The invention relates to a double-walled conductor system particularly suitable for transporting foodstuffs and aggressive substances such as strong acids and bases. The inner conductor transports the liquid for transporting, while the outer conductor serves to take up any liquid which may have leaked from the inner conductor and to detect that'leakage has taken place.

It is the object of the invention to provide such a double-walled conductor system which is reliably leak- proof, also at higher pressure and for a longer time, and which is simple to assemble.

This object is achieved with the conductor system as characterized in claim 1. The flange parts of adjacent conductor pieces can be mounted against each other or the flange part of a conductor section can be mounted to a pump, reservoir, valve or the like. After mounting of the flange part the outer conductor can be placed in sealing contact with the second sealing surface, so that a good seal of the outer conductor is achieved.

A very suitable embodiment of the invention is characterized in claim 2. The forces occurring in longitudinal direction of the inner conductor due to the pressure of the transported liquid are absorbed by the woven reinforcing sheath and transmitted to the coupling part on the opposite end. The inner conductor itself can hereby remain free of tensile stress.

The fixing means for the reinforcing sheath can be mounted in very simple and rapid manner by applying the step of claim 3.

Mutually connecting sections of the inner conductor can be connected to each other in reliably sealed manner by applying the step of claim 4. When the inner conductor

is of plastic the widened conductor parts can be directly clamped against each other. When for instance stainless steel is used for the inner conductor, a sealing spring can be arranged between the mutually facing flanges of the widened inner conductor parts.

The step of claim 5 is applied in accordance with a favourable further development. It has been found that PTFE has longer-term resistance to aggressive substances than for instance stainless steel, which after a period of time may begin to display some micro-corrosion of the surface, whereby deposition may occur more frequently.

The outer conductor can be of common steel, stainless steel or plastic.

The outer conductor can be mounted in simple manner by applying the step of claim 7. Mutual connection of the flange parts is arranged in simple manner as a closing operation of the screw cap, whereafter the outer conductor is mounted in the correct manner.

If the step of claim 8 is applied, heated thermal oil can for instance be transported through the outer conductor in order to heat liquid transported through the inner conductor. Heating of the transported liquid can also be achieved by arranging an electric heating line round the inner conductor. This electric heating line is arranged in well protected manner in the outer conductor. In addition to a plurality of conductor sections the conductor system according to the invention can also comprise cross pieces or T-pieces for forming of branches or connections of conductor parts. These cross pieces or T-pieces can be mounted on the conductor sections without special adaptation when the step of claim 10 is applied. A suitable further development is characterized in claim 11. The sliding piece compensates for expansions and contractions of the outer conductor but moreover makes it possible to axially shorten the outer conductor during assembly of the inner conductor and to extend the former to its full length again for mounting of the outer conductor.

The invention will be further elucidated in the following description with reference to the embodiments shown in the figures.

Figure 1 shows a part of a conductor system according to the invention.

Figure 2 shows a partial longitudinal section of a coupling of the conductor system of figure 1 as according to arrow II in figure 1.

Figure 3 shows a partial longitudinal section of a sliding piece of the conductor system of figure 1 as according to arrow III in figure 1.

Figure 4 shows a partially sectional T-piece with conductor sections connected thereto.

Figure 5 shows a partial section of another embodiment of a T-piece.

Figure 6 again shows another embodiment of a cross piece for the conductor system according to the invention.

Figure 7 shows a view corresponding with figure 2 of another embodiment.

The part of a conductor system 1 shown in figure l comprises conductor sections 2 which are mutually connected by couplings 3. Included in conductor sections 2 are sliding pieces 5 which will be described further. The embodiment of the coupling is shown in figure 2. It can be seen that an inner conductor 12 and an outer conductor 13 are joined collectively in coupling 3.

The core of coupling 3 is formed by the flange part 10 which has a first sealing surface 11 which is directed outward relative to the associated conductor section. This first sealing surface 11 co-acts with the inner conductor 12. This inner conductor 12 is inserted into flange part 10 through a central bore 9. The end of the inner conductor 12 placed through flange part 10 is widened to such a degree that a flange 20 lying transversely of the longitudinal direction is formed.

As shown in figure 2, this flange 20 is laid against the corresponding flange of an adjacent inner conductor

and fixedly clamped thereagainst by clamping the two flange parts 10 of the adjacent couplings against each other, in this case using a number of screw bolts 24. The inner conductor 12 can for instance be of stainless steel. However, it is preferably of polytetrafluoroethylene, whereby a longer life-span can be achieved. In the shown embodiment the inner conductor 12 is enclosed by a reinforcing sheath 16 of for instance stainless steel wire woven therearound. This sheath 16 is fixed onto a butt end 14 connected to flange part 10. This butt end 14 has a tubular end 17, a conical surface 18 connecting thereto and, in turn adjoining this latter, a screw-thread 15. A nut 21 can be screwed onto this screw-thread 15. This nut is provided with an interior conical surface 19 which can co-act with conical surface 18 of butt end 14 for fixedly clamping the end of the woven sheath 16 between these two surfaces 18, 19. Owing to this connection of woven sheath 16 to butt end 14, which is formed integrally with flange part 10, tensile forces from the one flange part 10 can be transferred to the flange part on the opposite end of the conductor section without the inner conductor 12 herein being exposed to a tensile strain.

Instead of fixing the reinforcing sheath using a clamping nut, it is also possible to fixedly shrink a clamping sleeve hydraulically round the butt end with the sheath arranged therearound. This embodiment is particularly recommended in the case of larger diameters of the inner conductor. The butt end is in this case not provided with a screw thread but with several ribs in order to enable a good engagement of the reinforcing sheath on the butt end.

In this embodiment of the invention the outer conductor 13 is a conductor which is constructed from commercially available plastic conductor elements. The tubular conductor element 27 is connected integrally via a welded socket 6 to a conductor element bearing a flange 26. By means of a screw cap 29 this flange 26 is fixedly

clamped with a head end surface against a second sealing surface 25 of flange part 10. A sealing ring 28 is arranged in this second sealing surface 25. The screw cap 29 engages on threading arranged on the outer periphery of flange part 10.

Connected to the outer conductor 13 close to the coupling 3 is a connection 23 through which for instance thermal oil can be circulated through the interspace between the interior of outer conductor 13 and inner conductor 12.

It is also noted that the first sealing surface 11 in flange part 10 is formed in a recess 22 which has a slightly lesser depth than the thickness of the flange of the widened end of inner conductor 12. When two corresponding flange parts are tensioned against each other in the manner shown using the bolts 24 while the two flanges 20 of the adjoining inner conductors 12 are pressed against each other, these flanges are thus pressed together slightly whereby a very good seal is obtained. The flange part 10 seals with its first sealing surface 11 on the outer surface of inner conductor 12 and the mutually facing inner surfaces of the adjacent inner conductors seal against each other.

The inner conductors of conductor system 1 thus form a continuous conductor. Because the ends of the mutually facing inner conductors are widened, a smooth widening is formed at the position of the "weld" whereby the growth of deposits is avoided.

If leakage should still occur in any way, the leaked substance enters the outer conductor 13, in which for instance sensors can be arranged for detecting the presence of this substance. With a connection such as for instance the connection 23 it can also be determined whether liquid which may have leaked out of the inner conductor has collected in the outer conductor. An indication of undesired leakage can also be obtained in this manner.

The conductor section 2 comprises at least one sliding piece 5 in the outer conductor 13. As figure 3 shows, this sliding piece can also be a commercially available conductor element which is incorporated by means of welded sockets 6 in connecting conductor elements in order to form the outer conductor 13.

The sliding piece comprises an inner tube 30 and an outer tube 31 slidable thereover. Outer tube 31 is provided on its end with a chamber 32 in which is arranged a sealing element 33.

Sliding pieces 5 serve on the one hand to absorb expansions and contractions resulting for instance from temperature changes in the conductor. Although this is not shown, the inner conductor 12 is supported at regular intervals in the outer conductor by spacers. If the inner conductor expands, for example through an increase in temperature, it will begin to sag slightly between the spacers, whereby the inner conductor takes on a wave-like form. No further provisions need therefore be made in the inner conductor to absorb expansions and contractions. In addition to absorbing expansions and contractions, sliding pieces 5 also have a function during mounting of a conductor section 2. During mounting the sliding pieces are pushed in, as seen in figure 2, the flange 26 of the outer conductor is shifted to the left, whereby the end part 17 of the butt end 14 of the flange part 10 can be reached and the outer sheath 16 can be mounted to the correct length. After widening of the end of inner conductor 12 the coupling can be mounted by arranging and fixing the bolts 24. Sliding piece 5 is then extended again until flange 26 lies against the second sealing surface 25, whereafter the former is secured in place with screw cap 29.

Also shown in figure 3 is the above described construction of the outer conductor 13 from commercially available conductor elements. On the right-hand end a part provided with a flange 26 is present, which part is connected via a welded socket 6 to sliding piece 5. The

sliding piece 5 is in turn connected via a welded socket 6 to a further conductor part 34. The welded sockets 6 are commercially available welded sockets, using which a reliable weld can be formed with controlled electrical heating elements.

The conductor system according to the invention can also comprise branches and cross connections. Figure 4 shows a cross piece 40 with which a T-connection or a cross connection can be formed. The cross piece 40 is provided with a central bore in which is received a core piece 45, for example pressed therein. This core piece 45 is provided with bores 46 which form the connecting channels.

The conductor sections which form the continuous connection are provided on their end with flange parts 41 differing slightly from the flange parts 10 described with reference to figure 2. The flange part 41 comprises a second butt end 42 which protrudes to the side remote from the conductor section. The inner conductor 43 is extended through this butt end and widened at its end, as is designated at 44. The head end of butt end 42 forms the first sealing surface of the flange part 41.

The core piece 45 is manufactured in this embodiment from the same material as the inner conductor 43, i.e. polytetrafluoroethylene. The butt end 42 is screwed into cross piece 40, wherein the widened end 44 of conductor 43 is pressed against core piece 45. A closed connection is hereby created. The coupling piece and/or the butt end 42 can optionally be heated slightly so that the widened end 44 is fixedly welded to the core piece 45 to a greater or lesser extent.

The branching conductor section 48 has a flange part 10 identical to that described with reference to figure 2. The flange part 10 is tightened against the end surface of cross piece 40 using bolts 47, so that the flange 20 formed by the widened end of the inner conductor is pressed against the head end of core piece 45. In this embodiment a closing plate 49 is arranged on

the opposite side. Another conductor section can of course also be connected instead so that a cross connection is formed.

Figure 5 shows another accessory with which a T- connection can be formed. In this embodiment this T-piece 50 is made of plastic and provided with internal bores in which are received insert conductors 51 and 52 of for instance polytetrafluoroethylene. Firstly the insert conductor 52 provided with a transverse bore is pushed into the T-piece 50, whereafter the insert conductor 51 is arranged. The insert conductors 51 and 52 remain protruding slightly out of the T-piece 50, so that after fitting of the conductor sections they come under pressure. A good seal can hereby already be obtained between insert conductors 51 and 52. Insert conductor 51 can optionally be welded to insert conductor 52 by supplying heat or by ultrasonic means.

The head end of insert conductor 51 comes into contact with the ends, widened into a flange, of the inner conductor of the connecting conductor sections. As figure 5 shows, these conductor sections have a flange part 10 which corresponds with the flange part described with reference to figure 2.

Figure 6 shows schematically yet another coupling piece for forming a cross connection. The cross piece 57 is manufactured from a block of suitable material, for instance of polytetrafluoroethylene. Formed in this block 57 are mutually connected bores 58, 59 lying transversely of each other which form the connections for the inner conductors. Bores 60, 61 are likewise arranged to allow passage of bolts with which the flange parts of the conductor sections for connecting are pulled toward each other and against cross piece 57. The flanges formed by the widened ends of the inner conductors herein lie directly against the cross piece 57, and thus form a sealed connection.

Instead of from polytetrafluoroethylene the cross- piece 57 can of course also be manufactured from another

material, for example stainless steel. It is recommended to manufacture the block 57 from the same material as that from which the inner conductors of the conductor sections for connection are manufactured. The invention is not limited to a conductor system with couplings which are mutually connected by bolts. The couplings can be mutually connected by any suitable connecting technique, such as for instance glueing or welding. In this respect figure 7 shows a view corresponding with figure 2 of a glued connection. The coupling 63 herein connects two conductor sections 64, 65. The flange parts 66, 67 are herein for example of a suitable plastic which can be glued well and are permanently joined to each other by glue 68. In this embodiment the inner conductors are also of a material which can be glued well and the flanges 69, 70 formed by the widened ends of the inner conductors for mutual connection are likewise sealingly joined to each other by the glue connection 68. Although the connection of the outer conductors to flange parts 66, 67 is shown here as screw connections, it will be apparent that these connections can for instance also be glued or welded.

Particularly in the case of smaller diameters of the inner conductor and a relatively low pressure up to a few tens of bar, plastic can be used in suitable manner for the couplings and T-pieces or cross pieces. With larger diameters and/or higher pressures the fittings are preferably manufactured from metal, wherein stainless steel is again recommended.