WO1992016779A1 - A large gate isolation valve, particularly for vacuum systems for nuclear fusion machines and similar uses - Google Patents

Abstract

A large isolation valve, particularly for vacuum systems for nuclear fusion plants and similar uses, includes a body (2) with two annular valve seats (9) which cooperate with two obturators (5) carried by a gate unit (4). Actuators (16, 18) for moving the obturators (5) and the valve seats (9) towards and away from each other are separate from and independent of the actuators (6, 12) for moving the gate unit (4) and include a ring of thrust springs (16) which act so as to move the two obturators (5) apart axially towards the closure position, and a ring of pressurised-fluid actuators (18) which can be activated in order to move the two obturators (5) together axially towards the open position.

Description

A _large gate isolation valve, particularly for vacuum systems for nuclear fusion machines and similar uses The present invention relates in general to large isolation valves for vacuum systems for nuclear fusion plants and similar uses.

In particular, the invention relates to a .gate isolation valve of the type including a body with two coaxial ducts for sealingly connecting respective pipes and two annular valve seats which are associated with the inner ends of the ducts and cooperate with two opposed valve obturators carried by a gate body which is movable in the valve body along a line perpendicular to the axis of the ducts between a retracted position (in which the vϋlve is open) and an extended position (in which the valve is closed) , and actuator means for moving the gate body between its retracted and extended positions and for moving the obturators and the valve seats axially towards and away from each other.

When such a valve is used for the isolation and regeneration of a cryogenic pump for producing a vacuum in the toroidal chamber of a nuclear fusion machine, or for similar uses in plants using corrosive or harmful fluids, or in any environment which is under vacuum and with which the use of lubricants or, in any case, contaminant substances is incompatible, the valve structure is subject to certain extremely restrictive requirements.

In the first place, it is absolutely necessary for the valve to be able to ensure a perfect hermetic seal in the closed condition, even in the event of damage to its control system. This requirement must be guaranteed over a period of time, even after many closure/opening cycles.

Moreover, the moving parts of the valve must be free of lubricants which could in any way enter the region controlled thereby with the consequent risk of contamination.

Another basic requirement for these valves is that their components must be easy to remove remotely, that is, with remote handling devices.

Finally, there is also a need for compactness axially of the pipes which are connected by the ducts in the body with which the valve seats are associated.

In known isolation valves of the type indicated above, this set of requirements is not generally observed since some of them are incompatible with others. Conventionally, the gate body is moved between its retracted and extended positions and the obturators are opened and closed relative to the valve seats by means of a single kinematic mechanism of the parallelogram type with resilient toggles or equivalent systems which close and open the obturators relative to their valve seats during the final portion of the extension of the gate body and during the initial portion of its retraction, respectively.

These operating systems inevitably involve relative sliding between the obturators and the valve seats and consequently the risk of premature wear of the sealing members between them. Moreover, such mechanisms are generally complex from a structural point of view and, furthermore, are not very reliable in operation because it is difficult, if not* impossible, to lubricate them effectively; moreover, they generally make the valve quite bulky axially of the pipes which are connected to the coaxial ducts in the body in use.

In order to prevent the aforementioned problems, the subject of the present invention is a large isolation valve of the type defined above, the essential characteristic of which lies in the fact that the obturators and their seats in the valve body are moved towards and away from each other by actuator means which are separate from and independent of the actuator means for moving the gate body, are interposed axially between the obturators, and include a ring of thrust springs which act so as to move the two actuators axially away from each other towards the closure position and a ring of pressurised-fluid actuators which can be activated in order to move the two obturators together axially towards the open position.

By virtue of this concept, the movements of the gate body and of the two obturators carried by the body are achieved by means of two distinct movements, the first perpendicular to the axis of the valve seats and the second along those axes. The movements of the obturators and their seats towards and away from each other upon closure and opening thus take place without sliding, preventing any risk of wear of the sealing members. Moreover, the arrangement of the actuator means for moving the obturators away from and towards each other (the thrust springs and the fluid actuators, respectively) considerably reduces the size of the valve axially of the ducts in the body, on the one hand, and, on the other hand, enables the valve to be kept both in the open position and in the closed position with the actuator means de-energised. In fact, the actuator means for moving the gate body and the pressurised-fluid actuators associated with the two obturators need to be activated only during the dynamic phases of the valve.

A further advantage resulting from the arrangement of the valve according to the invention consists of the fact that all the kinematic members which require lubrication can be effectively isolated, thus ensuring their efficiency and reliability over a period of time without the risk of contaminating the plant for which the valve is used.

According to a preferred embodiment of the invention, the two obturators are constituted by circular plates each having a flat, radially-outer region which carries a pair of concentric annular face seals for cooperating with the respective annular valve seat, and a substantially concave, radially-inner region the concavity of which faces the respective valve seat.

This conformation gives a certain degree of flexibility to the two obturators in order to compensate for any misalignment or deformation, ensuring an optimal, stable and uniform distribution of the sealing pressure when the valve is in the closed condition.

Conveniently, the ring of pressurised-fluid actuators includes two groups of alternate actuators, each group being associated with a respective, substantially annular supply manifold connected to a pressurised-fluid supply. To advantage, the manifolds are arranged concentrically between the two obturators.

Further characteristics and advantages of the invention will become clear in the course of the detailed description which follows with reference to the appended drawings, provided purely by way of non-limiting example, in which:

Figure 1 is a partially-sectioned, schematic, perspective view of an isolation valve according to the invention.

Figure 2 is a partial, longitudinal, sectional view of Figure 1,

Figure 3 is a partially-sectioned side elevational view taken on the arrow III of Figure 2,

Figure 4 shows the detail indicated by the arrow IV in Figure 2, on an enlarged scale.

Figure 5 shows the detail indicated by the arrow V in Figure 4, on an enlarged scale.

Figure 6 is a section taken on the line VI-VI of Figure 2, on an enlarged scale.

Figure 7 is a section taken on the line VII-VII of Figure 2, on an enlarged scale.

Figure 8 shows the detail indicated by the arrow VIII of Figure 2 in section and on an enlarged scale.

Figure 9 is a view of the detail indicated by the arrow IX of Figure 7, on an enlarged scale,

Figure 10 is a section taken on the line X-X of Figure 5, on an enlarged scale, and Figure 11 is a section taken on the line XI-XI of

Figure 5, on an enlarged scale.

With reference to the drawings, a large valve, generally indicated 1, is intended, in particular, for isolating a cryogenic vacuum pump for the toroidal plasma chamber of a magnetic-confinement nuclear fusion machine during its periodic regeneration and maintenance. It should be noted, however, that the valve 1 may be used as a large shut-off valve in plants of other kinds, for example, for treating corrosive or harmful fluids, etc., and, in any case, in vacuum systems with particularly restrictive requirements as regards the need for parts of the shut-off unit to be sealed and not contaminated.

The valve 1 is composed essentially of the following elements: a body 2 with an end cover 3, a gate unit 4 carrying two valve obturators 5, and an operating shaft 6 for operating the gate unit 4.

The body 2 is constituted by a sheet-steel structure with reinforcing ribs, with a generally flat, parallelepipedal shape, the ends of its larger faces which are furthest from the cover 3 each having a coaxial circular aperture defined by a respective annular connector flange 7 which is intended to be fixed sealingly, in conventional manner, to a respective pipe, only one of which is indicated 8 in Figure 1. In the embodiment illustrated, the pipe 8 is intended to be connected to the intake side of a cryogenic pump and the other pipe (not shown) is intended to be connected to the toroidal chamber of the nuclear fusion machine. The inner end faces of the two annular flanges 7 define two opposed annular valve seats 9 which cooperate with the two obturators 5, in the manner which will become clearer from the following.

Two internal metal sliding guides 10 extending along the smaller side walls of the body 2 are accessible from outside by means of the cover 3 which is fixed removably to the body 2. The cover 3 supports a framework 11 carrying an actuator for operating the gate unit 4, the actuator being constituted, in the embodiment illustrated, by an electric motor 12 with a reduction unit which rotates a female-threaded member (not shown) which- engages an external thread 40 on the operating shaft 6. The shaft 6 may be driven in opposite directions by a motor or by a cylinder/piston operated by pressurised fluid.

The length of the body 2 is such that the gate unit 4 can be moved within it between its extended position shown in the drawings (in which the valve is closed) , in which it is situated in correspondence with the apertures defined by the two annular flanges 7, and a retracted position (in which the valve is open) in which it leaves the duct between the apertures free. Its thickness is the minimum necessary to house the gate unit 4 which, as can clearly be seen from the drawings, is particularly small.

The fact that the cover 3 is fixed removably enables remote handling equipment to gain access to the interior of the body 2 so that it is possible both to inspect and possibly repair the sliding guides 10 and to remove the gate unit 4 with its shaft 6 completely for normal maintenance. The gate unit 4 is constituted by the two obturators 5 and a peripheral annular support element 13 which is interposed between the obturators and carries two pairs of transverse appendages 14, the ends of which form respective sliding blocks 15 which are in sliding contact with the guides 10.

The two obturators 5 are constituted by respective metal plates each having a flat, radially outer portion 5a and a slightly concave, radially inner portion 5b, the concavity of which faces the corresponding annular connector 7. The outer portion of the surface of the radially outer region 5a has two concentric circular grooves 14 with slightly different diameters, each housing an annular seal 15. The seals 15, which are conveniently of an organic material or of metal and have a geometry such as to make them very resilient, are resistant to temperatures of the order of 180 and to radiation and cooperate with the valve seats 9 of the respective connectors 7 when the obturators 5 are in the closed positions shown in the drawings.

The closed condition is normally maintained by the action of a ring of Belleville washers 16 which are housed in tubular bosses 17 on the annular support element 13 and act so as to move the two obturators 5 axially away from each other, compressing the seals against the seats 9 of the valve body.

A series of pneumatic actuators 18 is disposed in a ring within the ring of washers 16 for moving the two obturators 5 axially towards each other and thus moving them away from the valve seats 9. As shown in greater detail in Figure 9, each actuator 18 includes a first cylinder 19 with an end wall 20 carrying a central rod 21, the base of which is connected rigidly at 22 to the internal face of one of the two obturators 5, and a lateral skirt 23 carrying a pair of outer sealing rings

24. A second cylinder 26 has a lateral skirt 25 which is sealingly slidable axially outside the skirt 23, and an end wall 27 which is sealingly slidable on the rod

21. The skirt 25 is fixed peripherally to the internal face of the other obturator 5 by means of screws 28. The rod 21 is isolated by a bellows-like member 29 of which one end is fixed to the end wall 20 of the first cylinder 19 and the other end is fixed to the end wall 27 of the second cylinder 26.

The two cylinders 19 and 26 of each actuator 18 define a thrust chamber 30 which is connected, by means of a respective pipe 31, to an annular manifold 32 interposed coaxially between the two obturators 5.

In fact, there are two annular manifolds 32, one arranged concentrically within the other, and each connected to alternate pneumatic actuators 18. In other words, the ring of actuators 18 is divided into two alternate groups which are connected respectively to one manifold 32 or to the other so that they can be activated independently and selectively.

Naturally, the admission of pressurised fluid to the thrust chambers 30 through the respective manifolds 32 and pipes 31 moves the two cylinders 19, 26 of the fluid actuators 18 in question axially in opposite directions, so that the two obturators 5 are moved towards each other. In the absence of a supply to the thrust chambers 30, the washers 16 move the two obturators 5 apart, as stated above, and compress the seals 15 against the valve seats 9. A chamber 33, which is formed between the end wall 20 of the cylinder 19 of each pneumatic actuator 18 and the facing obturator 5 in the rest condition, is connected by a pipe 34 to a breather manifold 35 which is also interposed between the two obturators 5 adjacent the radially outer supply manifold 32 so that any operating fluid which leaks from the seals 24 is led out of the valve.

A further annular groove 36 intermediate the seats 14 in the surface of each obturator 5 is connected to a "leak-off" duct 37 in the respective annular connector 7 of the valve body. This leak-off duct enables the integrity of the seal of the valve obturator to be checked.

The annular support element 13 is normally constituted by two half-rings joined together and is connected rigidly to the lower end of the shaft 6 by a connecting block 38 and a hollow fixing member 39, in the manner shown in detail in Figure 5. Above this connecting region, in the embodiment illustrated, the shaft 6 has an external thread 40 which, as stated, engages a female-threaded member (not visible in the drawings) rotated by the motor-reduction unit 12. The shaft 6 is surrounded sealingly by a pair of external coaxial metal bellows 41 one disposed within the other (this duplication is to improve reliability) and is hollow so that a pair of tubes 42 can extend through it, one end of each tube being connected to a respective supply manifold 32 and its other end to a regulated pressurised-fluid supply unit, generally indicated 43.

As shown in greater detail in Figures 5 and 11, the breather manifold 35, however, is connected to a pipe 44 which is disposed beside the fixing member 39 and one end of which communicates with the space between the inner bellows 41 and the shaft 6, its other end communicating with a radial duct 45 which is formed in one of the obturators 5 and communicates with the chamber 33 of the fluid actuator 18 which is in an angular position corresponding to that of the pipe .44.

It is clear from the foregoing that all the mechanisms of the valve 1 which may require lubrication (the male-and-female thread of the shaft 6 and the regions of sliding between the cylinders 19, 26 of the pneumatic actuators 18) are isolated hermetically from the region which is in communication with the valve itself.

The valve operates as follows.

It is assumed that the valve starts in the closed configuration shown in the drawings, in which the gate unit 4 is disposed axially in correspondence with the connectors 7, with the obturators 5 kept in their closed positions against the respective valve seats 9 by the ring of washers 16: the valve is closed.

The first step consists of the admission of pressurised fluid to the thrust chambers 30 of one or other set of pneumatic actuators 18 or the other (or even to both sets) through the corresponding pipe 42 and the corresponding supply manifold 32. As a result of the pressure in the thrust chambers 30, the two obturators 5 are moved axially towards each other, moving their annular face seals 14 away from the valve seats 9.

The duplication of the system including the pneumatic actuators and the supply manifolds improves reliability.

At this point, the motor-reduction unit 12 is activated to retract the shaft 6, and hence the gate unit 4, which moves radially away from the connectors 7, thus opening the duct through the valve unit 2.

As soon as the gate unit 4 reaches its fully retracted position, the motor 12 is stopped and the pressurised fluid is discharged from the thrust chambers 30, causing the obturators 5 to move apart axially as a result of the action of the washers 16. The valve 1 thus remains open without the need for external energy.

In order to return the valve to the closed position, the steps described above are carried out in reverse: compressed air is first admitted to the chambers 30 of the actuators 18 so as to move the obturators 5 towards each other, after which the gate unit 4 is moved to its extended position in which it is axially in correspondence with the connectors 7 and, finally, the pressure is discharged from the thrust chambers 30, enabling the obturators 5 to move apart under the action of the washers 16 so as to bring the annular seals 14 sealingly into contact with the corresponding valve seats 9. The closed position of the valve is thus also maintained without the need for external energ .

Naturally, the details of construction and forms of embodiment of the valve may be varied widely with respect to those described and illustrated, without thereby departing from the scope of the present invention. Thus, for example, if the electric motor 12 is replaced by a fluid actuator, the valve may have position indicators and possibly travel-limit stops in the retracted and extended positions of the gate unit 4, respectively. Moreover, although the valve has been shown in a vertical position in the drawings, it is also suitable for use in any other position. Furthermore, according to a variant, not shown, the shaft 6 may be rotated rather than translated by^' the motor 12. In this case, a threaded portion of the shaft 6, which is sealingly isolated by means of an axial tube and bellows, is inserted in the gate unit 4 between the two obturators 5 and engages a female-threaded member carried by the annular element

13 for translating the unit 4. This solution has the advantage that the shaft 6 does not project from the valve body 2 when the valve is open, thus reducing the size of the valve.

Claims

1. A large isolation valve, particularly for vacuum systems for nuclear fusion plants and similar uses, including a body (2) with two coaxial ducts (7) for sealingly connecting respective pipes (8) and two annular valve seats (9) which are associated with the inner ends of the ducts (7) and cooperate with two opposed valve obturators (5) carried by a gate body (4) which is movable in the valve body (2) along a line perpendicular to the axis of the ducts (7) between a retracted position and an extended position, and actuator means for moving the gate unit (4) between its retracted and extended positions and for moving the obturators (5) and the valve seats (9) axially towards and away from each other, characterised in that the obturators (5) and their respective valve seats (9) are moved towards and away from each other by actuator means (16, 18) which are separate from and independent of the actuator means (6, 12) for moving the gate body {4) , are interposed axially between the obturators (5) , and include a ring of thrust springs (16) which act so as to move the two obturators (5) axially away from each other towards the closure position and a ring of pressurised-fluid actuators (18) which can be activated in order to move the two obturators (5) together axially towards the open position.

2. A valve according to Claim 1, characterised in that the two obturators (5) are constituted by circular plates each having a flat, radially-outer region (5a) which carries a pair of concentric annular face seals (15) for cooperating with the respective annular valve seat (9) and a substantially concave, radially-inner region (5b) the concavity of which faces the respective valve seat ( 9 ) .

3. A valve according to Claim 2, characterised in that the ring of pressurised-fluid actuators (18) includes two alternate groups of actuators, each group being associated with a respective substantially annular supply manifold (32) connected to a pressurised-fluid supply (43) .

4. A valve according to Claim 3, characterised in that the two supply manifolds (32) are disposed concentrically between the two obturators (5) .

5. A valve according to Claim 3 or Claim 4, characterised in that each pressurised-fluid actuator

(18) includes a first cylinder (19) carried by an axial rod (21) fixed to one of the obturators (5) and a second cylinder (26) which is fixed to the other obturator (5) and is slidable sealingly on the first cylinder (19) and along the rod (21) , the two cylinders

(19, 26) defining a sealed thrust chamber (30) which is connected to the respective supply manifold (32) .

6. A valve according to Claim 5, characterised in that the rod (21) is sealingly isolated by a bellows-like sealing member (29) .

7. A valve according to Claim 5, characterised in that each pressurised-fluid actuator (18) is connected, between the first cylinder (19) and the other obturator (5) , to a substantially annular breather manifold (35) disposed between the two obturators (5) .

8. A valve according to Claim 2, characterised in that the annular valve seats (9) have respective frontal leak-off ducts (36) disposed intermediate the regions of the contact between the valve seats (9) and the pairs of annular seals (15) of the obturators (5) .

9. A valve according to Claim 2, characterised in that the gate body (4) also includes a peripheral annular support element (13) which is interposed between the two obturators (5) and has a ring of axial seats (17) housing the thrust springs (16) , the annular support element (13) carrying block means (15) which can slide along corresponding longitudinal guides (10) of the valve body (2) and being connected to the actuator means (6, 12) for moving the gate unit (4) .

10. A valve according to Claim 9, characterised in that the actuator means for moving the gate unit (4) include a shaft (6) which extends in the body (2) parallel to and between the longitudinal guides (10) and has an end (38) which is connected to the annular support element (13) , and a motor (12) for driving the shaft (6) .

11. A valve according to Claims 3 and 10, characterised in that the motor (12) translates the shaft (6) and the shaft (6) is hollow, a pair of pipes (42) connected to the supply manifolds (32) extending through the shaft (6).

12. A valve according to Claim 11, characterised in that the shaft (6) is sealingly isolated by a pair of longitudinal bellows-like sealing members (41) .

13. A valve according to Claim 10, characterised in that the motor (12) rotates the shaft (6) .

14. A valve according to any one of the preceding claims, characterised in that the end of the body (2) furthest from the annular valve seats (9) has a removable cover (3) for affording access to the gate unit (4) and enabling it to be removed from the body

(2) by remote handling systems.