CA1116977A

CA1116977A - Pressure vessel

Info

Publication number: CA1116977A
Application number: CA000326792A
Authority: CA
Inventors: Jacques H. Mercier
Original assignee: NORMAND TRUST
Current assignee: NORMAND TRUST
Priority date: 1978-06-28
Filing date: 1979-05-02
Publication date: 1982-01-26
Also published as: IT7923894A0; NL7904345A; CH630145A5; PL216615A1; DE2923657A1; FR2429915B1; DD144586A5; JPS556083A; SE7905640L; BR7903922A; GB2024329B; IT1121959B; AU4822479A; AU519635B2; DE2923657C2; JPS6213202U; FR2429915A1; GB2024329A

Abstract

6??-548 Accumulator Device or the Like ABSTRACT OF THE DISCLOSURE

This invention relates to an accumulator device or the like comprising a pressure vessel having a cylindrical interior with a port at each end and an elastomeric separator or bladder interposed between the ports. An annular supporting member engages an enlarged bead at the open mouth portion of the bladder. The device is characterized by the supporting member which is in a non-critical manner bonded to the inner walls of the casing, cooperating with the bead by virtue of the special shapes thereof to coordinate with the bead and with the casing in such manner that the bead is deformed in the mounted position thereof so as to define a fluid-tight seal between the supporting member and casing. The spacing of the terminal end of the supporting member remote from the portion connected to the casing is spaced from the inner wall of the casing a radial distance substantially equal to or greater than the wall thickness of the bladder. The maximum radial thickness of the bead is between about two and one-half and three times the thickness of the wall of the bladder.

Description

BACKGROUND OF THE INVENTION

The present invention relates to pressure vessels, and more particularly to pressure vessels of the type com-prising a rigid casing having axially aligned ports at its respective ends and a deformable separator dividing the vessel into two variable volume fluid chambers communicat-ing respectively wlth the ports. The deformable separator i8 in the form of a bladder having a closed lower end and a mouth with a peripheral bead. The bladder is attached at its mouth to an annular supporting member disposed inwardly of and fixed to the casing.

TRE PRIOR ART

Known armular supporting members are of the thick or thin-walled construction. In the first type of annular supporting member a groove is cut deep in the thick-walled annular supporting member and accommodates the bead of the bladder therein. In the second type of construction the bead is actually molded on the end of the thin-walled annular supporting member. Examples of the first type of construc-tion in United States Patent No. 2,394,401 (Overbeke) and 3,168,907 (Mercier, et al.), and of the second type in my United States Patents Nos. 3,946,759 and 3,830,259.

~, It has also been proposed to clamp the bladder between a supporting member of thin-walled construction and the casing, ~ust below the bead on the bladder which is then received in an annular groove in a hook-like portion of the supporting member as disclosed in United States Patent No. 3,948,287 (Sugimura, et al.). Such clamping of the bead occurs precisely where traction and flexure forces on the bladder are greatest and is a cause of considerable fatigue shortening the service life of the bladder.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a pressure vessel having an annular supporting member of the thin-walled type having a specially formed hook-lik~ portion coacting with a complemental bead on the deformable separator which combineto insure trouble-free securement of the deformable separator with consequent long service life. A further object of the invention is the provision of a pressure vessel which can be mass produced at low costs.

The present invention provides for a pressure vessel comprising a casing of rigid material having two closed ends with axially aligned ports and an internal vertical planar wall, a deformable separator disposed inside said casing be-tween said ports to define variable volume fluid chambers on either side of said separator, said separator having a mouth and an annular ~ead therealong, an annular separator supporting member fixed to the internal vertical planar wall of said casing, said supporting member being of sheet material construction sub-stantially thinner than said casing and including a substantially cylindrical portion adapted to bear against the internal wall of said casing, a smoothly curved hooklike portion defining a radially outwardly opening groove for accommodating said bead of said separator, a connecting zone between said substantially cylindrical portion and said hooklike portion defining a wedge-shaped space with said internal wall, said bead being clampingly disposed within said wedge shaped space in compressed condition to define a fluid-tight seal between said supporting member and said casing; and an end portion at the end of said hooklike portion remote from said connecting zone being radially spaced from said internal wall of said casing a distance equal to or greater than the undeformed wall thickness of said separator so that the portion of said separator between said end portion and said internal wall of said casing is not compressed by said end portion, said bead including a thickened zone facing said internal wall of said casing such that in undeformed condition it is of greater radial extent than the radial depth of said groove measured to theînternal wall of said casing, and said radial depth of said groove having portions which are at least two and one-half times the distance between said end portion and said internal wall of said casing, said bead having a deep cut-a-away zone facing said end portion of said separator suppor-ting member so that said deep cut-away zone compensates for said thickened zone and allows expansion therein of said bead during compression of said thickened zone so as to prevent pinching of said separator in the course of mounting it in said casing.

7~

Owing to this construction the deformable separator is free of substantial compression between the rounded end of the supporting member and the casing, that is, where traction and flexure forces are exerted in operation. The deformable separator is thus protected from fatigue which would otherwise be detrimental to its secure-ment and service life. The rounded end of the supporting member, which i5 preferably rolled, also protects the deformable separator from tearing in the course of de-formation and flexure.

The hooklike portion accommodates the bead and owing to its considerable depth permits a thickened bead to be used. During assembly the bead is compressed and bead material is squeezed upwardly and flows into the wedge-shaped space between the connecting zone and the casing, thereby compressing the bead enclosed in the hooklike portion so as to provide optimal securement.

The wedge-shaped space is sufficiently dimensioned so that bead material may be amply accommodated without a risk of shearing the deformable separator during assembly.

37 ~

Another feature or this arrangement i~ the pro~i~lon Or a fluidtight seal between the annular æupporting means and the casing to hermetically lsolate the flula chamber~ from each other so that the mean~ for securing the annular supportlng member to the casing need not ln~ure fluid tightne~æ.
Preferably the securing means ~or the supporting member are bonding means, e.g. spot welds, a continuous weld or adhesive.
It is not necessary to insure systematlc inspection of the contlnuity Or the welds or adhesive since the sealing function i8 perrormed by c4~pression of the bead in the wedge shaped space the securing mean~ functioning merely to prevent axial shifting Or the supporting member.
According to other features the hookllke portion has slightly incllned rlank~ or opposed slope, a ~irst inclined flank ad~oinlng the rounded end belng substantially perpendi-cular to the centerline o~ the wall of the separator in lts mean posltlon between lts rest posltion and its distended position agaln~t the internal wall or the casing. The second lnclined flank or the hookl~ne portion ad~oining the substan-tlally cyllndrical portlon of the supporting member make~ an angle with respect to a plane perpendicular to the axi~ Or the vessel which i~ greater than the angle which the ~irst inclined rlank makes with its plane~
Thus, preferably, the ~irst lnclined flank of the hooklike portlon iB of flattened fru~toconical configuratlon.
According to still another preferred feature o~ the present invention the radial extent o~ the first n ank is greater than the distance between the radially outermost surface on the rolled portion and the internal wall o~ the casing, whereby the fir3t flank constltutes a retaining shoulder for the bead.
Owing to thls arrangement an excellent securement of the separator is achleved sinre the first lncllned flank pro~ideR a retaining shoulder substantlally perpendicular to the ~ine along whlch traction forces are exerted on the separator and in addltlon it asslsts the squeezing or flow of excess bead material towar~s the wedge-shaped space durlng mountlng, thanks to the more appreclable slope of the second lnclined flank of the hooklike portion. In other words, the rirst lncllned flank forms a bead retalnlng shoulder and the second lnclined flank forms a slldeway for orlenting the movement of excesR bead material towards the wedge-shaped space.
Embodlments of pressure vessels according to the ln-Yention are descrlbed hereinafter, by way o~ example, with reierence to the accompanying drawings.

Brie~ Descri~tlon or the Drawings Flgure 1 18 a longitudinal sectional view of a pressure vessel embodylng the present inventlon ;
Figure 2 15 a fragmentary view on an enlarged scale showlng the securement o~ the separator bead to the supportlng member in the mounted pos~tlon ;
Figures3-6 show the several successive stages of the mounting Or the separator in the caslng ;
Figures 7 and 8 show modi~led embodlments in whlch the bonding means are spot welds and adhesive, respectively, and Figure 9 ls a fragmentary Ylew of a modified embodiment in which the rolled end of the annular supportlng member 18 a toroidal member dlstinct rrom the rest o~ the æupportlng member.

Detailed Descriptlon Or the Preferred_Embodiment Reierence will ~lrst be had to Flgures 1-6 wh~ch il-lustrate by way of nonlimiting e~ample, an oil-gas type pressure ves~el. m e pressure ~essel comprises a casing 10 of rigid material, ~uch as steel, capable of withstanding the pres3ures to which the pressure vessel ~ill be sub~ected ln use~
The caslng 10 comprlses a gererally cylindrical body 11 wlth closed ends 12 and 13. The closed end 12 has a fluid port 14, for example an oil port, adapted to be connected to a fluid coupler (not shown). The other closed end 13 has a fluid port 15 for example a gas port, in whlch ls mounted a gas charglng valve 16. Port~ 14 and 15 are ln axial allgnment.
~ore speci~icallg, the casing 10 comprlses flrst and second opposed shell member~ lOA and lOB. The first shell member~lnclu~es the closed end 12 and a long section llA of the cyllndrlcal body 11. The sectlon llA ~as a sharp annular beveled llp 27. The second shell member lOB lncludes the closed end 13 and a short sectlon llB of the cyllndrical body 11. The section llB ha~ a sharp annular beveled lip 28 sllghtly spaced from the be~eled llp 27 of the first section llA.
m e two shell members lOA and lOB are ~xed to each other by an annular weld ~9 whlch extend~ inside the annular V-shape~ notch deflned by the be~eled llps 27 and 28 Or sections llA and llB.
A deformable separator 17 is p~sitioned inside caslng 10~ the separator 17 being an elongate bladder of rubber or similar material havlng comparable characteristics. The bladder or separator 17 ls interposed between the ports 14 and 15 to define two varlable volume fluid chambers, l.e. a liquid chamber l9 and a ga8 cha~ber 20.
The deformable bladder or separator 17 has at itB
lower end 21 a valve member 22 whlch cooperates with a valve seat 23 deflned around l~quid port 14. The val~e member 22 preierably compri3es a cast steel or aluminlum dlsc at the lower end ~l of the bladder or separator 17.
The bladder or separator 17 has a generally conlcal sldewall 24 ilaring from the lower end 21 to a mouth 25 along whlch i8 an annular bead. m e outer diameter of the mouth 25 is substantlally equal to the internal dlameter of the caslng 10. The bead 25 ls attached to an annular supporting member 26 Or thin-walled or sheet material con truction, e,g. steel or s~nthetic pl~stic material, mounted inwardly ad~acent the cylindrical body ll. In the embodiment or Figures 1-6 the thicknese of the supporting member 26 is less than hali the thicknes~ or the caslng ll and may, ~or example, be one quarter or one iiith or this thlckness.
Such a pressure vessel operates in a manner known per se, as follows:
The port 14 i~ connected to a hydraul~c unl~ and gas e.g. nitrogen, i8 supplied under pressure through valve 16 into chamber 20 untll the deiormable separator becomes dis-tended and bears again~t the internal wall oi casing 10.

A stop cock (not shown) ls interposed between port 14 and the hydraulic unit and when it is in open position the pressurized liquid, e.g~ oil or water admitted through port 14 intO chamber 19 acts again~t separ~tor 17 to compress the gas ln chamber 20 causing the Yolume in chamber 20 to be reduced and llquid to enter chamber 19. m e pressure vessel 1~ then in operative condition. Oil contained in chamber 19 is, if necessary, con-Yeyed to the hydraulic unlt by means of the pressu~ in the gas chamber 20 actlng against the separator. When this happens, the chamber 19 empties and lf lt ls completely emptied the val~e member 22 beare æealingly agalnst valve seat 23 to close off port 14.
The annular supporting member 26 i8 ~ixed, for in-~tance~ by a weld 30 along the inner wall of shell member lOA, sllghtly axially spaced from beveled lip 27.
The annular ~upportlng member 26 Or sheet material has a ~ubstantially cylindrlcal portlon 31 the free end of which i8 welded at 30, followed by a rillet or radiused connecting zone 32 deflnlng a wedge-shaped annular space C with the inner wall of the casing 11, then a hookllke p~rt1on 33 and flnally a rounded or preferably rolled end portion 34.
AR indicated above the annular supporting member 26 which is of relat~vely rlgid material, such as steel or syn-thetic plastic material, ls slightly flexible owing to its unstiffened thin-walled construction along its cylindrical portion 31, whereas its rolled portions 33 and 34 which are 7 ~

profiled are practically rigid. Alternatively, the cyllndrical part 31 may be ~llghtly ~rustoconlcal before mountlng suppor-tlng member 26 incasing 10 50 as to e~ert a slight prestress-ing action at the time of as~embly.
The hookllke portion 33 comprises two slightly incllned flanks o~ opposed slope, and flattened frustoconlcal con~igura-tion, namely, a first lncllned M ank 35 adjoining rolled end 34 and a second lnclined flank 36 ad~oining connecting zone 32.
The lncllned flank 35 makes an angle A with a plane perpendic-ular t~ the axl8 Or the caslng and the second inclined flank 36 makes an angle B, greater than angle A, with such plane.
Preferably angle B is about t~ice aæ large a~ angle Ao Further~ inclined flank 35 18 disposea perpendlcular to the mean center llne posltlon D of the sldewall Or the ~eparator between the rest po81tlon (shown in phanto~ llnes ln Figure 2) and a dlstended po#ltlon ln which the separator bears againet the internal wall Or the casing 10.
Accordingly, the incllned flank 35 i8~ on the average, dlsposed perpendicular to the llne along which the separator i~ ten3ioned in operatlon and acts as a retalnlng shoulder ~or bead 25, The other incllned flank 26 permlts sllding of the bead material to orlent lts deformatlon lnto the wedge-space space for accommodatlng the exce~s compressed bead m~terial.
The dlstance E between the rolled end portlon 34 of the supporting member 26 and the lnternal wall of the cylln-drlcal body 11 may be clearly viewed ln Figure 2 of the draw-ingB. Thl6 dlstance ~ i8 substantially equal to the t thickness o~ the bladder or separator 17 in it6 rest posltlon so as to avoid any substantlal clamping or pinchlng ffl the separator 17 at this point. me depth F of the hooklike portion 33 of the supporting member as measured from the internal wall of the cylindrical body 11 ls selected to be equal to or greater than two and one halr times the dlstance E. Preferably the distance F ls between two and a half and three times the dl~tance E.
me axlal height G of the hooklike portion 33 as measured from the radlal outer limlt of the rolled edge 34 parallel to internal wall 11 i8 equal to or greaterthan the dlfferencebet~een dlstances F and E.
Wlth further reference to Flgure 2, ~he annular supporting member 18 shapea and dlmen~ioned to comply with certain relationshlps to achie~e maxlmum holding of the bead and thereby the entire separator.
In order to measure the varlous dimenslons or ~he arrangement a Eieries Or llnes are drawn parallel to the mean po~itlon D of the center llne Or the ~eparator sidewall.
These lines Ll, L2, L3, L4 and Ls are drawn a~ follows. 1ine L
is slmply the outer sur~ace of the separator 17 in its mean position o~ the separator correspondlng to the mean positlon D of the center line. 12 is drawn tangent to ~he radial outermost surface on the rolled lower portlon 34. L3 i8 drawn parallel to center llne D at the Junctlon between the beginnlng of the rolled lower end 34 and the lower flank 35 of the hooXlike portion. L4 ls drawn parallel to the center llne D at the ~unction between the start of the 'ower flank 35 and the arcuate hooklike portlon 33. Flnally, L5 i8 drawn parallel to the center line D from the radial innermost sur-face of the hooklike portion 33. The distance between the lines Ll and ~ i~ d~, the distance between L2 and ~ i8 d2, the dlstance between L3 and L4 is d3, and the distance between L4 and ~ 18 d4.
Accordlng to preferred embodimen~ of the invention the distances dl, d2, d3 and d4 are chosen 80 that the follow-relations a~e satlsfled :
~1) d2 ~ d

(2) d3 > d

(3) d4 ~ dl Re~erence i6 next made to Figure 3 where the be~d 25 i8 illustrated in solid lines in itæ undeformed condition, the internal wall of the cyllndrical body of the prssure vesgel and the bead supporting member 26 being shown ln phan-tom lines. It i8 seen that the contour of the bead 25 substan-tlally mates with the inclined flanks 35 and 36 Or the hooklike part 26 and has an extra thick zone S facing the inner wall 11 of the pres~ure vessel and a deep cut portion R facing t~
rolled lower end 34 of the supporting member. The additional depth of deep cut portion R is substantially equal to the extra thlckness of Zone S.

When assembling the pressure vessel, first, the bead 25 ls inserted in the correspondingly shaped hooklike port~on.
Then the ~ubassembly ~ade up of the supporting member 26 and the bead 25 ~s introduced into the first shell member lOA ~the beveled lip 27 of which is visible.] The engagement of the subassembly past the rolled edge 34 has the combined effect of the extra thick zone S compensating for the deep cut R and squeezing the deformed bead m~terial 25A into the wedge-shaped space C defined between the connec~ng zone 32 and the internal wall of the casing 11 (~ee Figures 2 and 6). ~t should be noted that the fillet or radiused zone 32 facllit~tes the insertion of the cylindrical portion 31 into the Shell member lOA.
This deformation of the extra thick æone S of the : bead 25 produce~ excellent holding of the bead 25 in the ~ hooklike portion of the supporting member without pinching the separator or bladder 17 owing to the deep cut R facing the lower rolled end. Fluidtightness between the chambers 19 and 20 is insured by the wedging of the deformad bead material 25A in the wedge-shaped space C.
It ~ill be appreciated that the flow of the bead material into the free wedge-shaped space is favored by frlction o.~ the casing 11 against the extra thick zone upon assembly.
m e wedge-shaped space C is formed sufficiently large for the bead material which M ows thereinto to be amply accommodated without risking shearing of the separator or bladder by the sharp edge of the beveled lip 27 when the 7Y~

cylindrical portion 31 reaches the same.
To insert the subassembly comprised of the support-ing member 26 and the bead 25 into the shell member 10A a mandrel (not shown) is advantageously utilized. The mandrel bears agiinst the upper end 31~ of the cylindrical portion 31 and abuts against beveled lip 27 o~ the shell member 10A when the right predetermined position is attained, with the upper end 31t longitudinally spaced inwardly from lip 27. When the subassembly 25-26 arrives in this position in the shell member 10A of the casing, the upper end 31~ of the cylindrical portion 31 is then welded to the internal wall of the casing at 30 with a continu-ous weld as shown in Figures 1 and 2, or spot welds (as shown in Figure 7). Then the s~ell member lOB is brought into position on the shell member 10A and welded thereto as at 29.
It will be appreciated that the pressure vessel according to the present invention enables mass production at lower production costs with a considerable choice of casing and supporting member materials whlle insuring the trouble-free securement and long service life o~ the separator. It will be noted that it is not necessary to machine grooves or slots in the casing which are expensive and/or difficult operations specially in synthetic materials and which weaken the casing and thus require overdimensioning the casing thereby increasing their weight and cost.
The slightly inclined first flank 35 of the flattened ~rustoconical configuration which is perpendicular to the mean position of the center line o~ the separator or bladder 17 in the cour~e of operatlon, provides an extremely sturdy securement of the bladder while the ~luidtightness i~
faultlessly insured bet~een chamber~ l9 and 20 by the en-gagement oP the deformed bead material 25A wedged between th~ connecting ~one 32 and the inner wall o~ the casing 11.
It 18 thus possible to avoid having to insure fluidtightness by the Junction which secures the supporting member 26to the casing. m e devlce of the in~entlon thus makes it possible to spot weld the shell members together at spaced positions, an operation which would not otherwise be permisslble.
According to a modifled embodiment shown in Figure 8, which ~s generally similar to the prevlous embodiment, the upper end of the cylindrical portion 31 of the supporting member comprises an angled rim 37 whlch ~orms an annular recess 38 ~or a weld or a bead of adhesive 30. It should be noted that the supporting member may, in the latter case, be rormed Or synthetic material~ and there~ore admlts o~ the use of a caslng ll o~ rein~orced plastlc material, Such a construction i8 especlally interesting when the liquid to be used 18 hlghly corrosive wlth respect to metals, when a coating is not deslr-able on such a metal or where extremely high pressures are not to be encountered.
In case the bonding means i5 an adhesive, the recess 38 makes it possible to apply the ~ame under excellent conditions for drying and hardening, Such a recess or gutter 38 help avoid dripping Or not yet dried adhesive into the bladder or separator~

~ n F~gure 8 the connecting zone 32' i8 frusto-conical shape rather than radiused or filleted as in the previous embodiments.
In Figure 9 instead of the rolled end portion of the annular supporting member 40 belng fo~med in one piece with the re~t of the supporting member 40 it is distinct therefrom. The rolled lower end of the supporting member - comprises a toroidal member 41 of preferably circular cross section formed of yieldable material which is harder than the bead ~ material. Accordlngly, when assembled, the bead material tends to deform around the upper surface of the toroidal member 41 as illustrated. Thus, unlike the previous embodiments wherein the rolled end portlon depends from the ad~oining lower or flrst flank, the toroidal member extends upwardly relative to the surface of the long flank 42. The toroidal member therefore tends to reinforce the holding capaci-ty of the bead owlng to its convex upper surface compared to prior art devices in which the surface of inclined portion are generally concave, which concavity weakens the hold the supporting member might otherwise provide. Finally, as illustrated, lt is preferred to form the toroidal member 41 slightly offset on the free outer edge of the first flank 42 to prevent undue deformation of the bead for a given radius of the rolled portion.
It will be recognized that variations of the present pressure vessel may occur to those skilled in the art in light of the teachings hereofO Accordingly, the invention is to be broadly construed wi~hin the scope of the accompanying claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pressure vessel comprising:
(a) a casing of rigid material having two closed ends with axially aligned ports and an internal vertical planar wall;
(b) a deformable separator disposed inside said casing between said ports to define variable volume fluid chambers on either side of said separator, said separator having a mouth and an annular bead therealong;
(c) an annular separator supporting member fixed to the internal vertical planar wall of said casing, said supporting member being of sheet material construction sub-stantially thinner than said casing and including:
(i) a substantially cylindrical portion adapted to bear against the internal wall of said casing;
(ii) a smoothly curved hooklike portion defining a radially outwardly opening groove for accommodating said bead of said separator;
(iii) a connecting zone between said substantially cylindrical portion and said hooklike portion defining a wedge-shaped space with said internal wall, said bead being clampingly disposed within said wedge shaped space in compressed condition to define a fluid-tight seal between said supporting member and said casing; and (iv) an end portion at the end of said hooklike portion remote from said connecting zone being radially spaced from said internal wall of said casing a distance equal to or greater than the undeformed wall thickness of said separator so that the portion of said separator between said end portion and said internal wall of said casing is not compressed by said end portion;
(d) said bead including a thickened zone facing said internal wall of said casing such that in undeformed condition it is of greater radial extent than the radial depth of said groove measured to the internal wall of said casing, and said radial depth of said groove having portions which are at least two and one half times the distance between said end portion and said internal wall of said casing, said bead having a deep cut-away zone facing said end portion of said separator supporting member so that said deep cut-away zone compen-sates for said thickened zone and allows expansion therein of said bead during compression of said thickened zone so as to prevent pinching of said separator in the course of mounting it in said casing.

2. A pressure vessel according to claim 1 wherein said end portion of said annular supporting member is rounded.

3. A pressure vessel according to claim 1 wherein said end portion of said supporting member is rolled.

4. A pressure vessel according to claim 1 wherein said end portion is a toroidal member which is distinct from and formed on the radially outer end of said hooklike portion.

5. A pressure vessel according to claim 4 wherein the toroidal member is formed of yieldable material harder than that of the separator, and wherein said toroidal member is dis-posed eccentrically of the end of the hooklike portion.

6. A pressure vessel according to claim 1 wherein said groove has generally radially extending flanks slightly inclined relative to each other.

7. A pressure vessel according to claim 6 wherein a first said flank adjoins said end portion and is substantially per-pendicular to the mean position of the center line of the sidewall of said separator between its rest position and its distended position bearing against the internal wall of said casing.

8. A pressure vessel according to claim 7 wherein said first flank is of flattened frustoconical configuration.

9. A pressure vessel according to claim 7 wherein the distance d1 between said end portion and the internal wall of said casing is less than the length d3 of said first flank which defines a retaining shoulder for said bead, less than or equal to the length d4 of said hooklike portion inwardly of said first flank, and greater than the length d2 of said end portion between its radially outermost surface and its junction with said first flank.

10. A pressure vessel according to claim 7 wherein a second said flank of said groove adjoins said substantially cylindrical portion of said annular supporting member and makes an angle with a plane perpendicular to the axis of said casing greater than said first flank of said groove makes with its corresponding perpendicular plane.

11. A pressure vessel according to claim 10 wherein said second flank is of flattened frustoconical configuration.

12. A pressure vessel according to claim 10 wherein said second flank makes an angle with a plane perpendicular to the axis of said casing which is at least twice the angle said first flank makes with its plane perpendicular to the axis.

13. A pressure vessel according to claim l wherein the height of said groove measured in line with said end portion of said supporting member is at least equal to the difference between the radial depth of said groove and the distance between said end portion and said internal wall of said casing.