Ill and those component parts of the fitting and the piping on the right-hand half of the view are denoted by the same reference numerals as used to denote similar parts on the left-hand side but with the addition of a suffix.

The outer sheath extends through a bore 14 through a circular externally threaded bung 16 having tooled recesses 18 and 20 in its outer face to allow a 2-pronged tool to be inserted and the bung rotated for screwing in or screwing out of the fitting.

The main part of the fitting comprises a generally cylindrical sleeve 22 which has a reduced diameter central region and is formed with a screw-thread profile at its two opposite ends on the inside surface thereof.

Referring particularly to the left-hand end of the fitting shown in Fig. 1, the sheath 12 and innertube 10 extend beyond the inner end of the bung 16 and extend through a stack of three Belville or bevelled washers 24 which constitute a resilient compression spring.

The washers 24 are sandwiched between the inner end face of the bung 16 and an outer end face of a metal cup 26 which has a through-bore 28 and an annular recess 30 surrounding the exit of the bore 28 in the end face of the cup, the recess 30 receiving the inner end of the sheath 12. The shoulder formed by the recess 30 constitutes an abutment against which the end of the sheath abuts.

The cup 26 is generally cylindrical and has fitted therein a cylindrical block of PTFE designated by reference numeral 32. The block is formed with a throughbore 34 which aligns with the throughbore 28 in the base of the cup 26 and the plastics inner tube 10 extends completely through the aligned bores 28 and 34. The end of the inner tube 10 is cut off in alignment with the innermost flat end 36 of the block 32.

In the bore 28 is an annular barblike protrusion 38 which is directed into the bore in such a way that the plastics tube 10 can be pushed from the left to the rightthroughthe base of the cup 26 but immediately the tube is pulled in the opposite direction (i.e. from right to left) the barblike projection 38 bites into the wall of the tube and prevents the tube from being pulled backwards.

Although the barb 38 has been described as a single annular projection it will be appreciated that the invention is not limited to a single annular barblike protrusion but more than one such annular barb-like protrusion may be employed or a plurality of barblike protruding teeth may be provided within the bore 28 not necessarily annularly arranged but located so as to bite into the wall of the tube in the same manner as described for the annular barblike protrusion 38.

The protruding ends of the blocks 36 and 36' are formed with annular flanges of greater diameter than the remainder of the blocks and designated by reference numerals 39 and 39' respectively. The annular flanges 39 and 39' are trapped between the chamfered circular rims of the two cup-shaped members 26 and 26' and the axial thrust exerted on the rear of the two cup-shaped members 26 and 26' by the springs 24 and 24' serves to form an annular nip around the two flanges 39 and 39' to form a good seal therebetween.

The fitting is assembled by first of all threading the bung 16 into the outer sheath 12 with the inner tube 10 extending therethrough. The Belville washers 24 are then threaded onto the sheath 12. The sheath is of a length such that the inner plastics tube 10 protrudes by a few inches beyond the end of the sheath and the protruding plastics end is tapered for example by shaving to allow it to be introduced into the bore 28 in a cup 26 containing a PTFE block 32. The plastics tube is pulled through the aligned bores in the cup and block until the end of the sheath 12 is received into the recess 30 and is held captive therein. The end of the plastics tube 10 protruding from the end face 36 is then trimmed so that the tube end is flush with the end face 36 of the block 32. The tube 12' is similarly secured in the block contained within the cup-shaped member 26'.

Although not shown, an adhesive or solder or similar means may be used to secure the sheath 12 into the annular recess 30 in the end face of the cup 26.

In a similar way the shaved ortapered end of the tube 10 may be covered with an adhesive before it is introduced into the bore through the block 32 so that the tube and block are securely bonded together when the adhesive sets hard.

The cup 26 is now introduced into an end of a cylindrical sleeve 22 and the bung 16 is engaged with the screw-thread on the inside surface of the sleeve and rotated so as to be screwed into the fitting thereby compressing the Belville washers 24 and exerting an axial thrust on the rear of the cup 26.

A similar assembly is inserted into the opposite end of the fitting and the bung 16' similarly rotated and screwed up until the pressure exerted between the two abutting faces 36 and 36' is sufficient to seal the joint between the two tubes 10 and 10' to withstand the pressure of the fluid within the tubes.

It will be seen that the invention allows two plastics tubes to be joined together using at least in part metal fittings thereby allowing considerable strength to be provided at the fitting and to allow considerable axial thrust to be exerted across the joint and across the sealing interface so that there is little chance of leakage occurring at the fitting.

The invention also allows a variation in the thrust exerted across the sealing interface (between the two blocks 32 and 32') so that only just the required thrust is exerted on the plastics blocks 32 and 32' so as to contain the pressures to which the fitting is to be subjected.

Fig.2 2is an end view of the fitting when assembled and shows the bung 16 and the two tooled recesses 18 and 20 with the metal sheath 12 and inner tube 10 protruded through the centre of the bung. The bung is shown screwed into the end of the fitting 22 which in this case is shown to be of circular cross-section. It will be appreciated that the sleeve 22 need not be of circular external shape and square or hexagonal faces may be provided to advantage around the external surface at least over part of the length thereof to allow the latter to be gripped to assist in exerting torque on the bungs 16 and 16'.

Fig. 3 is a cross-section on the line Ill-Ill in Fig. 1 and shows the innermost end of the tube 10 cut flush with the end face 36 of the block 32 held captive within the cup 26.

According to a preferred feature of the invention a close slipping fit is provided between the outside surface of the cup 26 and the inner surface of the reduced diameter section of the sleeve 22 so as to align the cup 26 with the remaining parts of the connector such as an adjoining cup 26'. In this way good alignment of the fluid passages formed by the tubes 10 and 10', can be achieved.

It will be appreciated that the end face 36' of an opposite block 32' introduced from the right-hand end of the fitting 22 can be replaced by a fixed flat seating having an aperture therethrough communicating with the internal fluid ducts within a component such as a valve, pump, etc. The righthand end of the fitting as shown in Fig. 1 is then dispensed with and the fitting sleeve 22 may be formed integrally with the body of the component or may be a screw-on attachment surrounding the flat seating and central aperture to which the tube is to be connected.

The primary advantage of the invention will be lost if the flat seating surface of the alternative arrangement just described (but not shown) is not formed from a plastics material such as polytetrafluoroethylene and in that event the outer sleeve 22 may be formed from PTFE itself or may be formed from metal as previously described and bonded to a PTFE housing of the component (not shown). Alternatively a PTFE insert may be located in a metal fitting to provide a PTFE passage and flat end face seating to replace the surface 36' provided by the plastics block 32' of the embodiment actually shown in Fig. 1.

The invention allows the advantages of plastics tubing and plastics connectors to be obtained in systems requiring considerably higher pressures to be contained within the tubing and connectors than has hitherto been the case with standard plastics components. This primarily arises from the fact that the plastics tubing 10 and 10' is wholly contained within a metal sheathing or a passage in a member of plastics material which itself is bounded by metal at all points along the length of the plastics tubing.

Since most plastics materials are porous to certain gases and vapours, the presence of the metal sheathing will preventthe ingress of oxygen, nitrogen, carbon dioxide, etc. from the surrounding air and therefore will allow a liquid to be conveyed and stored within the tubing without the risk of contamination due to the ingress of such gases as otherwise would be the case. This is particularly important when the overall system within which the tubing is used is required to measure inter alia the gaseous content of the liquid for example oxygen content of fluids.

It is to be understood that the invention is not limited to the particular method of securing the plastics tube 10 to the cup 26 and block 32 and any convenient method may be used such as described in the foregoing description without reference to the drawing.

Claims (32)

1. Tubing for carrying fluids under pressure comprising an inner plastics tube and an outer strengthening sheath within which the inner tube is a sliding fit.

2. Tubing as claimed in claim 1 in which the outer strengthening sheath is formed from metal.

3. Tubing as claimed in claim 1 in which the outer strengthening sheath is formed from plastics material which is impervious to the fluids contained in the plastics tube.

4. Tubing as claimed in claim 1 in which the outer strengthening sheath is formed from rubber which is impervious to the fluid which is to pass through the plastics tube.

5. A connector for connecting to tubing as claimed in claim 1 comprising: - an apertured thrust plate to which an end of the sheath can be secured, - a block of resiliently deformable plastics material having parallel end faces one of which abuts the thrust plate, and having an axial bore which extends between the opposite parallel end faces and with which the inner tube communicates, - a rigid containing surface around the block which restricts deformation of the block in a radially outward direction when the block is subjected to compressive forces between opposed parallel end faces, - a sleeve into which the sheathed tube, thrust plate and block of plastics material are removably secured, and - spring means acting on the outermost end face of the thrust plate to urge the remote parallel end face of the block of plastics material into sealing engagement with a flat surface of a cooperating member.

6. Atubing connector as claimed in claim Sin which the cooperating member is apertured in alignment with the axial bore in the first mentioned plastics block.

7. A tubing connector as claimed in claim 6 in which the cooperating member is a flat seating within a sleeve.

8. Atubing connector as claimed in claim 6 in which the cooperating member comprises the flat end face of a second plastics block also located within the sleeve but from the opposite end thereof and sealingly engaged to a second length of inner plastics tubing, the connector serving to join the first mentioned inner plastics tube to the second mentioned inner plastics tube.

9. A tubing connector as claimed in any of claims 5 to 8 in which the inner plastics tube extends through the axial bore in the block and is sealingly secured therein.

10. Atubing connector as claimed in any of claims 5 to 8 in which the first mentioned inner tube is cut off flush with the end face of the thrust plate which abuts the block and the diameter of the bore through the block is selected so as to correspond to the inner diameter of the severed plastics tube.

11. Atubing connector as claimed in any of claims 5 to 8 in which the protruding end of the plastics tube is flanged and the latter is sandwiched bet ween the inner end face of the thrust plate and the outer end face of the block of plastics material.

12. Atubing connector as claimed in any of claims 5 to 11 in which a barb-shaped projection is formed on the inside surface of the aperture in the thrust plate, the direction of the barb being such as to bite into the wall of the inner tube when the latter is pulled in the direction so as to pull the tubing from out of the thrust plate away from the block of plastics material.

13. Atubing connector as claimed in claim 12 in which the barb-shaped projection is of annular configuration.

14. Atubing connector as claimed in claim 11 in which an axial annular protrusion is formed around the exit of the bore through the thrust plate so that the flange of the tube sandwiched between the plate and the block is nipped by the annular protrusion and is thereby prevented from flowing in a radially inward and axially outward direction when the inner tubing is subjected to high internal fluid pressures.

15. A tubing connector as claimed in any of claims 5 t Z 14 in which the inner plastics tube is secured within the block of plastics material at least in part by means of an adhesive.

16. A tubing connector as claimed in any of claims 5 to 15 in which the thrust plate comprises the base of a cup-shaped member and the cylindrical section of the cup-shaped member constitutes the rigid containing surface surrounding the block of plastics material.

17. Atubing connector as claimed in any of claims 5 to 16 further comprising a threaded member which is adapted to be removably secured to the end of the sleeve through which the sheathed tube and other components are introduced thereinto, the threaded member including an aperture through which the sheathed tube can pass and constituting a surface against which the spring means acts to provide the axial thrust required on the outermost end face of the thrust plate.

18. Atubing connector as claimed in claim 17 in which the threaded member is in the form of an externally threaded cylindrical plug formed on its outermost face with tool-receiving apertures to allow a tool to be fitted thereto to screw the member into the sleeve.

19. Atubing connector as claimed in claim 17 or 18 in which the threaded member is of metal so that the spring means is located between two plain metal surfaces, one being the inner end face of the threaded member and the other the outwardly directed end face of the thrust plate.

20. Atubing connector as claimed in any of claims 5 to 19 in which the spring means comprises at least one spring steel washer.

21. Atubing connector as claimed in claim 20 in which the spring means comprises a set of three spring steel washers.

22. Atubing connector as claimed in any of claims 6 to 21 in which the rigid containing surface is accurately aligned within the sleeve to assist in the alignment of the inner plastics tube with the aperture in the cooperating member with which the block of plastics material abuts when the connector is assembled.

23. Atubing connector as claimed in claim 22 wherein the thrust plate and rigid containing surface comprises the base and cylindrical section of a cupshaped member and the open circular end of the cylindrical section of the cup into which the block is fitted is chamfered and the block of plastics material is cylindrical and of a diameter such that it is an interference fit within the cup and protrudes axially therebeyond, the axially protruding portion being of increased diameter relative to the remainder of the block so as to provide an annularflange of deformable plastics material which is firmly embedded against the circular chamfered edge of the cylindrical section of the cup-shaped member.

24. Atubing connector as claimed in claim 23 wherein the opposed flat end face against which the inner end face of the first mentioned block abuts is a similar end face of a similar plastics block mounted in a similar manner within the sleeve, and wherein the second mentioned block also includes an annu larflange of deformable plastics material embedded on the chambered annular rim of another cupshaped member, so that the axial thrust applied to the rear of the two cup-shaped members by the two opposed spring assemblies within the sleeve will cause the two annular flanges of deformable plastics material to become nipped between the two chamfered annular rims of the two cup-shaped members within which the blocks of plastics material are contained and a good peripheral seal will thereby be formed by the nip so created.

25. Atubing connector as claimed in claim 6 in which the inner end face of the plastics block is formed with a tapering recess, the angle of the taper being such that the mouth of the recess in the said inner end face is of larger diameter than the bore through the block through which the plastics tube is pushed and the flat surface of the said cooperating member is replaced by a complementary conical surface which extends into the protruding plastics tube so as to cause the latter to be flared radially outwardly until it is trapped between the two complementary conical surfaces thereby to form a good seal therebetween.

26. Tubing and tubing connectors therefor as claimed in any of the preceding claims in which the plastics material is polytetrafluroethylene (PTFE).

27. Atubing connector as claimed in any of claims 5 to 26 in which the sleeve is formed from metal or from hardened plastics material.

28. Atubing connector as claimed in any of claims 5 to 7 or 9 to 23 or 25 to 27 inclusive when forming part of a component to which the improved tubing is to be secured.

29. A connector as claimed in claim 28 in which the sleeve is formed integrally with the remainder of the component.

30. A connector as claimed in claim 28 in which the sleeve is secured to the component by means of a screw-threaded engagement.

31. Tubing as claimed in claim 1 constructed and arranged substantially as herein described with reference to Fig. 1 the drawings.

32. Atubing connector constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in Figs. 1 to 3 of the drawings.