GB1604913A - Valves for process gas - Google Patents

Description

(54) IMPROVEMENTS IN VALVES FOR PROCESS GAS (71) We, BRITISH NUCLEAR FUELS LIMITED, of Risley, Warrington, Cheshire, a British company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: BACKGROUND OF THE INVENTION This invention relates to valves for process gas, and has particular application where the process gas is toxic, radio-active or valuable so that leakage into the environment must be reliably prevented, or where the ingress of ambient atmosphere into the process gas must be prevented to avoid reaction or for any other reason.

Known process gas valves designed to prevent leakage between the interior and exterior of the valve are generally provided with a bellows seal between the longitudinally movable valve closure member and the valve body. Such valves are referred to hereinafter as of 'the specified kind'. Should the bellows seal fail, however, such valves would be subject to leakage.

The present invention seeks to provide a bellows-sealed valve which is provided with additional safeguards against leakage in the event of bellows seal failure.

SUMMARY OF THE INVENTION According to the invention, a process gas valve of the hereinbefore specified kind has means for sealing its bellows seal at one end to the longitudinally movable valve closure member, means for sealing the other end of the bellows seal to an intermediate member, means for mounting and sealing said intermediate member fixedly in the valve body, a valve operating member having a screwthreaded blind bore, a screwthreaded stem of the valve closure member extending through said intermediate member with clearance and engaging said bore, the valve operating member being mounted for rotation in said intermediate member but being restrained against axial movement relative thereto, and means for sealing between said intermediate member and said valve operating member.

Said means for mounting and sealing said intermediate member fixedly in said valve body preferably includes at least two seals in tandem.

Said means for sealing between the fixed intermediate member and the rotatable valve operating member is preferably constituted by at least two seals in tandem, the total, but not necessarily individual, sealing integrity of the seals being as effective as an operative bellows seal i.e. 100% integrity. The innermost seal is preferably constituted by, in the closed position of the valve, the engagement of the valve closure member with its seat in the valve body, and in the valve open position, the engagement of a sealing surface of the valve closure member with a seat on the intermediate member. The next seal is conveniently provided by a pair of sealing thrust washers interposed between each plane face of a flange of the valve operating member and registering annular shoulders provided by an annular recess in the intermediate member.An additional, outer seal is conveniently constituted by an '0' ring seal mounted in the intermediate member and contacting an external cylindrical part of the valve operating member. An additional, outermost seal may be provided and be constituted by engagement with the valve body of a cover for the operating end of the valve.

The valve operating member preferably has its outer end formed exteriorly with a square or other convenient shape, enabling it to be turned with the aid of a complementary valve operating tool.

The valve operating member is preferably protected during non-use by said removable cover applied to the operating end of the valve body.

DESCRIPTION OF THE DRA WING A constructional example embodying the invention will now be described with reference to the sole Figure of the drawing accompanying the provisional specification, which is a side view in medial section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a valve 1 has a generally cylindrical body 2 with an axial inlet orifice 3 at its lower end and with which communicates an inlet pipe 4 welded or brazed to the body 2 at 5. The body 2 has a lateral outlet orifice 6 in its side and with which communicates an outlet pipe 7 welded or brazed to the body 2 at 8. The pipe 7 is curved so as to extend parallel to but spaced from the inlet pipe 4, but this is of course for convenience and is not essential.

That part of the body 2 which defines the inlet orifice 3 provides a valve seat 9 engageable by a washer 10 conveniently of P.T.F.E.

and mounted in an axial recess 11 in the head 12 of a valve closure member 13 by means of a recessed metal washer 14 and a peanedover central spigot 15 of the head 12. The washer bearing head 12 of the member 13 is axially movable with clearance in a bore 16 of the body 2. The remainder of the member 13 is constituted by a reduced-diameter shank 17 and a screwthreaded stem 18.

Between the shank 17 and the stem 18 is a coned annular surface 39. The annular clearance between the shank 17 and the bore 16 of the body 2 provides accommodation for a bellows 19, the lower end of which is annularly welded to the head 12 at 20, and the upper end of which is annularly welded at 38 to an annular intermediate member 21.

The member 21 is fixedly mounted in an enlarged bore part 22 of the body 2, there being an '0' ring seal 23 of neoprene trapped between the member 21 and the body 2 in the annular corner formed by the change of diameter of the body 2. The upper end part of the intermediate member has an externally-coned surface 24 into engagement with which the upper end 25 of the valve body is forced by inward swaging. An epoxy resin such as ARALDITE (R.T.M.) is applied to the surface 24 before swaging, and when swaging has been effected and the resin has set and hardened, a second seal to back up the seal 23 is produced.

The lower portion 26 of the intermediate member 21 has an enlarged bore 41 in its lower end changing, with a coned annular surface 42 complementary to the coned surface 39 of the member 13, to a smaller bore 43 clear of the screwthreaded stem 18 of the member 13. In the open position of the valve, the surfaces 39 and 42 are made to engage in sealing manner. The intermediate member 21 has an upper portion 26a having a bore 27 occupied by a cylindrical exterior of a valve operating member in the form of a cap 28, an '0' ring seal 29 of P.T.F.E. being provided therebetween and retained in an annular recess 30 in the portion 26a. The cap 28 is closed at its upper end and has a blindended screw-threaded bore 31 open at its lower end end and with which the screwthreaded stem 18 of the valve closure member 13 engages.The cap 28 has a flange 32 at its lower end and engaging an annular recess 33 in the intermediate member 21. The latter is laterally divided at the level of the recess 33 into the portions 26, 26a to facilitate assembly. Sealing thrust washers 34, 35 of P.T.F.E. are interposed between the plane upper and lower faces of the flange 32 and the walls of the recess 33, respectively. The exterior of the cap 28 is formed square to enable the cap 28 to be rotated by a suitable tool in order to operate the valve, the cap 28 being able to rotate but being restrained against axial movement by the engagement of the flange 32 in the recess 33 of the member 21, the latter being held fixedly in the body 2 by the swaging over of the upper end of valve body 2.Rotation of the cap 28 effects axial but not rotating movement of the valve closure member 13 to open or close the valve, the member 13 being held against rotation by one or more keys (one being shown, designated 36) projecting inwardly from the body 2 and loosely engaging respective keyways (one being shown, designated 40) in the head 12 of the member 13. This expedient avoids subjecting the bellows 19 to torsional stress.

A removable snap-on cover 37 (conveniently of a plastic such as polyethylene) for the upper end of the valve body 2 is provided to keep extraneous matter from the moving parts of the valve when the valve is not being operated.

The design philosophy of the described valve is that, in the particular application for which it was designed (and this application is not be considered its only application), the valve is intended to be used in large numbers, therefore it is regarded as expendable after a scheduled lifetime. Because of this, it is of simple construction and is relatively cheap to manufacture compared with purpose-made valves intended to have a long life. As regards its sealing integrity, the engagement of the normal main valve seal 10 on its seat 9 in the closed position of the valve, and the engagement of the coned surfaces 39, 42 in the open position of the valve, together with the bellows 19, provide full sealing integrity.

But if the bellows 19 should fail in operation, back-up sealing is also provided. It is well known that sealing between fixed components can be effected with a better degree of integrity than sealing between components which are relatively movable. Thus the prospective leakage path, should the bellows fail, between the body 2 and the fixed intermediate member 21 is effectively sealed by the trapped '0' ring seal 23 with back-up sealing provided by the swaged-over portion 25 of the body 2 contacting the coned surface 24 of the member 21 and further sealed with ARALDITE.The prospective leakage path between the member 21 and both the member 13 which is axially movable, and the cap 28 which is rotatable, relative to the member 21, is effectively sealed, should the bellows 19 fail, firstly by the main seal 10 of the valve in the closed position thereof and by the engagement of coned surfaces 39, 42 in the fully open position thereof (neither of these being effective should the bellows fail in an intermediate position of the valve closure member 13), secondly by the sealing effected by the engagement of the flange 32 with one or both of the sealing thrust washers 34, 35, thirdly by the '0' ring seal 29, and fourthly, in the case where ambient pressure is significantly greater than process gas pressure, by the sealing action of the cover 37 on the body 2.

Although neither of the seals involving in one case washers 34, 35 and in the other case seal 29, being seals between relatively rotatable parts, can individually be considered to be as effective as the seal provided by bellows 19, in aggregate their sealing function is effective to that extent, so that, should the bellows 19 fail, 100% integrity is maintained.

Valves according to the invention have one application (the particular application hereinbefore referred to) as process gas valves employed in the pipework involved in centrifuge cascades for the separation of the U235 and U23, isotopes of uranium, the process gas being uranium hexafluoride.

WHAT WE CLAIM IS: 1. A process gas valve having a valve body, a valve closure member longitudinally movable in the valve body, and a bellows seal between the valve closure member and the valve body for preventing leakage between the interior and exterior of the valve, characterised by means for sealing said bellows seal at one end to the longitudinally movable valve closure member, means for sealing the other end of said bellows seal to an intermediate member, means for mounting and sealing said intermediate member fixedly in said valve body, a valve operating member having a screw-threaded blind bore, a screwthreaded stem of the valve closure member extending through said intermediate member with clearance and engaging said bore, the valve operating member being mounted for rotation in said intermediate member but being restrained against axial movement relative thereto, and means for sealing between said intermediate member and daid valve operating member.

2. A valve according to claim 1, characterised in that said means for mounting and sealing said intermediate member fixedly in said valve body includes at least two seals in tandem.

3. A valve according to claim 1, characterised in that said means for sealing between said intermediate member and said valve operating member is constituted by at least two seals in tandem.

4. A valve according to claim 3, characterised in that the innermost seal is constituted by, in the closed position of the valve, the engagement of the valve closure member with its seat in the valve body, and in the valve open position, the engagement of a sealing surface of the valve closure member with a seat on said intermediate member.

5. A valve according to claim 3, characterised in that a non-innermost seal is constituted by a pair of sealing thrust washers interposed between each plane face of a flange of the valve operating member and registering annular shoulders provided by an annular recess in said intermediate member.

6. A valve according to claim 5, characterised in that an additional, outer seal is constituted by an '0' ring seal mounted in the intermediate member and contacting an external cylindrical part of the valve operating member.

7. A valve according to claim 5, characterised in that an additional, outermost seal is constituted by engagement with the valve body of a cover for the operating end of the valve.

8. A process gas valve, substantially as hereinbefore described with reference to the drawing accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. between the member 21 and both the member 13 which is axially movable, and the cap 28 which is rotatable, relative to the member 21, is effectively sealed, should the bellows 19 fail, firstly by the main seal 10 of the valve in the closed position thereof and by the engagement of coned surfaces 39, 42 in the fully open position thereof (neither of these being effective should the bellows fail in an intermediate position of the valve closure member 13), secondly by the sealing effected by the engagement of the flange 32 with one or both of the sealing thrust washers 34, 35, thirdly by the '0' ring seal 29, and fourthly, in the case where ambient pressure is significantly greater than process gas pressure, by the sealing action of the cover 37 on the body 2. Although neither of the seals involving in one case washers 34, 35 and in the other case seal 29, being seals between relatively rotatable parts, can individually be considered to be as effective as the seal provided by bellows 19, in aggregate their sealing function is effective to that extent, so that, should the bellows 19 fail, 100% integrity is maintained. Valves according to the invention have one application (the particular application hereinbefore referred to) as process gas valves employed in the pipework involved in centrifuge cascades for the separation of the U235 and U23, isotopes of uranium, the process gas being uranium hexafluoride. WHAT WE CLAIM IS:

1. A process gas valve having a valve body, a valve closure member longitudinally movable in the valve body, and a bellows seal between the valve closure member and the valve body for preventing leakage between the interior and exterior of the valve, characterised by means for sealing said bellows seal at one end to the longitudinally movable valve closure member, means for sealing the other end of said bellows seal to an intermediate member, means for mounting and sealing said intermediate member fixedly in said valve body, a valve operating member having a screw-threaded blind bore, a screwthreaded stem of the valve closure member extending through said intermediate member with clearance and engaging said bore, the valve operating member being mounted for rotation in said intermediate member but being restrained against axial movement relative thereto, and means for sealing between said intermediate member and daid valve operating member.

2. A valve according to claim 1, characterised in that said means for mounting and sealing said intermediate member fixedly in said valve body includes at least two seals in tandem.

3. A valve according to claim 1, characterised in that said means for sealing between said intermediate member and said valve operating member is constituted by at least two seals in tandem.

4. A valve according to claim 3, characterised in that the innermost seal is constituted by, in the closed position of the valve, the engagement of the valve closure member with its seat in the valve body, and in the valve open position, the engagement of a sealing surface of the valve closure member with a seat on said intermediate member.

5. A valve according to claim 3, characterised in that a non-innermost seal is constituted by a pair of sealing thrust washers interposed between each plane face of a flange of the valve operating member and registering annular shoulders provided by an annular recess in said intermediate member.

6. A valve according to claim 5, characterised in that an additional, outer seal is constituted by an '0' ring seal mounted in the intermediate member and contacting an external cylindrical part of the valve operating member.

7. A valve according to claim 5, characterised in that an additional, outermost seal is constituted by engagement with the valve body of a cover for the operating end of the valve.

8. A process gas valve, substantially as hereinbefore described with reference to the drawing accompanying the Provisional Specification.