Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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 seaks to provide a bellows-sealed
valve which is provided with additional safeguards against
leakage in the event of bellows seal failure.
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 engaged by a screw-
threaded 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 inter-
mediate member but being restrained against axial movement
relative thereto, and means for sealing between said
intermediate member and said valve operating member.
~ 2 -
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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 inter-
posed 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 'O' 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
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of the valve body.
A constructional example embodying the invention will now
be described with reference to the sole Figure of the accompanying
drawing, which is a side view in medial section.
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 PTFE 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 peaned-over 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. Thè annular clearance between the
shank 17 and the bore 16 of the body 2 provides accommodation
for a hellows 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 'O' ring seal 23 of neoprene
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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 (RTM) 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 h~s 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 'O' ring seal 29 of PTFE 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 blind-ended
screwthreaded bore 31 open at its lower 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
26l 26a to facilitate assembly. ~ealing thrust washers 34, 35
of PTFE 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
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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 tconveniently 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 to be considered its only application), the
valve is intended to be used in large numbers, therefore it is
regarded as expendable after a schedule 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 op~n position of the valve, together with the
bellows 19, provide full sealing integrity. But if the bellows
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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 'O' 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, thridly by the
'O' 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 maintalned.
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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 U238 isotopes
of uranium, the process gas being uranium hexafluoride.
