Note: Descriptions are shown in the official language in which they were submitted.
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' HIG~ PR~SSU~E SHELL
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BACKGROUND OF THE I~VE~TION
The use-o r membranes to e~'ec- separation of ~as/gas,
liquid/li~uid, and liquid/solid mixtures and solutions has
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achieved general industrial applicability by various methods,
among them being ultrafiltration, hyperfiltration, reverse osmosis,
dialysis. In general, membrane elements associate~ with these
¦iprocesses are c~ntained in vessels, comprisin~ a container having
various inlet and outlét ports and an assembly of membranes ~Jithin
sai~ container, the entlre assembly being-referred to as a module.
The internal configurz-ions are so arranged as to ~ermi. the intro-
duction of a feed stream with or without-pressure on the upstream -
face of ~he membranes, means for collecting permeate which pzsses
though the membranes and emerges on their dot~7nstream faces, and
means for ~.eeping feed and permeate materials rom commingling~
In the field OI reverse osmosis therefore and in other
related hiyh-pressure fluid dynamic operations, there is the need
for low cost, high streng-h shells capable of sustaining internal
operating pressures in the range of several hundred to a thousand
, or more psi. These shells are often 2", 4", 8", or even larger
in diameter and may run in length from a foot or two up to twenty
feet or more. In the reverse osmosis situation, they are the
housing in which the membrane separatory elements are contained.
Initially, shells of the latter sort were fabricated
of bulk metal. More recently these shells have been fabricate~
of fiberglass reinforced plastic, generally epoxy resin.~ For the
mosL part, such shells have been fzbricated by conventional fila-
ment winding, although ordinary biaxial ~raiding has ~een utilize~
for the fabrication of the fibrous reinforcement of the shëll.
A difficulty with these con~igurations has been the
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methods of end closure, seallng, and making connections~for plpe
, fittings. Various configurations have been utilized involving
'grooves machined into either the internal surface or the external
surface of the shell, which afford anchorage sites on the shell
l for sna~ rings and the like. Alternatively, sleeves which fit
snugly over the outside diameter of the shell have been bonded to
; their external surfaces with glue in the fashion of a coupling in
j order to provide a means for end connection. In another alter-
,native, overlap layers of fibergl2ss windings are applied near ,
the ends of the pressure tubes in order to make a thickness
'capable of being drilled for bolts, or, in other configurations,
bolts or studs have been trapped in-o extra thick encs during
~` filament winding.
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The pressure shell must not only absorb the internal
hydraullc forces in the radial direction, but, if longitudinal
''tie rods are to be avoided, it must also accept axial stresses
. ' imposed on the shell. 'In the conventional designs this lea~s to ~--
, two inherent deficiencies. ~ne has to do with the fact that the
filament-wound'fibers lie at a helix angle to the axial direction
"20 ' of stress, and unless the helix is rather steep, an excessive
'~ amount of winding is required to develop a significant axial
-component capable of ,aking up the longitudinal stress in the
,shell.
~urther considerations relate to the problems of end
closure andend connections. Each of the alternative metho~s for ~ j
creating a closure connection referred to above in the conven-
tional systems relies upon the shear strength of the e~oxy matrix ,
primarily if not entirely. In some instances this calls for an
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excessive amount of shell overhang in the case where machined
grooves are used for snap rings. In other cases, serious
failures have occurred when -the glue line between a bonded
coupling and the shell has weakened.
SUMMARY OF THE INVENTION
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A construction in accordance with the present
invention includes a shell for use in high pressure appli-
cations, including an inner liner, end plugs, and at least
two systems of filaments with a first system parallel to the
longitudinal axis of the liner. Means are provided for
retaining said end plugs by operatively engaging the first
system whereby internal longitudinal pressure forces on the
plugs are substantially resisted by the first filament
system which is parallel to the longitudinal axis of the ..
liner.
More specifically, the invention to be more fully
described is a generally cylindrical pressure-resistant
impervious shell comprising a polymeric ma-trix reinEorced by
at least two distinguishable sys-tems of filaments, one said
system having filamen-t axes lying substantially parallel -to
the longitudinal axis of the cylinder. At least these fila-
ments follow a path which reverses direction at one or bo-th
ends of -the cylinder i.n such a way as to engage a ring-link
retaining member at one or each end of the cylinder. In a
preferred embodirnent -the pressure shell comprlses an imper-
vious polymeric inner liner over which is assembled a compo-
si-te of polymeric resin reinforced by a -triaxial braid having
yarns lying both in left and right hand helices and in a
path parallel to -the axis of -the cylinder. The -triaxial
braid is applied so -that it forms a number of layers and
en-traps a ring between a pair oE braid layers at one end and
between a pair of layers a-t the other, at least one layer
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being common to each such pair.
In other embodiments of our invention the inner
impervious liner may be eliminated and the resin comprising
the composite molded with the filaments so densely as to be
impervious to high pressure fluids.
In still another embodiment, the braid may be of
simple double-helical s-tyle with non-braided yarns laid in
to provide the longitudinal filaments parallel to the cylin-
der axis. At least the laid-in axially parallel yarns make
path reversals at
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'each end of the cylinder and engage retaining rings thereby.
In still another'e~bodimen. the ~ilaments may be part
of tubular woven fabric, where again one set of yarns lies
, ~ p'arallel to the cylinder axis and by reversing direction at each
, end eng2ges retaining rings by entrapping ~he~ be.ween layers of
the tubular fabric.
The principles, of these embodiments are illustrated by
'the drawings.
DESCRIPTION OF THE DRAWI~JGS
10 , Fig. 1 is a schematic longitudinal cross-section draw-
ing of a prior art shell;
,Fig. 2 is a schematic longitudinal cross-section drzw-
ins of the outer reinforcement structure of a shel~ constructed
in accordance wi,h 'he subject invention;
Fig. 3 is a perspective view of a shell constructed in
accordance with the sub~ect invention;
g. 4 is a longitudinal sectional view taken along
the line 4-~ in the direction of ~he,arrows in Fig. 3; and
Fig. S is a segmentary view of the triaxial braiding
;~`' ,'used in the construction of the reinforcement structure of the
shell shown in ~ig. 3.
DESCRIPTIO7~ OF TH~ PREFERRED_E.r~BODI~ENT:
I,, In Fig. 1 a prior art shell for use in high pressure
',fluid operations is shown in schema.ic cross-section for,m in order
~to illustrate difficulties of,end closure and end connection
found to exist in the prior art. The shell of Fis. 1 includes a ,
cylindrical outer wall 10 which can ~e fabricated of fila~ent
wound fiberglass reinforce~ ~poxy ~ateri21, end plates 12 and 14
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maintained in position against the internal pressure'"P" by
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snap -rings 16 2nd 18 which are set in respective cylindrical
grooves 20 and 22 for~ed in the inside surface of'wall 10. "0"-
rings 24 and 26 are shown as typical sealing me2ns.
Broken lines 2~ and 30 illustrate the locus of shear
failure to which t~e shell is susceptible. In the absence of
bulk strength in the wail, which is costly and inconvenient, some
means is requlred to anchor the end plugs in the presence of
longi,udinally directed pressure forces which does not rely upon
~ the shell'wall material to'resist shear.
Figure 2 illustrates ho~ the present invention solves
this problem. I~hat is illustrated by this diagrammatic cross-
-section is the ~rganization of layers of fabric having longi-
tudinal filaments making path reversals around entra~ped rings
at each end. In this illustr2tion one such ring has z diameter
' larger than that OL the shell, and the other is smaller. ~he
reinforcement fabric'is described consisting of triaxial braid,
but it should be understood that other yarn asse~lies may be'
, employed as described above,provided one system of yarns lies
parallel to the cylinder axis and makes reversals arounA entrapped
retaini~g rings. The triaxial braid is, however, our ~referrea
embodiment since it lends itself to facile fabrication steps.
TriaY.lal braiding is knot~n and the term triaxial as
used herein contemplates two sets OL yarns lying in helical paths
' in the sense of a conventional braid, with a third set of yarns
l~ing entirely parallel to the lon~itudinal ~irection of the
' shell. This assemblage of three yarn systems can be achieved
on an essentially conventional braider having the faculty for
feeding a third set of yarns which are not caused to intertwine
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by carriers, but rather feed continuously in the longitudinal
direction. Such a configuration is illustrated in Fig. 5 wherein !
yarns indicated by the numerals 32 and 34 are the respective sets
¦of yarns referred to above as lying in helical paths and the
S numeral 36 indicates the third yarn system intended to lie parallel
to the longitudinal axis of the shell.
In Figs. 3 and 4 a shell constructed in accordance with
'¦this invention is illustrated. The outer structure 38 (or outside
l shell) is formed of plastic matrix reinforced by triaxial braiding
1 and the inner liner 40 is shown for purposes of example only.
The inner liner can be fabricated of suitable non-reactive materi-
als and it is conceivable that in certain applica~ions the inner
shell would not be present but rather the reinforced braiding may
l be made impervious by suitable impregnation.
1 The braiding to provide the outside shell 38 may be
carried out over a mandrel (not shown) having a single selected
l diameter or different diameters for different regions of the tube ¦
¦ length, or alternatively it may be carried out directly onto the
inner liner 40. The liner itsel~ may be uniform in inside di- I
ameter over its length or have selectively varied inside diametersl
(and possibly resulting varied outside diameters) over its length,~
depending upon the specifi.c design.
The invention lends itself to making end closures by
l braiding the yarn systems 32, 34 and 36 to create the outer
~ structure 38, over rings 42 and 44 as is shown schematically in
Fig. 2, or by making other controlled changes in the radial di-
mension at specified intervals.
In Fig. 2 an end plug 46 with O-riny 48 is shown~in
position.
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The important aspect of this invention for the fabrica- ¦
tion of end closures is the utilization of filaments lying paral- ¦
lel to the cylinder axis such as can be achieved in a triaxial
braid so that the longitudinal stress in the shell is taken
primarily in the longitudinally oriented yarns. Accordingly, the
invention readily lends itself to the provision in such a shell
of properly connected end plates or other end fixtures by clamps
or inother attachment ways so that the loadings are transmitted
directly to the yarns under tension without relying upon shear
strength characteristics of composite epoxy or other resin. I
With the present invention, it is possible to provide shells ~ith ¦
lightly bonded braided jackets over impervious inner liners and
thereby achieve systems which will be leakproof and have the neces
l sary tensile requirements to take up hoop stresses, longituainal
stresses, and meet end closure requirements.
