EP0706623A1

EP0706623A1 - Seat for the rotating shaft of a valve

Info

Publication number: EP0706623A1
Application number: EP94922048A
Authority: EP
Inventors: Antonius Adrianus Maria Voermans
Original assignee: Keystone International Holdings Corp
Current assignee: Keystone International Holdings Corp
Priority date: 1993-07-02
Filing date: 1994-06-30
Publication date: 1996-04-17
Also published as: WO1995001526A1; NL9301162A; AU7252694A

Abstract

The invention relates to a valve for a pipe or reservoir, comprising a housing, a shut-off element, a rotatable operating shaft which runs through the housing, and a primary seal on the shaft. Seen from the shut-off element a secondary seal is placed beyond the primary seal about the shaft. The secondary seal comprises a flexible bellows seal and a magnetic fluid seal ahead of and beyond which a fireproof shut-off ring is arranged about the shaft. Leakage from the pipe is detected with the help of a monitoring system. By means of a monitoring system it is checked whether or not leakage to the surroundings is taking place, whether maintenance should be carried out and whether the seal and/or portions thereof are intact.

Description

Seal For The Rotating Shaft Of A Valve

The invention relates to a valve for reservoirs and pipes, comprising a housing, a shut-off element, a rotatable operating shaft which runs through the housing, and a primary seal on the shaft. In pipe systems and reservoirs for fluids, gasses or vapors frequent use is made of valves for regulating the system and the reservoir. These valves are, for example, butterfly valves, plug valves and ball valves. For opening and closing, the operating shaft which extends outwards through the housing has to be rotated by hand or otherwise over an angle of 90° . A rotation of 180° is also possible, however. In order to prevent leaking of fluid a primary seal is arranged on the shaft.

A disadvantage of this known valve is that when in use, sooner or later the primary seal can start leaking. In pipe systems and reservoirs for dangerous substances this is exceedingly undesirable.

It is therefore an object of the invention to provide a valve having a seal on its shaft such that leakage along the shaft is reduced to a minimum.

In order to attain this object the valve according to the invention comprises in the first of its coordinate embodiments the measure that the valve comprises a secondary seal, which, as seen from the shut-off element, is placed beyond the primary seal about the shaft and comprises a bellows substantially manufactured from a flexible material, one end of the bellows being attached to the shaft and the other end to the housing, the bellows permitting the shaft to rotate along a part of a revolution, and with that twists, and a coiled spring being arranged on the side of the bellows which is turned away from the space which connects to the primary seal, which coiled spring supports the bellows, which coiled spring is manufactured from a substantially circular thread, and which is at least as long as the twisting portion of the bellows, and which coiled spring is attached with one end of the shaft and with the other end to the housing in order to obtain a torsion which substantially corresponds to that of the bellows.

By this it is achieved that the fluid which has leaked along the primary seal will be stemmed by the secondary seal. Because the bellows is attached with one end to the operating shaft and with the other end to the housing, a rotation of the operating shaft will merely result in a torsion of the flexible material of the bellows. Thus there is no sliding along the shaft or the housing, as with a conventional seal such as an O-ring, so that in this way no wear and therefore leakage can occur again. In the case of prolonged leakage the pressure on the bellows can become great. For that reason a coiled spring is arranged on the side of the bellows on which there is no pressure, which coiled spring supports the bellows. This coiled spring is manufactured from substantially round wire, so that in the case of high pressure of the leaked fluid the coiled spring will not cut into the flexible material. Because of its shape the coiled spring is automatically so rigid, that it does not have to be supported against the shaft or the housing. Because the coiled spring, just as the housing, is attached with one end to the shaft and with the other end to the bellows, and is at least equally long as the twisting portion of the bellows, at most only some displacement will take place between the bellows and the coiled spring when the shaft is rotated. As far as the secondary seal is concerned the required moment for rotating the operating shaft is thus kept as low as possible and is in effect limited to the moment that is required for twisting the bellows and the spring.

According to the second coordinate embodiment the valve according to the invention comprises the measure, that the valve comprises a secondary seal, which, as seen from the shut-off element, is placed beyond the primary seal about the shaft and comprises a bellows substantially manufactured from a flexible material, one end of the bellows being attached to the shaft and the other end to the housing, the bellows permitting the shaft to rotate along a part of a revolution, and with that twists, the flexible material of the bellows incorporating a coiled spring, supporting the bellows, the windings of which rest free from one another, and which is equally long as the twisting portion of the bellows.

In comparison with the first embodiment the coiled spring is incorporated in the flexible material of the bellows. To ensure that the bellows forms a unit, the windings of the coiled spring rest separate from one another. The operation of this embodiment of the secondary seal is the same as that of the above embodiment. According to the third coordinate embodiment the valve according to the invention comprises the measure, that the valve comprises a secondary seal, which, as seen from the shut-off element, is placed beyond the primary seal about the shaft and comprises a bellows substantially manufactured from a flexible material, one end of the bellows being attached to the shaft and the other end to the housing, the bellows permitting the shaft to rotate along a part of a revolution, and with that twists, and a synthetic having a very low friction coefficient being arranged on the bellows on the side of the bellows which is turned away from the space that connects to the primary seal, allowing support of the bellows against either the shaft, or the housing.

Instead of the coiled spring according to the first embodiment, in this embodiment the synthetic with a low friction coefficient is arranged which will indeed be supported against the shaft or the housing when the leaked fluid applies pressure to the bellows. The surface of the bellows is herewith equally loaded.

In this last embodiment it is advantageous to apply a lubricating fluid between the synthetic with a low friction coefficient and the flexible bellows. By doing this the required moment for rotating the operating shaft is kept as low as possible. In the first embodiment it is advantageous that the windings of the coiled spring rest against one another. Then, in the case of high pressures, the flexible bellows is not pressed between the windings.

In an advantageous manner the bellows has its released state between the opened and closed position of the shut-off element, preferably halfway through the total angle of rotation of the operating shaft. In this way only in the extreme positions of the shut-off element does the required moment for the twisting of the bellows reach its maximum value, which is lower than when the released state of the bellows is at a different angle of rotation of the operating shaft.

For many applications the total angle of rotation of the operating shaft is approximately 90° .

In the first embodiment the coiled spring advantageously has at least approximately 10-12 windings along the twisting portion of the bellows, at a total angle of rotation of the operating shaft of approximately 90° and the released state of the bellows halfway through the total angle of rotation. Under pressure of the leaked fluid the bellows now rests against so many windings that when the operating shaft rotates each winding shifts only a little in relation to the adjacent ones. The flexible material of the bellows can accommodate this slight shifting in the area between the adjoining windings, as a result of which the bellows does not have to shift over a portion of the windings. The required moment for rotating the operating shaft is thus minimized and limited to the torsion of the bellows and the spring itself. Neither will any wear of the bellows occur. The bellows is advantageously circularly cylindrical so that the load on it is symmetrical.

The bellows is substantially manufactured from rubber, from a synthetic, preferably a fluor polymer, or from a laminate of synthetics and/or rubbers. The material depends on the fluid which is sealed. In an advantageous way the end of the bellows which is to be attached to the shaft is of metal, to which the flexible part of the bellows is attached, and the metal end and the shaft being statically sealed in relation to each other, for example with the help of 0-rings.

In this way the bellows can easily be attached to the 30 shaft. Advantageously, the other end of the bellows is also made of metal. In this way the bellows can easily be attached to the housing. The metal end is advantageously attached to either the shaft or the housing by means of a pin. Because of this the bellows is easily detachable.

The flexible end of the bellows is advantageously attached to either the shaft or the housing by clamping. In this way a simple, leakproof retaining of the flexible end of the bellows is obtained. It is then of advantage that the flexible end of the bellows is provided with a metal ring. Then the end cannot be pulled out of the retaining.

If the bellows is made substantially of rubber, the flexible end of the bellows can also advantageously be attached to either the housing or to the shaft by vulcanizing. Consequently, a hermetically closed, static seal is formed. In the case of such an attachment free of pressure the chance of crack formation in the rubber is reduced.

The secondary seal also advantageously comprises a magnetic fluid seal, which, as seen from the shut-off element, is arranged beyond the bellows about the shaft. The flexible bellows will indeed stem liquids but will always be slightly permeable for vapors or gases. In order to prevent vapors or gases from leaking into the surroundings, the magnetic fluid seal is placed.

For shutting off the shaft of a valve the magnetic fluid seal comprises at least one magnet, magnetic liquid, a magnetic conducting component, and two pole pieces on both sides of the magnet, the magnet, the pole pieces, the magnetic liquid and the component forming a magnetic circuit.

Advantageously, the magnetic conducting component is the shaft itself, the shaft is round, and the magnet and the pole pieces are arranged annularly about the shaft, the pole pieces comprising various annular ridges, which are at a short distance from the shaft, and the magnetic fluid spanning the distance between the ridges and the shaft.

In this way a radial magnetic fluid seal is formed, in which the magnetic fluid between the shaft and the groove can always span a certain difference in pressure, proportional to the quantity of magnetizable particles in the fluid, as a result of which, depending on the number of ridges, the total pressure difference between the passed through gas or the passed-through vapor and the surroundings is spanned, so that no measurable quantity of passed through gas or vapor will make its way into the surroundings at all. The radial magnetic fluid seal has the advantages that no wear occurs, that no additional moment is needed when rotating the operating shaft, and that the seal can be small. To obtain an optimum seal the slot between the ridges and the shaft has to be small, so that the shaft has to be positioned accurately.

The magnetic fluid seal advantageously contains a magnetic fluid with a very high concentration of magnetizable particles, as a result of which the pressure difference which can be spanned per ridge increases. Highly magnetizable fluids display a very viscous behavior, so that the application can only be used with slow moving shafts, such as in a valve, and not with high-speed shafts such as in pumps.

The magnetic fluid seal can also be executed as an axial magnetic fluid seal.

Then the magnet is disc-shaped, the pole pieces are disc-shaped and placed at a radially different distance from the shaft, and the magnetic conducting component is a disc, which is arranged opposite the pole pieces, the pole pieces comprising annular ridges at a short distance from the disc, the magnetic fluid being arranged between the pole pieces and the disc, and either the magnet or the disc being connected to the shaft, and the other being connected to the housing. An advantage of this embodiment is that the magnet and the disc can easily be positioned at a short distance from each another. Just as with the radial magnetic fluid seal no wear occurs. As the build-up of pressure in an axial direction has to be compensated, the components have to be made heavier to avoid bending and the axial seal will be larger than the radial seal.

A spring element is advantageously arranged near the axial magnetic fluid seal, which presses the magnet with pole pieces and the disc against each another, inducing a zero slot. Consequently, a very high tightness of the magnetic fluid seal arises. Attendant effects such as an additional moment and wear will be small due to the lubricating effect of the magnetic fluid.

To ensure that the magnetic fluid seal can also stem liquids, for example after the bellows has failed, a conventional dynamic seal has been incorporated in the grooves between the ridges and/or between the pole pieces. The conventional dynamic seal, such as an O-ring or another sort of packing, is lubricated by the magnetic fluid so friction ancl wear will hardly occur. The pressure tightness of the seal is enhanced by this measure.

Beyond the secondary seal a fireproof shut-off ring is also advantageously arranged, which is arranged about the shaft, and which is manufactured from a memory metal, the ring, when in a cold state having been given a shape in which the shaft is free-running, and which in the case of fire adopts a shape such that it closes against the shaft and the housing.

The fact is that in the case of fire the secondary seal will no longer operate completely, seeing as the bellows will fail and the magnetic fluid disappears. To prevent the escaped fluid from still making its way into the surroundings the ring made of memory metal is arranged.

Advantageously a fireproof seal of that sort is also arranged in front of the secondary seal. In this way it is ensured that after a fire the secondary seal with the leaked fluid can easily be replaced.

The fireproof seal preferably changes its shape at a temperature which is lower than the critical temperature where the secondary seal fails, for example 120-170° . The ring advantageously has a one-way shape memory and does not return to the shape of its cold state when it cools after heating. After the fire the leaked-out fluid is then retained in the housing of the secondary seal.

Beyond the secondary seal a conventional dynamic seal is advantageously arranged about the operating shaft. If the secondary seal fails, the fluid leaked along the primary seal will thus not find its way into the surroundings. A monitoring system is advantageously arranged, which gauges the pressures which occur in front of and beyond each part of the secondary seal, to determine the occurrence and the rate of leakage in order to carry out maintenance. So it is ensured that maintenance can be carried out when the leakage has reached a certain level or when the secondary seal or a part thereof fails. The monitoring system advantageously comprises pressure gauges, and a membrane is arranged in the housing near the bellows to control the operation of the bellows. The membrane is arranged between the space which connects to the primary seal and a pressure gauge and is made of the same flexible material as the bellows. By means of the pressure gauges the extent of leakage of the seals can be determined. The membrane has been added to check whether the bellows is still intact. In the case of a construction with a proportional volume beyond the bellows and the membrane in relation to their surface and thickness, the pressures beyond the bellows and beyond the membrane are equal in the case of a functioning bellows. If the bellows has failed, then the pressure beyond the bellows is higher than the pressure beyond the membrane.

The pressures are advantageously gauged ahead of and between the pole pieces, thus determining the carrying out of maintenance or not and the possible occurrence of leakage. If the pressure between the pole pieces is zero, in other words equal to the ambient pressure, then no leakage will occur into the surroundings. If this pressure is larger than zero then the escaped fluid has to be discharged, the possibility of leakage to the surroundings being present. If the pressure ahead of the pole piece goes above a certain value, then the leaked fluid should be discharged to prevent leakage of the magnetic fluid seal starting.

The pressure between the secondary seal and the conventional seal is advantageously gauged. If this pressure is higher than zero, then maintenance should be carried out immediately because leakage will take place into the surroundings. The conventional seal limits the extent of the leakage. The bellows, the magnetic fluid and the fireproof shut-off ring can also be used separately for sealing the shaft of a valve.

The present invention will now, by way of example, be described with reference to embodiments, as shown in the accompanying drawings. Fig. 1 is a simplified representation of the valve according to the invention.

Fig. 2 to 7 show various embodiments of the bellows seal according to the invention, which is a part of the valve according to fig. 1.

Figs. 8 and 9 show various embodiments of a magnetic fluid seal, which is a part of the valve according to fig. 1. Figs. 10 and 11 show fireproof seals in a cold and heated state, as these can be incorporated in the valve according to fig. 1.

Fig. 1 shows that the valve according to the invention is incorporated in a pipe 1, and comprises a housing 2, the lowest portion 2 A of which is placed in the pipe 1, and in which a rotatable shut-off element 3 is arranged. The shut-off element 3 is rotated with an operating shaft 4, which with the help of a primary seal 5 seals the fluid present in the pipe 1 vis-a-vis the surroundings. The fluid can be a chemical, liquid, gas, vapor or liquefied material. It will be understood that instead of being incorporated in a pipe, the valve can be connected to a reservoir.

On the portion of the housing 2 A a portion of the housing 2B is placed, in which the bellows seal 6 is incorporated. On the portion of the housing 2B a portion of the housing 2C is placed, in which the magnetic fluid seal 7 is incorporated. The bellows seal 6 and the magnetic fluid seal 7 together form the secondary seal. Above and below the secondary seal fireproof shut-off rings 8 and 9 are arranged. Beyond the secondary seal a conventional seal 10 is arranged. All the seals are placed about the operating shaft 4.

With the help of pressure gauges Ml to M5 a monitoring system gauges the pressure, ahead of, beyond and in-between the components of the secondary seal. In the portion of the housing 2B of the bellows seal 6 a membrane 11 is arranged, behind which a pressure gauge M2 is placed. The components of the seal which are of importance will be discussed separately below.

The figures 2 to 7 show different embodiments of the bellows seal 6 as shown in fig. 1.

Fig. 2 shows the bellows seal 6A, the bellows 12 being 10 completely made of flexible material and the pressure of the fluid that has leaked along the primary seal 5 will be exerted on the outer side of the bellows. For that reason in this embodiment of the bellows seal a coiled spring 13 is arranged between the bellows 12 and the operating shaft 4 which runs along the whole length of the bellows. With the help of a bush 19 one side of the bellows is clamped to a flange 16 welded to the shaft and the other side of the bellows is clamped to the housing 2B with the help of a flange 17. Locking against loosening of the bellows is ensured with the help of annular cams 18 attached to the flanges 16 and 17. Locking between flange 16 and shaft 4 and flange 17 and housing 2B, respectively, can be guaranteed by fixing means yet to be specified more closely. The outer ends of the coiled spring 13 are incorporated near the flange 16 in the shaft 4 and near the flange 17 in this flange. Instead of a conventional seal 10 a similar conventional seal 24 can be incorporated into the flange 17 if no use is made of a magnetic fluid seal 7.

Fig. 3 shows a second embodiment 6B of the bellow seal 6. With this seal the outer end 20 of the bellows to be attached to the shaft is of metal, and this metal outer end is attached to the shaft 4 with the help of a pin 21. Sealing of the metal outer end onto the shaft is obtained by conventional static seals 22. In this embodiment the coiled spring 13 only runs along the flexible portion of the bellows. Otherwise this embodiment is the same as that of fig. 2.

Fig. 4 shows an embodiment 6C of the bellow seal 6 with a metal outer end 20 of the bellows, which is welded to the shaft 4. Attaching the flexible portion of the bellows to the housing 2B takes place here by vulcanizing the flexible portion of the bellows to the housing. For this purpose the flexible portion of the bellows has to made substantially of rubber. Attaching the flexible portion of the bellows to the metal outer end 20 can also take place by vulcanization. The coiled spring 13 is incorporated in the seal in a manner analogous to that of fig. 3.

Fig. 5 shows an embodiment 6D of the bellows seal 6, in which the coiled spring 13 is incorporated in the flexible portion of the bellows 12. Otherwise this embodiment is the same as that of fig. 4.

Fig. 6 shows an embodiment 6E of the bellows seal 6 in which instead of a coiled spring a synthetic 26 with a very low friction coefficient is arranged between the flexible portion of the bellows 12 and the shaft. A lubricating fluid 27 is applied between the synthetic 26 and the flexible portion of the bellows. Otherwise this embodiment is the same as that of fig. 5. Fig. 7 shows an embodiment 6F of the bellows seal 6, in which the bellows does not have a metal outer end, but the flexible outer ends of the bellows 12 are provided with metal rings 28 and 29. Here, as in the embodiment of fig. 6, a synthetic 26 with a very low friction coefficient is applied between the bellows 12 and the shaft 4. It will be apparent that the different attaching methods and the presence or otherwise of a metal outer end or a metal ring on one or both outer ends of the bellows can be used in all embodiments according to the figures 2 to 7. It will also be apparent that in the figures 2, 3, 4, 6 and 7 the coiled spring or the synthetic with a low friction coefficient can be arranged between the bellows and the housing, if the pressure of the leaked fluid is exerted on the inner side of the bellows.

Fig. 8 shows a radial magnetic fluid seal 7 with a permanent magnet 30, two pole pieces 32 and 33 with several annular ridges 34 placed at a short distance from the shaft 4. Between the pole pieces and the shaft 4 a magnetic fluid 31 is applied, as a result of which there is a closed magnetic circuit. The magnetic fluid 31 consists of a fluid in which magnetizable particles are incorporated. A conventional dynamic seal such as an O-ring 41 or a packing 42 of a different kind can be arranged between the ridges of the pole pieces or between the pole pieces themselves.

Fig. 9 shows an axial magnetic fluid seal. The permanent magnet 35 is annular and arranged on the shaft. The pole pieces 36 and 37 are disc-shaped and arranged at different distances from the shaft on the permanent magnet 35, at a short distance from a disc 38, which is attached to the housing 2C. The pole pieces 36 and 37 have annular ridges 39, and the magnetic fluid 31 is applied between the pole pieces and the disc 38. In this way a magnetic circuit is formed which does not run through the shaft. With the help of a spring element 40 the disc 38 can be pressed against the ridges 39 of the pole pieces 36 and 37, as a result of which a very strong magnetic field is formed. Here too conventional dynamic seals such as an O-ring 41 or a packing 42 of a different kind can be arranged between the ridges 39 of the pole pieces 36 or 37 or between the pole pieces .

Fig. 10 shows a fireproof seal ring 8/9, the left side of the figure representing the ring in a cold state and the right side of the figure representing the ring in a heated state. In the cold state the shaft 4 runs freely through the ring 8/9. The ring is made of a material with a one-way shape memory, as a result of which in the case of fire the ring takes on the shape according to the right side of fig. 10 above the critical temperature of the secondary seal, for example 120- 170 °C. Due to this change in shape the ring clamps around the shaft 4 and in the housing 2, so that a complete shut-off is obtained. Upon cooling after the fire the ring retains the shape which it took on in the heated state. Fig. 11 shows another embodiment of the fireproof seal ring. This ring was originally a conical one (at the right in the figure) which has been made cylindrical by butting the lower, wide portion and stretching the upper, narrow portion. The lattice structure here is such that upon heating the ring passes from the shape, on the left in the figure, to the original conical shape on the right in the figure and then a complete seal is provided.

The parts of the housing 2A, 2B and 2C are sealed vis-a-vis one another by fireproof static seals. This is not shown.

The operation of the seal will now be described with reference to fig. 1. In order to open and close the seal the shut-off element 3 has to be rotated about an angle of usually approximately 90° with the help of the operation shaft 4. The primary seal 5 on the shaft 4 will seal off the fluid in the pipe 1 in which a certain working pressure of, for example, 16 bar can prevail. The leakage along this seal is generally very low, for example smaller than 10^'8 mbarl/s. Because of wear, however, this seal can start leaking. In the course of time the pressure between the primary seal and the bellows seal will, for that reason, rise, and if the primary seal fails the pressure can here, too, adopt the working pressure. The bellows seal will have to stem this leakage, while the operating shaft 4 should still be operable with small moment. For that reason the coiled spring or the synthetic with a low friction coefficient is arranged in the bellows seal on the inner side of the bellows or a coiled spring is incorporated in the bellows, as a consequence of which the additional moment, even under high pressure, is mainly determined by the torsion of the flexible portion of the bellows. The bellows seals off against fluids, but is not entirely hermetic for vapors or gasses, because diffusion through the material can occur. In order to stop this diffusion leakage of the flexible bellows the magnetic fluid seal 7 is put into place. If the distance between the ridges and the shaft or the distance between the ridges and the disc is smaller than 0, 1 mm, the magnetic fluid at every ridge can stem a pressure difference of approximately 0,5 bar. At a higher difference in pressure the magnetic fluid is pushed aside and gas or vapor will pass, but when the difference in pressure again gets lower than 0,5 bar the magnetic fluid will automatically restore the seal at the ridge. When using sufficient ridges the magnetic fluid seal will stem the vapors or gases entirely, a leakage of less than 10-9mbarl/s as a consequence of diffusion of the vapors or gases through the magnetic fluid being feasible.

Because liquid too can get to the fluid seal when the bellows seal fails, a conventional dynamic shaft seal is included between, for example, the first and the second ridge, as seen from the bellows seal. In order that the leaked fluid does not enter the surroundings directly if the magnetic fluid seal should unexpectedly fail, a conventional dynamic seal 10 is included in the housing beyond the magnetic fluid seal.

Beyond the conventional dynamic seal 10 and ahead of the bellows seal 6 fireproof sealing rings 8 and 9 are arranged about the shaft, since in the event of fire the bellows seal 6 and the magnetic fluid seal 7 will fail. Under the higher temperature of the fire the fireproof sealing rings will, however, seal the valve hermetically, so that no fluid will leak into the surroundings.

In order to determine the extent of leakage of the primary seal and the bellows seal and the magnetic fluid seal, so that timely maintenance can be done, and in order to be able to observe deterioration of one or more of the seals, so that appropriate maintenance and repairs can be planned, the pressure gauges Ml to M5 are arranged so as to be able to gauge the pressure of the leaked fluid at the various places ahead of and behind the seals. The gauged pressures at the various pressure gauges are named PI to P5, respectively. If the pressure P4 is higher than 0, then the magnetic fluid seal is leaking and there should be immediate intervention. If the pressure P5 is higher than 0, but the pressure P4 remains 0, there is a chance of leakage into the surroundings and maintenance should be carried out in due course. On the basis of pressure P3 it can be determined whether the pressure in front of the magnetic fluid seal is so high that controlled discharge of the leaked fluid has to take place.

With the help of the pressure P2 it can be determined whether the bellows is intact. If PI is greater than P3, then this means that the bellows seal is intact. If the difference in pressure between PI and P3 is 0, then this can mean that the bellows seal has failed, but it can also mean that the primary seal is no longer leaking. In order to determine this, the membrane 11 is arranged, the membrane being made of the same material as the flexible bellows and through which as much fluid diffuses as through the bellows 6. With the help of the pressure P2 beyond the membrane 11 it can now be determined whether the bellows seal 6 is functioning, that being the case if P2 is equal to P3. If the bellows has failed P3 will be equal to PI , but P3 will be greater than P2. Only if the leakage via the primary seal was and is 0 and the bellows fails can this not be detected, seeing as the pressures PI, P2 and P3 are then all equal to one another. If, however, in this situation the primary seal begins to leak, this can be immediately detected because PI and P3 are then greater than 0 and P3 is greater than P2.

The operation of the primary seal is determined on the basis of pressure PI.

The valve is designed for a lifespan in which the shut-off element can be opened and closed at least 50,000 times. Seeing as the primary seal could fail directly after having come into use, the bellows seal has to be able to resist the working pressure throughout its whole lifespan. The embodiment of the bellows with the coiled spring is therefore advantageous, in that a sufficiently large number of windings, preferably a minimum of 10-12, run along the flexible material and that they have a circular cross section and rest next to each other, as a result of which the flexible material is not pressed between the windings and is not cut into, and as a consequence of which hardly any or no wear of the bellows and friction between the bellows and the coiled spring will occur when the operating shaft is rotated.

In order to keep the emission into the surroundings as limited as possible in the event of the secondary seal unexpectedly failing, the space between the housing and the operating shaft with the seals should be as small as possible.

Claims

1. Valve for a pipe or reservoir, comprising a housing , a shut-off element, a rotatable operating shaft which runs through the housing, and a primary seal on the shaft, characterized in that the valve comprises a secondary seal, which, as seen from the shut-off element (3), is placed beyond the primary seal (5) about the shaft (4) and comprises a bellows (12), substantially manufactured from a flexible material, one end of the bellows (12) being attached to the shaft (4) and the other end to the housing (2B), the bellows (12) permitting the shaft (4) to rotate along a part of a revolution, and with that twists, and a coiled spring (13) being arranged on the side of the bellows (12) which is turned away from the space connected to the primary seal (5), which coiled spring supports the bellows (12), which coiled spring is manufactured from a substantially circular thread, which coiled spring is at least as long as the twisting portion of the bellows (12), and which coiled spring is attached with one end to the shaft (4) and with the other end to the housing (2B) in order to obtain a torsion which substantially corresponds to that of the bellows (12).

2. Naive for a pipe or reservoir, comprising a housing , a shut-off element, a rotatable operating shaft which runs through the housing, and a primary seal on the shaft, characterized in that the valve comprises a secondary seal, which, as seen from the shut-off element (3), is placed beyond the primary seal (5) about the shaft (4) and comprises a bellows (12), substantially manufactured from a flexible material, one end of the bellows (12) being attached to the shaft (4) and the other end to the housing (2B), the bellows (12) permitting the shaft (4) to rotate along a part of a revolution, and with that twists, the flexible material of the bellows (12) incorporating a coiled spring (13), supporting the bellows (12), the windings of which rest free from one another, and which coiled spring is equally long as the twisting portion of the bellows (12).

3. Naive for a pipe or reservoir, comprising a housing, a shut-off element, a rotatable operating shaft which runs through the housing, and a primary seal on the shaft, characterized in that the valve comprises a secondary seal, which, as seen from the shut-off element (3), is placed beyond the primary seal (5) about the shaft (4) and comprises a bellows (12), substantially manufactured from a flexible material, one end of the bellows (12) being attached to the shaft (4) and the other end to the housing (2B), the bellows (12) permitting the shaft (4) to rotate along a part of a revolution, and with that twists, and a synthetic (26) having a very low friction coefficient being arranged on the bellows on the side of the bellows (12) which is turned away from the space which connects to the primary seal (5), allowing support of the bellows (12) against either the shaft (4), or the housing (2B).

4. Valve according to claim 3, characterized in that a lubricating fluid (27) is applied between the synthetic (26) with a very low friction coefficient and the flexible bellows.

5. Naive according to claim 1, characterized in that the windings of the coiled spring rest against one another.

6. Valve according to any one of the claims 1 to 5, characterized in that the bellows (12) is in its released state between the opened and closed position of the shutoff element (3), preferably halfway through the total angle of rotation of the operating shaft (4).

7. Valve according to claim 6, characterized in that the total angle of rotation of the operating shaft (4) is approximately 90° .

8. Valve according to claim 1 or 5, characterized in that the total angle of rotation of the operating shaft (4) is approximately 90° , that the bellows (12) is in its released state halfway through the angle of rotation, and that the coiled spring (13) has at least approximately 10-12 windings along the twisting portion of the bellows (12).

9. Valve according to any one of claims 1 to 5 or 7, characterized in that the bellows (12) is circularly cylindrical.

10. Valve according to any one of claims 1 to 5 or 7, characterized in that the bellows (12) is manufactured substantially from rubber.

11. Valve according to any one of the claims 1 to 5 or 7, characterized in that the bellows (12) is manufactured substantially from a synthetic, preferably a PTFE/PFA synthetic.

12. Valve according to any one of the claims 1 to 5 or 7, characterized in that the bellows (12) is manufactured substantially from a laminate of synthetics and/or rubbers.

13. Valve according to any one of claims 1 to 5 or 7, characterized in that the end (20) of the bellows which is to be attached to the shaft is of metal, to which the flexible part of the bellows (12) is attached, the metal end (20) and the shaft (4) being statically sealed relative to each other, for example with the help of O-rings.

14. Valve according to claim 13, characterized in that the other end of the bellows (12) is also of metal.

15. Valve according to claim 14, characterized in that the metal end is attached to either the shaft (4) or the housing (2B) with the help of a pin (21).

16. Valve according to any one of the claims 1 to 5 or 7, characterized in that the flexible end of the bellows (12) is attached to either the shaft (4) or to the housing (2B) by clamping.

17. Valve according to claim 16, characterized in that the flexible end of the bellows (12) is provided with a metal ring (28, 29).

18. Valve according to claim 10, characterized in that the flexible end of the bellows (12) is attached to either the shaft (4) or the housing (2B) by vulcanizing.

19. Valve according to claim 1, characterized in that the secondary seal also comprises a magnetic fluid seal (7), which, as seen from the shut-off element (5), is arranged beyond the bellows (12) about the shaft (4).

20. Valve according to claim 19, characterized in that the magnetic fluid seal (7) comprises at least one magnet (30), magnetic liquid (31), a magnetic conducting component, and two pole pieces (32, 33) on both sides of the magnet, the magnet (30), the pole pieces (32, 33), the magnetic fluid (31) and the component forming a closed magnetic circuit.

21. Valve according to claim 20, characterized in that the magnetic conducting component is the shaft (4) itself, that the shaft (4) is round, and that the magnet (30) and the pole pieces (32, 33) are arranged annularly about the shaft (4), the pole pieces (32, 33) comprising various annular ridges (34), which are at a short distance from the shaft (4), and the magnetic fluid (31) spanning the distance between the ridges (34) and the shaft (4).

22. Valve according to claim 20, characterized in that the magnet (35) is disc-shaped, that the pole pieces (36, 37) are disc-shaped and are placed at a radially different distance from the shaft (4), and that the magnetic conducting component is a disc (38), which is arranged opposite the pole pieces (36, 37), the pole pieces (36, 37) comprising angular ridges (39) at a short distance from the disc (38), the magnetic fluid (31) being arranged between the pole pieces (36, 37) and the disc (38), and either the magnet (35) or the disc (38) being connected to the shaft (4), and the other being connected to the housing (2C).

23. Valve according to claim 22 , characterized in that a spring element (40) is arranged, which presses the magnet (35) with pole pieces (36, 37) and the disc (38) against each other, inducing a zero slot.

24. Valve according to claim 21, characterized in that a conventional dynamic seal (41, 42) is incorporated in the grooves between the ridges (34, 39) and/or between the pole pieces (32, 33 and 36, 37, respectively).

25. Valve according to claim 20, characterized in that the magnetic fluid (31) contains a very high concentration of magnetizable particles.

26. Valve according to claim 1 , characterized in that a fireproof shut-off ring (8) is also arranged beyond the secondary seal, said ring being arranged about the shaft and being manufactured from a memory metal, the ring, when in a cold state, having been given a shape in which the shaft (4) is free-running, and which, in the case of fire, adopts such a shape that it closes against the shaft (4) and the housing (2).

27. Valve according to claim 26, characterized in that such a fireproof shut-off ring (9) is also arranged in front of the secondary seal.

28. Valve according to claim 26, characterized in that the ring (8, 9) changes its shape at a temperature of between 120° and 170°C.

29. Valve according to claim 26, characterized in that the ring (8, 9) has a one-way shape memory and that when it cools after heating it does not return to the shape of its cold state.

30. Valve according to any one of claim 1 to 5 or 7, characterized in that beyond the secondary seal a conventional dynamic seal (10) is arranged about the operating shaft.

31. Valve according to any one of claim 1, characterized in that a monitoring system is arranged, which gauges the pressures which occur in front of and beyond each part of the secondary seal, to determine the occurrence and the rate of leakage in order to carry out maintenance.

32. Valve according to claim 31, characterized in that the monitoring system comprises pressure gauges (Ml, M2, M3, M4), and that a membrane (11) is arranged in the housing (2B) of the bellows (12) between the space which connects to the primary seal (5) and a pressure gauge (M2), which is made of the same flexible material as the bellows, so as to control the operation of the bellows (12).

33. Valve according to claim 32, characterized in that when using a magnetic fluid seal (7) a pressure gauge (M5) gauges the pressure between the pole pieces (32, 33 and 36, 37, respectively), so that in combination with pressure gauge (M3) the operation of the magnetic fluid seal can be controlled.

34. Bellows for sealing the shaft of a valve according to any one of the claims 1 to 5 or 7.

35. Magnetic fluid seal for sealing the shaft of a valve according to any one of the claims 19 to 25.

36. Fireproof shut-off ring for shutting off the shaft of a valve according to any one of the claims 26 to 29.

37. Monitoring system for controlling the primary and secondary seal, or portions thereof, according to any one of the claims 31, 32 or 33.