US2804884A

US2804884A - Accumulator whith diaphragm stabilizer

Info

Publication number: US2804884A
Application number: US450139A
Authority: US
Inventors: Granville S Knox
Original assignee: Hydril LLC
Current assignee: Hydril LLC
Priority date: 1954-08-16
Filing date: 1954-08-16
Publication date: 1957-09-03
Anticipated expiration: 1974-09-03

Description

Sept. 3, 1957 G. s. KNOX ACCUMULATOR WITH DIAPHRAGM STABILIZER 2 Sheets-Sheet 1 Filed Aug. 16, 1954 as GPHIVV/LLE 5. KNO 27 INVENTOR.

8- sum p 3, 1957 e. s. KNOX ACCUMULATOR WITH DIAPHRAGM STABILIZER Filed Aug. 16, 1954 \t -1 V V\ I s 1\ s m, on

2 Sheets-Sheet 2 Gen/vv/LLE .9. K/vox,

' IN V EN TOR.

BY Bm '5 42-7-01? Ks ACCUMULATOR WITH DIAPHRAGM STABILIZER Granville S. Knox, Glendale, Calif., assignor to Hydril Company, Los Angeles, Calif, a corporation of Ohio Application August 16, 1954, Serial No. 450,139

14 Claims. (Cl. 138-30) This invention has to do generally with accumulators or pulsation dampeners and is more particularly concerned with such devices wherein diaphragm stabilizing means are included, as well as to the stabilizing means, per se.

The invention is particularly well adapted to handle the severe service requirements of and to withstand the severe conditions encountered in pumping mud laden fluid during well drilling operations, and therefore I have illustrated and will describe an embodiment especially suited to that use, though this is not to be construed as limitative.

In the above environment, dampeners are installed in output lines of reciprocating-plunger, mud or slush pumps, to smooth out pressure peaks. The pre-charged surge chamber effectively eliminates surging and water hammer in the rotary hose and mud lines, resulting in longer service life and less maintenance trouble and expense as regards the pumps, the rotary hose, the swivel packing,

etc. all as is well understood in the art.

In my copending application on Accumulator or Pulsation Dampener, Serial No. 327,280, filed December 22, 1952, now Patent No. 2,757,689, August 7, 1956, I have shown, described and claimed a device having, among other features and advantages, superior characteristics as regards capacity and efliciency, as well as avoidance of harmful folding and wrinkling of the diaphragm, in spite of its advantageous length of stroke.

In that application it is pointed out that undue accumulation of sediment in the body chamber is prevented by the sweeping efiect of the diaphragm when the diaphragm is forced downwardly by gas pressure after the pumps have shut down. It is also set forth that certain parts of the device are so shaped and relatively located that sediment entering the chamber is evenly distributed to the extent that there are no harmful local accumulations of sediment during operation. Thus the accumulator was said to be, in all essence, self-cleaning.

This all proved to be true in actual practise except when certain types of mud laden fluid were encountered. For instance, peculiar results followed when the mudladen fluid tended to gel when it was unagitated. Such was the case when bentonite was one of the constituents of the drilling mud, and I will therefore discuss the problem in that light, without inferring that a stable suspension, such as this, is the only cause of the difficulty or that my remedy applies only when the suspension is stable.

Bentonite is a soft, porous, moisture-absorbing rock,

composed essentially of clayey materials, having the property of thixotropy, that is, of becoming fluid when agitatedthe change being reversible. Thus, when a body of bentonite-laden fluid gathered in the accumulator chamber below the diaphragm, it had zones of differential viscosity; that is, the material in the relatively quiet zone around the periphery of the chamber became gel-like, whereas the material in the central zone or core became fluid due to the agitation caused by the more pronounced movement of the central portion of the diaphragm and to, the jetting effect as the material was discharged from the mud chamber.

a a a As a result, when the pressure of the gas above the diaphragm became effectively predominant upon temporarily shutting down the pumps, the central portion of the diaphragm was plunged down through the low viscosity zone, pulling the upper part of the bladder away from the upper wall of the housing. The elongation of the diaphragm necessary to seat the stopper was thus accomplished by displacement of the upper extent of the bladder rather than by a stretching of the lower extent thereof, as was intended and was normally the case. This left an annular body of gel-like material about the elongated diaphragm. The bladder, being unstretched, had no snap-back characteristics when pressure conditions on opposite sides of the diaphragm were subsequently equalized, and therefore failed to return to a position of equilibrium. As a consequence, its upper extent remained in spaced relation with respect to the upper wall of the housing and an annulus of gel-like material remained around the lower extent. During subsequent cycles of operation additional quantities of the gel-like material gathered between the upper extents of the housing and bladder, further exaggerated the undesirable effect. And, of course, each time the volumetric capacity of the diaphragm bladder was reduced by an ever enlarging annulus of sediment, the contained pressure was increased until it so nearly approached the peak pressure of the pumped fluid that it offered no effective dampening action.

It is therefore a general object of the present invention to provide means whereby the dampener will continue to function with full efliciency in spite of the fact that the fluid being handled is thixotropic, or of any nature which tends to cause it to accumulate in unduly large amount about the bladder. In other words it cares for conditions where the suspension is stable but its viscosity depends on its degree of agitation, or where the suspension is so unstable that the solids settle out with undue rapidity and crust when the fluid is relatively quiescent.

' In general, I accomplish the desired result by attaching the center of a stabilizer, preferably in the form of a relatively stiff rubber disk, to the center of the diaphragm at the gas-chamber side thereof and thus in axial alinement with the stopper at the opposite side of the diaphragm. However, the radially outwardly extending portion of the disk is unattached to the diaphragm, thus being movable with relation to the underlying portion of the diaphragm and permitting said underlying portion to retain its full stretch and snap-back capacities. In other words, the stabilizer has the effect of vertically stiffening the central portion of the diaphragm without affecting the elastic characteristics of the lower extent of the bladder wall. At the same time, the stabilizer is preferably capable of limited, resilient deformation to the extent that it may substantially conform itself to the shape of the engaged portion of the bladder and perform its necessary stiffening function without tending to overstress or puncture the bladder. The stabilizer thus creates an enlarged central area which is axially relatively stiff without impairing other desirable characteristics.

If the diaphragm is working in the lower half of the housing during a given period, the stabilizer acts to increase the effective area of the diaphragm insofar as agitation is concerned, thus giving an increased-area zone of relative fluidity and reducing the extent of the quiescent zone. There is, accordingly, less material available for the formation of gel, thus reducing the hazards otherwise resulting from such formation. On the other hand, such gel as may form beneath the diaphragm (and this also applies where the diaphragm may be working in the upper half of the housing where, under certain circumstances,

the stabilizer adds nothing to the agitating effect) is, in large part, pushed out of the chamber bythe larger-diameter, stiffened portion of the diaphragm, thus reducing the thickness of thegel-annulus below the danger. point, the upper wall of the bladder continuing to hug to the complementary wall of the housing and the lower wall of the bladder being forcedto-stretch as the stopper-hpproachesand-reachesitssea-t. A

The stabilizer is r also helpfulcven though 'the liquid being handled is-entirelyfr'ee of sediment. rForinstance, 1t irons out the -wrinkles-andfolds ofithe diaphragm as they start to form when the diaphragm passes through a median zone, all aswill beexplained.

.-I willdescribe the'invention as-aapplied-to a. pulsation dampener corresponding: to the showing of said. copendi-ngapplication, with which it isrpeculiarlywell-adapted to function, but this is notwto be 'considered as -limitative Ion thebroader aspects of theinvention. p

Other objects and features"of novelty viillbecome'apparent from the following' detailed descriptionfrefereme being had to the accompanying drawings,in which:

Fig. l is a side-elevation of the dampener;

Fig. 2 is atop plan view of-FigJ1 partly'in brokenaway section;

1 Fig. Sis an enlarged section on line 33 of Fig. 2;

Figs. 4 and 5 are fragmentary views sh'owing'the'behavior of the diaphragm under certain. operating conditions.

The body shell or housing is made up of main section 11, cap section 12, and bottom section 13, theportions of the housing above and belowthe central axial plane A being considered, respectively, as upper and lower shell-

walls

14 and 15. The upper end of section 11 has a relatively large-diameter central mouth 16 which receives the cylindrical plug portion 17 of section 12, while the flange portion 18 of section 12 is bolted'to section 11 at 19. The peripheral face 20 of plug portion-17'is annularly spaced from the defining wall '21 of mouth 16.

to provide a downwardly opening, annular groove 22 which, as well as counterbore 23, serve to receiveand anchor portions of the diaphragm or baldder, as will'appear later.

The lower end of section 11 has a relatively smalldiameter central mouth 24 adapted to receive the cylindrtcal plug portion '25 of bottom section 13, the flange portion 26 of section 13 being bolted-tosectio'n 11-at27. The joint betweensections 11 and 13 is packed-oif by compressed sealing -ring 28. Flange 26 hasthreaded holes 29 to receivebolts 30 (Fig. 1) whereby the :flange 31 of fitting 32 may be fastened to the dampener, this fitting being connected by pipe 32' to theoutput line (not shown) of a pump or the like. The pipecommunicates with the central flow passage 33 extending through bottom section 13.

Walls 14, 1S define a chamber C which has the generalshape characteristics of an oblate spheroid'with its polar or shorter axis B extending vertically, it being understood that the words vertical and horizontal are used merely for the purpose of orientation of parts and' not in their limited sense. Axial plane A may--thus be considered as the equatorial axial plane of chamber C, since the line representing that plane also represents the longer axis ofthe generating ellipse.

The lower portion of the defining wall of-chamber C is preferably slightly modified so that the curved defining wall 34 merges smoothly into a conical surface or zone 34' immediately surrounding'the orifice 35 of passage 33, the conical surface smoothly and with stream lines merging into the defining wall of the passage, which latter is in the'nature of a venturi, with the venturi streamlin restriction 36 at a point near said orifice.

The diaphragm 37 is in the 'nature of a bladder made.

of natural or synthetic rubber and is. pre-formed, as by molding, so, when itis in equilibrium, it has the shape shown in solid lines (position D) 'in Fig. 3. The neck 4 housing 10, but also packing ofi the joint between

sections

11 and 12.

When in position D (that is, when the diaphragm is in equilibrium and thus in the shape it inherently assumes when detached from the housing) its upper portion 41 has an arcuate extent 42 which is complementary to and engages upper shell wall 14. Arcuate portion 42 terminates at 45, lying approximately inplane A, and is conextent '46 which merges, by way of curved extent 47,into

an uppermost, substantially horizontal, but preferably slightly crowned, central extent 48. Embedded in this central extent is a downwardly pointing, conical valve stopper49 which is'rigid in nature and is keyedto the rubber diaphragm at 50. Aswill later appear,'the stopper provides anchoring means: for the stabilizer, to be described.

The axes of stopper 49 and pa'ssa'ge 33 are coincident with polar axis B. The rubber making up the diaphragm is c ontinued integrally across the lower conical surface 51 of stopper49 to provide a rubber facing'52 to seat on conicalface 34' around orifice 35 when the bladder is in fully distended condition, as represented by'the dotdash position F, thus to close off passage 33 and prevent extrusion of the bladder into said passage.

Opening through cap section 12 and into the bladder, is a fluid flow passage 53, into which a valved fitting 54 is set. Gas such as compressed air or compressed nitrogen is introduced through fitting 54 to provide the 'pulsation absorbing or dampening medium when surges occur in the fluid admitted through passage 33 to chamber-C below the bladder. A gage '55 is in communication through passage 56 with the bladder interior, whereby the gas pressure within the bladder may be ascertained. Preferably, a guard 57 is bolted tocap section'1'2 to'prot'ect fitting 54 and gage '55, the guard having agage-sighting o'pening58. v

Stopper 49 is centrally boredand threaded at '65 to take bolt-66. This bolt, in conjunctionwith flanged, cupshaped retainer"68,holds the -'stabilizer, generally indicated at 69, to diaphragm'37. The bottom 70 '(Fig. '4) of the cup-portion 71 of retainer 68 engages the upper end 72 of'stopper49, while flange 73 is'vertically spaced above and'substantially parallel to central crown '48 of diaphragm 37.

Stabilizer 69 ispre-formed as a flat disk of rubber, natural or synthetic, having greateraxialstifiness than does the rubber of the diaphragm, and, preferably is somewhat thicker than is the "wall of the diaphragm. For 'instance, it has been found satisfactory, where the diaphragm has a hardness of from 50 to 55 on the durometer A scale, to provide a stabilizer having a hardness'offrom 72 to 85 on that same scale, though theseparticular ranges are not to be considered as limitative. Also as illustrative of satisfactory relationships, the thickness of the stabilizer may be in the order of /2" where the thickness of the diaphragm is in the order of Stabilizer '69 is'centrally apertured at 74 to receive cup 71, whereby the stabilizer is held centered with the 'retainerand hence with the diaphragm, and its inner, annular portion75 is held down to-crown=48 by'fiange '73, said portion 75 being slightly flexed to conform to said crown. The outer, annular portion 76 extends substantially horizontally when the diaphragm is ine quilibrium, there thus being developed an angle of about 30 between said portion and :the conical extent '46,-'though-this angle is not critical and, in fact, may be absent where'it is desired However, it is important that portion 76 be unattached to diaphragm wall 46; that is, portion 76 and wall 46 are to be capable of such relative movement that the stabilizer in no way diminishes the stretchability of wall 46. On the other hand, not only do the inner annular portion 75 of the stabilizer and the retainer flange 73 increase the axial rigidity of central portion 48 of the diaphragm, but also the outer annular portion 76 of the stabilizer axially stitfens or reinforces wall 46 when the diaphragm is moved in a manner to engage that wall.

While the illustrated relative diameters of the diaphragm, at equatorial plane A, and of the stabilizer 69 are not to be considered as limitative, I have found that, for instance, a ratio of about 11 to 9, is especially well adapted to the purpose, this giving a desirable extent of radial extension or overhang of the stabilizer with respect to wall 46. The illustrated ratio (about 5.5 to 9) of the inside diameter of bladder-neck 39 and stabilizer 76, is not at all limitative. However, with this ratio existing it is possible to assemble the relatively large-diameter stabilizer with the diaphragm by bending the stabilizer nearly double and inserting the doubled-up member endwise through the neck. As soon as it is released it will, of course, spring back to its original shape, whereupon the retainer 68 and bolt 66 may be readily applied. Preferably, a shake-proof lock washer 77 is inserted between cup 71 and the underside of the head of bolt 66.

Preferably, though not necessarily, the outer periphery of stabilizer 69 has a double chamfer, as illustrated at 78 to prevent this edge from digging into the diaphragm wall during periods of operation. It may be noted at this point that stabilizer 69 is adapted to flex and therefore approximately conform itself to the upper wall of the bladder in the event the bladder fluid accidentally leaks out and allows the pressure in the lower part of chamber C to drive the diaphragm to its upper limit. In such event, the interposition of the stabilizer between folds of the bladder and between the bladder and the lower end of plug 17 prevents chafing and undue wear on the bladder rubber. I

I will first describe the action of the dampener when the liquid being handled is not of the thixotropic or crusting types spoken of in the introduction. The bladder is preferably precharged so it will be in position F, it having passed through position E in reaching this position F. In going from position D to position B there is a natural tendency for the diaphragm to fold, wrinkle and become locally oif-center-obviously undesirable effects if not held to a minimum. In the illustrated device such effects are sufliciently minimized to insure fully eflicient and longlife operation. Contributing to this end is the fact that the slant height X of the conical extent 46 of bladder base-portion 43 is made to be appreciably less than the radius Y of the bend-annulus 44 when the bladder is in equilibrium (position D). Also contributing is the preformation of the slant angle 60 of the conical extent so,

when the diaphragm is in equilibrium, said angle is less than the angle 61 between plane A and a chord 62 drawn from that plane to the upper end of arcuate extent 42. In the illustrated case, angle 60 is about 30 as against the approximately 54 of angle 61.

Additionally contributing to the above end, is the stabilizer 69, for, as it progressively engages the extent 46, it has the effect of trusting that extent ahead of it through the median zone, more or less ironing out the wrinkles 01 folds as they start to form.

When in position E, the rubber of the diaphragm is unstretched, except slightly at bend 44. In going from position E to position F, the rubber making up wall 46 of the bladder is stretched, the upper part 42 of the bladder continuing to hug housing wall 41. On the other hand, due to the relative rigidity of bend 44, there will be a flattened or return-bend effect 44' which will tend to stand the base portion 43, except for the stopper area,

away from wall 15, thus developing a space 59. Subsequently, an upward surge of fluid through passage 33 overcomes the previously predominant pressure in the bladder and thus unseats valve stopper 49 to admit fluid to chamber C below the bladder. The lower part of the diaphragm then tends to spring back towards positions E and D. When the gas pressure again becomes predominant and re-seats the stopper, some fluid will be trapped in space 59 between return bend 44' and the seated stopper, and this trapped fluid will hold the affected part of the bladder from contacting the shell wall, thus preventing abrasive wear on the bladder. The rubber facing 52 is adapted to make a tight seal whereby the trapping of a relatively small amount of the fluid is assured.

When the liquid being handled is, for instance,'thixotropic, or rapidly crust-forming, the tendency is that spoken of in the introduction. That is, if thixotropic, the suspension tends to gel in the more quiescent annular zones around the housing Wall while the central core of the suspension body becomes very fluid due to the more pronounced movement of the central portion of the diaphragm and to the jetting eiiect as the material is discharged from the mud chamber. The jetting effect is increased by the venturi nature and streamlining of passage 33. These characteristics of passage 33 are helpful in that they so direct the incoming stream of liquid as to distribute sediment evenly over the shell walls, as explained in the aforementioned co-peuding application, but the jetting effect during discharge has its disadvantages where the material is thixotropic, due to its production of a central column of low viscosity-for, if remedial provisions are not made, the stopper and lower end of the diaphragm then would tend to plunge downwardly through the low viscosity column, pulling the upper portion 41 of the bladder away from housing wall 14, ratherthan stretching diaphragm wall 46. would then build up progressively around the vertically elongated, unstretched bladder, and the volumetric capacity of the bladder would thus be progressively diminished until the pressure of the contained gas would so nearly approach the peak pressure of the pumped fluid that it would offer no effective dampening action.

However, stabilizer 69 prevents such disadvantageous diaphragm action, the stabilizer eifect being illustrated in Figs. 4 and 5. In the first place, the stabilizer provides a radially extended, axially reinforced or stiffened central portion of the diaphragm which increases the cross-sectional area of the central core of the mud-laden material which is kept in a low-viscosity fluid condition by reason of agitation due to diaphragm reciprocationthus correspondingly reducing the volume of the surrounding annulus of gel-like material.

In the second place, assume that the gel-like material has gathered beneath the diaphragm when the latter is in the equilibrium position D indicated by dotted lines in Fig. 4. The annulus of such material would appear, in cross section, as made up of the body of 'material M, shown in full lines, plus the then continguous body M indicated in dotted lines. Then, as thedi'aphragm de scends towards E (Fig. 4) the stabilizer comes into engagement with diaphragm wall 46, backing it up and axially stiffening it so as to thrust the gel-like material ahead of it, the surplus being discharged through passageway 33. By the time the'diaphragm reaches position I E, the gel-like material has the approximate cross-sectional shape indicated at M.

In going from position E to position F (Fig. 5) the stabilizer continues to axially back up and stiffen the diaphragm in a manner to sweep the gel-like material ahead of it, the diaphragm wall 46 being stretched in the process, rather than pulling diaphragm wall 42 away from shell wall 14as would be the case if the stabilizer were not present. By the time stopper 49 is fully seated (Fig. 5) V The gel-like material 7. there isieft-only-the relatively small bOdyM -Z of gel-like material between'the diaphragm and the shell, this body being of insuflicient volume to materially affect the volumetric capacity of the bladder and, in fact, having'th e beneficial effect previously spoken of in connection with trapped'fluid in space 59. 7

Thus, at the end of the down stroke of the diaphragm, the bulk of; the gel-like material will have been swept clear of the housing chamber so the volumetric capacity of the bladder will be nearlynormal, and sodiaphragm wall 46 will be in effective tension. Consequently, the entire device is in condition to continue to act effectively as a pulsation dampener in spite of the peculiar nature ofthe material being handled.

While I have shown and described a preferred embodiment of the invention, various changes in design, structure and arrangement may be made without departing from the spirit and scope of the appendedclainis.

I claim:

1. In a device of the character described, a-body shell defining an interior chamber, a rubber diaphragm within the chamber and dividing the chamber into two pressure zones, there being a pair of fluid flow passages through;

the shell, and opening, one each, to said zones, one, at

least, of the passages being coaxial with the diaphragm whereby the central part of the diaphragm moves axially towards and away from said one passage during diaphragm flexure in opposite directions, and a stabilizer mounted on said central portion at the side of the diaphragm remote from said one passage, said stabilizer-having a radially outwardly extending portion overlying but unattached to the diaphragm in the region surrounding said central portion, said stabilizer comprising a member which is flexible and axially resilient.

2. A device as in claim 1, wherein said member-is axially stifler than is the diaphragm.

portion movable axially of the chamber-toward and aw ay from the central portion of the lower shell wall, therebeing a pair of fluid flowpassages opening through the shell, one to the interior of the bladder and the otherto the chamber at a point below the bladder-and-in line with.

the axis thereof, and a stabilizer carried by the bladder and located centrally of the inner face of .the base portion of the bladder, said stabilizer comprising a vertically flex ible and resilient member having greater vertical stiffness than has the flexing wall of the bladder, said stabilizer being centrally fixed to said base portion of tlie bladder and having a radially outwardly extending portion overlying said base portion but unattached thereto.

4. A device as in claim 3, including reinforcement in the central zone of the base portion of the bladder, which central zone acts to close ofi said other passage when the bladder is fully inflated, said extension of the stabilizer exetnding radially outward beyond-the reinforced zone- 5. A device as in claim 3, wherein the stabilizenwhen" in equilibrium, is disk-like in formation.

6. A device as in claim 3, wherein the stabilizer is made;

of rubber.

7. A device as in claim 3; wherein'the stabilizerlismade of rubber which isstitfer than is the rubber of the bladder, and, when in equilibrium, is disk-like in formation.

8. A device as in claim 3, wherein, when the ,upper portion of -the bladder complementarily engages the upper shell wall, the base portion ofthe bladder must be stretched by bladder} inflation in ordertore'ach the lower shell wall, and wherein the stabilizer allows such stretch withput' efle;tive interference.

9, In a device of'thecliaracter described, a body shell having uppr and lower walls defining an'interior chamber ha ingjthe general shape-characteristics of an oblate spheroidairanged with its polar axis extending vertically, a rubber diapbragmyrithin and coaxial with said 6113111 ber, 'said'dia'phragmbeing pre-formed as a bladder which, when in equilibrium, has an upper portion substantially complementary to and engaging theupper'shell wall, and a base portion turned upwardly and inwardly to lie, in

'major extent at least, above the lower edge of said upper portion, there 'beinga pair of fluid flow passages opening through thefshelhone'to thelinterior of the bladder and the other to the'tchamberat a point below the bladder, the axis of said other passage being'coincident with the axis of'the chamber, a centrally arranged stopper carried'by said base portion and adapted to close said other passage when the diaphragm is 'fully' distended by predominant fluid pressure existing within the bladder, and a stabilizer centrally attached to the inner face of thebase portion of the bladder, the stabilizer and stopper being coaxial, said stabilizer-having a vertically resilient, radially outwardly extending portion overlying, but unattached to the base portion ofthe bladder,

10. A dame as in claim 9, wherein said stabilizer comprises 'afrnember of disk-like formation which is centrally attached '-to said stopp'er. i

11. A device asin claim 9, wherein said stabilizer comprises a rubber member of-disk-like formation, the rubber of-the stabilizer b'eing stiifer than the rubber of the bladder.

12.-'A=,device as in claim 9, wherein, when said diaphragm is inequilibrium, the base portion includes an upwardly pointing substantially conical extent and the radially outwardly extending portion of the stabilizer lies in a substantially horizontal plane and is thus angularly spaced from said conical extent.

13. An assembly for the purpose described, comprising a pre-formed flexible bladder having a central base portion adapted for flexible displacement along a central axis, a stabilizer mounted within the 'bladder, said stabilizer being connected to the base proximate said axis andhaving a portion'extending radially outwardly relative to said axis in overlying but unattached relation to said base, said stabilizer portion being axially resilient and being-adapted to' flex when in contact with theinner surface of the 'base during said displacement;

14. An assembly for the purpose described, comprising a rubber diaphr'agm-having a circular periphery, and.

a stabilizer comprising a'rnember centrally attached to the center of-thediajahragrn and having a radially outwardly extending portionoverlying but unattached to the diaphragm, s'aidfmember being flexible and axially resilient and being of rubber which is stifier 'thanis'the rubber of the dia'phragm.'