ysgb1b1 - MIL-STD-188everyspec.com/MIL-SPECS/MIL-SPECS-MIL-G/download.php?...MIL-cAittl35114F 15 J...

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AittlMIL-c 35114F15 J AEN 1969

SupersedingMIL-P-551.4E140ctober 1963

MSLITARY SPECIFICATION

WAND DEm2i;,pAcmGS, tiRAtiHC, cmmw REQ~” FOR

This specificationis mandatory for useby all Departmentsand Agenoies of theDepartmentof Defense,

1. SCOPE

1.1 scoDe.- This.specificationcovers basic design criteriarecommen-dations for use and applicationin packin@, gaskets, packing and gasketglands (see 4.2), and related features for use in hydraulic equipmentutiIized“in systems designed in accordancewith MU-H-5440.

1.2 Classificat*on.- Hydraulic system packingsand gaskets shall-beofthe followi~types and classes: .,

.,

Temperature.ran&e-65o to-I-160°’F.. - - . .

-65° to+275°°F .

-65o to.~450QF.. ~~- ~ .. - ;. . .. .

; Types.T @-’”

&pe III.Classes

Clas9 1; 1,S00 psi -Where the-iuiitoperating~essure at the packingis anormal l,500.poundsper square inch (psi).

Class 2, 3,CW psi -Where”theunit operatiqg @essure at the”packingis a norma13,000 psi.

,.

...

2. APPLICtiLEDCEtiTS “’ . -..

‘2.1 The follokng doc&&$&, o~ thefor bids or request for proposal,formatent specifiedherein: -

*“ SPECIFICATIONS “’

Mmtaq .

MILP-551O - ‘- “.-.

~L-P-5516

MI-L-H-5606

Mm-P-25732 ..‘.

.“Y

issue in effect on date ofP@ of t&. specification

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,.. .

invitationto the ex-

..: :-..

Pa&ing; PreformedStraight Thread TubeFitting 30SS

“PackingPreformed,PetroleumHydrauM.cFluidResistant, 160°F

Hydraulic Fluid, PetroleumBasej Aircraft,Missile and Ordnance

Packi!uz,Preformed,PetroleumHydraulicFluidResi&nt, 275° F

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Downloaded from http://www.everyspec.com

..-.-

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. . . . .. . . .. . .. . .. ... ..

Retainer, Packing Backup, ContinuousRing, . .Tetrafluoroet~lene

Packing, D-Ring, Shock StrutRetainer, Packing Backup, Tetrafluoroethylene,.StraightThread Tube Fitting Boss ““

Retainer, Packing Backup, SiX@ Turn>Tetrafluoroethylene

Packing, Preformed,Hjdraulic,+275° F (O-U).. . .,.

Packing, Pr6form6d~Straight mead Tibe FittingBoss

Retainer, Packing, Back-Up, T.etlonRing, Gasket, Back-up, TeflonFitting End,,StandardDimensionsfor Flareless Tube.Connectionand Gasket Seal ~

Fitting End, Standard Dimensionsfor BulkheadFlareless Tube Connections - ‘

Fittinm, Installationof Fkreless ?hbe, Straight-“Thre;cl&dConnectbis ~“ --

MS33656 Fit~ing End, $tandafidDimensionsfor Flared-Tube .Connectionand Gasket Seal

~33649 Bosses, Fluid Connection- InternalStraight Thread

~33657 Fitting End, Standard ~“nsio~-s for Bulkhead F&redTube Connections .“. ‘“ ~~

....

AN6227 Packing, O-Ring Hydrati-c”T 1..=.

AN6230 Gasket, O-Ring Hydraulic- -.. . -:

... . .

AND~&64:- ~ ~~’‘ “- ..

--.:%,..-

Fi&&v, In@atition .of””FJ.ared!h.&j Straight:>~..T@ade@ comectors ‘~- . . - :.-. -+-,..”’ ....:,- .. ... ....-”. . ........

(Copiesof specifications,star+dards,drawings,an~c&bli;ations r~uiredby supp~ers h connection~th specific procur~ent .gn~tions sho~d ??e”obtained from the procuring activity or as directedby.thticontractiilg-officer.)

“2.2” &h&”’& bl;ica:tionb;- he “follo@@ docukWt .for&sa @rt’of thisspecificationto the extent specifiedherbin.-Unless btherwise--ind.icated,’

the issue in effect on date of invitationfor bids or request for pti~”salj

shall.apply. ... - :... -..,.-...

United States of America Standards Institute.... ..-.

.

-,- . USASI B46.1’-’1%2 “ “--Surface T&ure (Surface’RoughessjWaviness, and Lay) - ~ .!-” .

(ApplicationforStandards Institute,

copies should be addressed to the United States of America10 East 40th Street, New york, Nswyork 10017.)

* ,.

2.

.


. .. 3* RfwIREMmrrs

3.1 General d.esim requirementsfor hydraulicunits,-

3,1.1 Installationof @ckiruzs.- Mechanisme shall be so designedthatno damage to the packingswould be incurred on installationby passingthepackings over threads or other sharp corners. The diameters orthreads overwhich, or through which, packings confined in glands must be inserted at in-stallation,shall be of such size that there will be a diametrical cl~ancebetween the packings and the thread at the most unfavorable extreme tolerances.Chamfered edge annular undercute shall be used at all cross-holes;in addition,chamfers shall be used at the ends of bores with sloped areas clear of inter-secting holes. This is required because where a packing under squeeze (see 4.2)crosses even a round edge cross-hole,it may be partially severed as a reetiltof localized protrusion. ‘!&picalmethods of undercuttingand chamfering,aswell as illustrationof pinched Packingsjwhich are to be.avoided,”.areshownin figure 1.

3.1.2 @eration over unrestrainedareas.- Mechanismswhich require tlu.tthe packing pass over holes, ports, stepdiameters, etc.) wfich would leave theID, OD, or sides of the seal (see 4.2) unrestrainedduring its normal operation,shall be avoided. If, however, it is necessaryto deviate from the above,qualificationtests satisfactoryto the Servicesmust be performedto substan-tiate the design.“In such testsj considerationshall.begiven to: (a) Ueeof the appropriatehighest swell-approvedpackings, (b) aging in the appropriatehighest swell-approvedfluidi (c) adverse maximum packing squeeze if such te,st“conditionsare warranted by analysis of the particular-design. The Services.willdesignate the app13.cablehigh-swell packing and fluid upon request.

3.1.2.1 Dynamic seal (5ee 4.2) travel.- A runr&g seal gland shal.lbe solocated in a component that the leading edge of the groove or gland, at itsposition of extreme travel or adjustment,including adverse tolerances,“shallremain sufficientlytistant from the nearest”edge of w chamfer~undercut> Orother dep%ure from the bore, or equivalentdiameter,that there can be noextrusion, cutting, or other damage to the seal throughoutthe o.perat@g~essureand temperatureranges. In general, the same practiceapplies tb static seals(see 4.2).

3.1.3 Gland materials.- Materialsused in-the manufactureof packingglands shall be in accordancewith the require~nts of the detail specification.All material used in packing glands shall satisfactorilyresist corrosionduringits normal service life. ... .

.-.

3.1.4 o-rim? M ckiiuzgland dimensions.- O-riqg packing glands, bothnominal and otherwise, should be made to the recommended”requirementsindicated -herein. A nominal O-ring installation.shall be consideredone that uses-acylinderbore or piston rod having the equivalentdimensions (see figure 2) andcorrespondingto the,o-ringsas listed.intable I herein. Nominal glands shallbe used wherever possible. “

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KU4-5514F

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. . .

FRERIu3101NGtim

r.”. . .

m_oRN!!i - TO FACDITATEASSEMBLY* X GREATERTHAN Y

.BE~ OX PAOKXNGINS’MLLATIOH

..-

.... .

mu?TION

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‘iRossDlmLED.. . -.-

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. .. . .

.P* INSTALLATION,-

UNDERCUTBORE AS INDICATED

. .

FIGURE 1. Methods to avoid-sharpinstallation’corners-*

4@


MIL-G-551@

BREAK EDGE 4005 ‘*005.-.GOQ.

. !lilESE~A= SEALL BE CONCENTRIOWITHIN THE LIMITS OF TABLE I

-r

A MALE GLANDBORE DIA D CUARANCE (a) (b)

GROOVE DETAIL (c) z

r;cmAMNm“)(b+ rB FEMALE GLAND -“SLEEVE OD,- .

#akar&dlrl~GI-- ...\sG*IS.S

E FEMALE GLANDGROOVE ID

HOUSING BOREix!- ‘ I ‘H lWULE GLAND

A CYLINDERBORE d L F PISTON GROOVE z E ROD GIAND-DIA

(a)

[: 1

(f)

(g)

DIA GROOVE DIA

(SEE TABIZ I lWZ DIMENSIONS.) - “

mAMEJXUCAL C*CE IS THE .Tm.U D~cE -N T~ Bo* ID :AND THE MEMBER CONTAINED THEREIN.SEE 3.5.41F USING STATIC O-UNG S=.TCYIALINDICATORREADING, BEIY@N GROOVE AND ADJACENTBEARING SURFACE● --SEE GROOVE DETAIL●

ONE m TWO NONEXTRUSIONR~GS SHALL BE -mED m AccmANcE iJITH3:4.% “CAUTION SHOULD BE OBSERVED TO INSURETHAT ‘I’@lRADIUS USED AT THE BOT?.OMOF THE GLAND DOES NUi’RESULT IN NOTCH S@lSITIVIl?OF THE GLAND DESIGNOR CREATE AN INSTALLATIONPROBLFJLFOR THE GROOVE ANGLE, BE1’TERPERFOIU?MNCEIS OBTAINEDAT THE O DEGREEANGLE,EITHER THE GROU~ DIAMETER DIMENSIONOR THE OPPOSINGSJMIJNG SURFACE “DIMENSIONMAY BE HELD WITHIN CLOSER LIMITS THAN THOSE SPECIFIED.TOGAINADDITIONALMACH3N13!JGTOLERANCE ON ITS OPPOSINGDIMENSION,PRUtIDEDTHEACCUMULATEDTOLERANCE OF THE TWO DIMENSIONSDOES NOT EKCMD THAT SPECIFIED

EXAMPLE: F@ AN MS2S775-ZZLO-RING..-.‘AtlDIAMETER MAY BE HELD TO le678/1*679IN LIEU OF 1.678/I.680TO GAIN AN l~FnDIAMETERDIMENSION OF 1.435/1.432“IN~U OF 1.435/1-433s

FIGURE 2, Gland design “.5 ....


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NII.A2-55UF

TABIE I (Continued)

NOTE: Caution should be used in appl@ng the -001 through -005 sizes.While bein&installed inan externalgroove, they might bestretched beyond the elastic lhitj with probable failures orincipient failures re9ulthg. Mbreover, there is no standardbackup ring for -001 through -003; therefore,for pressuresin excess of 1500PSI the diametral clearance (extrusiongap)must be reduced.

It is recommendedthat wherever possible,O-zd.ngswith a largercross sectionaldiameter (Wt’ dimension)be used in preferenceto -020 through -028 and -131 through -49,s0 as to provid6 amore adequate seal. Therefore,these sizes are not preferred.

10

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MIL-G-5514F

3.1.4.1 Nominal sized installations.- Dimensionsj tolerances,andallowable eccentricitiesfor piston rods, cylinder bores, and rod and headgland groove diameters, lengths and shapes, and allowable diametricalclearances fornominal O-ring installationsshall be carefully selected andclosely controlled in order to provide for required service life?’preventionof extrusion,minimum leakage, and freedom from binding throughout the requiredrange of operating temperaturesand pressures. For glands to seal up to andin-eluding2,500 psi pressure, the data given in table I of this specification,under the co,lumntitled“NO backup rings,ttare suitable for type 1 systems.For glands to seal up to and including 3,000 psi pressure, the data given intable I of this specificationunder the columns titled “One backup ring” and“TWO backup ringsl’are sqitable for type 1 and type 11 systems.

3.1.4.2 -.Otherthan nominal sized installations.- Glands of sizes otherthan nominal will be referred to as nonstandardherein. The use of non-standard gland cylinder bores, piston rods, etc., shall be”held to a minimumconsistentwith the design performance and weight considerationsof the com--ponent. When a nonstandardbore or rod is used, the closest standardpackingdash number shall be selected as determined from the nominal packing size aslisted in table I. The selection of packing size in a nonstandardgland shall Ibe based primarily onthe considerationof performance. The nonstandardgroovediameter and dimensions pertaining thereto should be calculated in the samemanner as for standard nominal glands by the foimulas of table I. However,where O-rings are stretched, considerationshould be given to low-temperatureleakage, since the stretch and shrinkage combine in reducing the O-ring’scross-sectionalarea. In addition, when using nonstandardgland dimensions,great care in the selection of a nonextrusion device must be taken. Forexample,MS28782 rings cannot be used indiscr~inately on nonstandardglanddimensions.

3.1.5 Qualificationof special packing glands..-When packing gland designsdiffer from the recommendeddesign practices as given in this section, or designconditions in the component dictate, the particular gland shall be qualifiedbyteststsu”itableto the prouuring activity. The Serviceswill base their require-ments for such tests on past Service experience and laboratory tests> and mayrequire the use of ,particularmakes of approved packings, gaskets~ and fluidsin the qualificationtests.

..,

3.1.5.1 Service experience has shown that low squeeze O-ring installationsdesigned to provide reduced O-ring friction’areunsatisfactory,although thelow squeeze installationmay have passed qualificationtests. For this reason,a d“esignO-ring squeezethat is less than the minimum value specified in table Ishall be tested to adversetolerances. This shall be accomplishedby the use ofMIL-H-5606 low swell.fluid specified.’bythe Services and machining the O-ringgland to provide the low limit of design O-ring squeeze.

11


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MIL-G-5514F

3*2 Standard packings.-

3.2.1 Type I systems.- A1l packings used in hydraulic equipment fortype I systems, designed in accordancewith this specification,shall bestandard-approvedpackings conforming to MIL-P-5516,AN6227, AN6230, andMS28772.

3.2.2 J$ype II systems.- All O-ring packings used in hydraulic equipmentfor Cype 11 syslxms, designed in accordancewith this specification,shall bestandard-approvedpackings conforming to MIL-P-25732and MS28775.

3,2.3 Type 111 systems.- Since there are no standard packings presentlyavailable for use in type 111 hydraulic system equipment,any packing instal-lation selected for this temperaturerange shall be qualified inzthe componentand subsequentlyapproved by the procuringactivity based on the componentqualificationtest.

3,2.4 Use of O-ring packings.- O-ring packings are intended for use asstatic or running seals in hydraulic system components. If used as runningseals without nonextrusiondevices, the O-ring seals shall be used only atoperatingpressures not greater than 1,500 psi in types I, 11, and III systems,unless the extrusion gap is maintained small enough to prevent extrusionofthe O-ring for the life of the componentat the highest pressure. Usage withnonext??usiondevices is specified in 3,4. O-ring packingsmay be used forstatic seals. Design and installationdetails for such use are specified in 3,5.

3.2.4,2 Use of D-ring Packings.- D-ring packingsare intended for use asrod seals only in landing gear shock struts. The D-ring packing is designedprimarily for use in lieuof the O-ring packings in landing gear installationswhere spiral failure of the O-ring packing is a problem. It may be used withoutbackup or wieh one or two backup rings (see 4,2), dependingon the pressure,deflection,and other requirementsof the specificutilization. For thediametricaldimensionsof the installationof D-rings, the dimensionsestab-lished in table I for O-rings are recommended. For groove width (dimensionsllG1t),the dimensions of table 11 are recommended. The MS28772 D-rings in theirfull range of sizes are equivalentin ID and OD dimensions to the MS28775O-zings in sizes -335 through -460.

-..

* 3.2.5 Surface finishes of glands.- The following surface finishes shall beused in units containingO-ring packings, unless performanceor qualificationtests indicate that other surface finishesare satisfactory. These finishesare indicatedas surface roughness as defined in USASI B46.1 - 1962.

Surface roughnessPart of Unit height rating

Cylinderbor or piston rod (diameterover which packing must slide) 16 (max.)

O-ring groove diameter:Dynamic seals 32 (max.)Static seals 63 (max.)

O-ring groove sides when no backup ring is used:Dynamic seals 32 (max.)Static seals 63 (max.)

O-ring groove sides when backup rings are used 63 (max.)

12

.-


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MIL-G-5514F.

‘l%egroove surfaces must be free from all machining irregularitiesexceedingthe above values, scratches,etc. Groove edges shall be smooth and true andfree of nicks, scratches,burrs, etc.

TABLE 11. D-ring gland width dimensionst .— .———

[.——

Groove width “G” ~/—.

Dash No. No back- One back- Two back-

1

—. up ring up ring up rings—---------.--- --... .-.________

-335 to -349 0.424 -0.5!37 0.597.434 .517 .607----------------.......---.....--...--------.----”.-.-.. .-..-.....--............_

-425 to -460 .579 .729 .854.589 .739 .864

~/ See (d) of figure 2.

3.2.6 O-ring groove shape.- Rectangular type groove shapes, following the

general design criteria of table I, are preferred. The grooves may have up to~ degrees sl~pe on the sides to facilitatemachining; the radius in the bottomcorners of the groove must be a compromisebetween strength requirements, typeof nonextrusion device, and adequate groove volume. When TFE (see4.2] ringsare used, the radius must be a minimum consistentwith installationand perform-ance requirements. The width of the groove shall be consistentwith theperformancerequirementsof the gland and the type of nonextrusiondevice used.Considerationshould be given to cross-sectionalsqueeze and volumetric swellof the O-ring owing to oil immersion and temperature. The recommendedgroovewidth dimensions are shown in table I. Narrower grooves make it more difficultm remove the O-ring for inspection and replacementand increase the possibilityof nicking and scratching the edge of the groove during removal of the O-ring.The outer corner of the groove must be smooth with the corner broken slightlyto prevent sharpness. Too large a corner radius will contribute toward localfailure. This effect will be greater with increasedoperating pressures andtemperatures.

3.2.7 Number of G-rings per gland.- The use of two or more O-rings in thesame groove or in adjacent grooves can,produce pressure traps between the adjacentO-rings and a subsequent rise in temperaturetakes place causing thermal expansionof the fluid or lubricant. Such conditionshave caused jamming of units inservice. If the use of two or more O-rings are required for some design reason,adequate provision such.as venting of the space between the O-rings~ must bemade m prevene pressure trap.

I1-

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MIL-G-5514F

3.2.8 Breathing.- The piston head gland of actuating cylinders andsimilar componentsin which the gland is confined by a lightweightcylindricalmember, which breathes diametricallyas pressure is applied,may have a totaldiametricalworking clearance greater than that shown by the clearance columnsof table I in type I systems. Experiencewith actuators up to 5-1/2 inch borediameter has indicated that the diametricalbreathihg,owing to pressure appli-cation only~ should not exceed approximately0.0020inch per inch of borediameter at the sddpoint of the cylinderbarrel with the piston bottomed at oneend of the cylinder! The breathing should actually be less than 0.0020 inchper inch of bore diameter in the transverseplane immediatelyadjacent to thenormal actuatingcylinder piston head seal~ owing to decreasingcylindermaterial flexure at this point, Breathingwill usually be less in small-diameter low-pressurecylinders owing to manufacturingconsiderations. Inlarge diameter cylinders,or units which have large values of diametricalbreathing,tests will have to be made the satisfactionof the procuringactivity to insure adequate life of the seal and gland.

3;3 Nonstandardhydraulic packings.-1I 3.3.1 Use of nonstandardhydraulic packings.-

303.1.1 Type I and type II systems.- When a satisfactoryInstallationusing standardpackings is not possible owing to performancerequirements,nonstandardpackings such as TFE cap rings may be used, subject to approvalby the procuringactivity, and provided the unit satisfactorilycompletesqualificationtests.

3.3.2 Design considerations.- On nonstandardpacking and packing glanddesigns, considerationshall be given to the design applicationand the followingpoint shall be noted: Surface finish, extreme temperature,sealing, low-pressureand high-pressureleakage, air inclusion as a result of servo operationwithoutfluid pressure, etc.

3.4 Noq~trusion devices.-

1 3.4.1 Applicationof nonextrusiondevices (backuprings).-

3,4,1,1 Type I and type II systems.- Where required, to permit a componentto conform to performanceor qualificationtests, nonextrusiondeviceswithinthe packing gland may be used, At lower pressures,nonextrusiondevices,willprolong the normal wearing life of the O-ring and, at higher pressures,non-extrusiondevices pemit greater diametricalclearancesbetween mating parts.Unless otherwiseapproved by the procuringactivity, the applicablestandardpackingsand backup devices shall be used.

3,4*1,2 Type III systems.- Packings and backup rings for use in type 111systems shall be designed in such manner as to fulfill the performanceandqualificationtest requirementsof the individualhydrauliccomponent.

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. MIL-G-5514F

3.4.2 Glands for packings and gaskets with nonextruiondevices.- Glandsfor combination of packings with backup rings and for gaskets with backup ringsshall be designed to the same considerations as for nominal rectangulargrooves,

but with the following additional considerations. The width of the groove is ofgreat importance,“sincea groove which is too wide may permit the backup ringsto roll and thus.become.ineffectiveas a nonextrusion“device. Angles in excessof 5 degrees on the side of the groove may produce the same result. A groovewhich is too narrow qay”cause high friction and extreme difficulty on instal-lation. -Thedata shorn in table I have been found to be acceptable anddesirable. Glands for TFE.nonextrusiondevices must have corner radii consistent.’with the performance and cross-sectionalrequirementsof the TFE backup rings;otherwise difficult installationand operation problems may result.

3.4.3 Installationof nonextrusien rings.- The use of two backup ringsin each gland, one on either side of the O-ring seal, even though the pressureapplication is from one side only, is desired in all cases to facilitatestandardizationof groove dimensions and service procedures. Where it is self--evident,however, that pressure can be applied from one direction only, andspace limitations to provide for tmrings create a hardship, a single backupring may be used; this ring to be placed on the side of the O-ring away fromthe pressure. When the pressure differentialacross a packing is unidirectional,onl”y one backup ring need be installed. This backup ring shall be on the low-pressure side. The groove width dimensions shown in table I for one backup ringmay be used, as applicable.

*“ 3.4.3.1 Continuous turn TFE backup rings.- A continuousTFE ring may beused for new designs. Installatioriof the small sizes of this ring into thegland will probably require use of split- or multiple-pieceadapters; Continuousturn backup rings shall be in accordancewith the uncut sizes of MS28774. For AirForce use, continuous turn backup rings shall be in accordance.withMS27595, orthe uncut sizes of MS28774.

3.4.3.2 Spiral TFE backup rings.- Great care must be exercised in theinstallationof spiral TFE backup rings. If the groove radii are large forstructuralreasons, the spiralsmay be sheared upon”installation. Therefore,it is important that when installing spiral TFE backup rings that the mating partbe rotated in the proper direction, so that the spiral will tend to wrap itselfdeeper into then-grooveand will not be sheared,off when the parts are assembled.Spiral TFE backup rings shall be in accordance.with MS28782 and MS28783.

3.4.3.3 Single-turnTFE backup rings.- This ring may be used for new designs.It is the simplest to install and does not require any special installation pro-

cedures. Single turn backup rings shall be in accordance with MS28774.

3.5 Static seals.-

3.5.1 Type I and type 11 systems.- All nonmovingpackings (static seals)used for sealing of fluid pressures shall be standard-approvedstatic seals.These static seals shall not be compressed into threads or against other ir-regular or rough surfaceswhich would cut or c)therwisedamage them. Recommendedstatic seal glands are shown in table I. The groove fillet radius and the fatiguerequirementsshould receive-verycareful consideration.

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MIL-G”5514F

3.5,2 Type III systems.- StaticEype 111 syseems shall be designed in

.

seals and backup rings for use insuch manner as to fulfill the perfor-

mance and qualification test requirementsof the individualhydraulic component.

305,3 o-ring gasket seals,- O-ring gaskets conforming to part nos.AN6230-1 Chrough -25 and MS28775 -013 through-028, -117 through -149, and-223 through-247 are intendedonly for use as static (nonmoving)sealsand shall not be used as dynamic (moving)seals. All the detail requirementsspecifiedfor O-ring packings will apply to the use of O-ring static sealsconformingto pare nos, AN6230-1 through-25, and MS28775-223 through -247,except as noted in the followingparagraphs.

3,5.4 Pressure limitationsand use of O-ring static seals.-

3.S04,1 Type I systems,- Static seals conforming to AN6230 may be usedat pressures up co and including 1,500 psi, provided the clearances,eccen-tricities,and other requirementsof table I are not exceeded. Above 1,500psi pressure, the AN6230 O-ring static seals and the sizes of AN6227 O-ringpackingsused as static seals, shall be used with the applicablebackup ringsin accordancewith table I. If the diametricalclearance can be held to amaximum of 0.0025 inch under the worst conditionof tolerances,eccentricities,breathing?etc.~ the backup rings need not be used. The use of AM6227 packingsas static seals in lieu of AN6230 static seals is preferred in all sizes.

3,5,4.2 Type 11 systems.- Static seals conformingto MS28775 should beused at pressures up to 3,000 psi with backup rings in accordancewith table Iand requirementsherein on nonextrusiondevices, unless it can be proven byqualificationtests that glands will perform satisfactorilywithout nonextrusionbackup rings. Leather backup rings shall not be used in type II systems.

3,5.5 Use of.straight thread tube fitting boss gasket.-

* 3,5.5,1 Type I systems.- The gasket for type I systems is a 90 ShoreDurometerO-ring gasket, defined by MS28778 and MIL-P-551O.This gasket isnot suitablefor interchangeableusage with MIL-P-5516and MIL-P-25732 sealsowing primarily to lack of flexibilityat cold temperaturesand lack of re-silience. For this reason, the MS28778 gasket shall be used only in connectionwith straight thread tube fitting glands, such as in the boss conforming toMS33649,with end fittings in accordancewith MS33656 and MS33657 assembled inaccordancewith AND1OO64; and MS33514 and MS33515 assembledin accordancewithMS33566, This usage includes such other parts as end cabs an check valveswherein the dimensions of the gland duplicate the tube fitting and boss drawingsenumeratedabove. In certain fitting installations,as shown on AND20064,the MS28773 nonextrusionrings must b,eused with the MS28778 gasket. *

* 3.5.5.2“Type II systems.- The requirements of type 11 systems are iden-tical to type I systems.

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, .<:-. .

/

MIL-G-5514F

3.5.5.3 Type III systems.- Gaskets suitable for the temperaturerangesof this systeiiwhich satisfactorilypass the qualificationtest requirementsof the fitting installationshall be used.

3.5.6 Static face seals.-

3.5.6.1 Type I systems.- The use ofwherever a breathing problem exists and ais feasible. Where static face seals are

static face seals should be avoided

submerged radial squeeze seal design

desired, gaskets conforming to

AN6227 or AN6230, may.be used. In such instzdlationsthe depth of the grooveshall be in accordance with table 1.

3.5.6.l.lDesigndetails.- Metallic surfaces contacting the O-ring faceseals shall have a surface finish no rougher than 32 microinches, in accordancewith USASI B46.1 - 1962. The cap or coverplatemust be as rigid as necessaryto prevent excessive breathing which would introducean extrusion gap at thejoint. The important feature in face seal design is to provide squeeze on thegroove section and prevent any possible radial movement of the O-ring uderpressure application. Provisions shall be made to insure that the O-ring cannotbe displaced from its groove under any flow or pressure condition.

3.5.6.2 Type 11 and type 111 systems.- Static face seals, suitable for thetemperatureranges of these systems, shall satisfactorilypass the qualification.test requiremen~sof the installation to be used. Usage of MS28775 seals isrecommended for typeII systems.

3.6 Design data on use of dynamic and static seals.-

3.6.1 Design data.- The design data coxitainedin this section are intendedto supply the designer with the basic fundamentalreasons behind the requirementsof this specificationand the results which may be expectedwhen there is de-viation from those requirements.,Typical installationof static seals is shownin figure 3.

3.6.2 O+ing squeeze.- Referring to table I, the O-ring squeeze isrepresentedby the differencebetween the free O-ring cross-sectiondiameterand dimensions A-F or E-B (as applicable).

--=?- T

3.6.2.1 Type I systems.- In order to produce an acceptable product thatwill perform satisfactorilythroughout its normal life, it is recommendedthatO-ring packing squeeze and dimensions listed in table I be used. The minimumsqueeze and dimensions shown in table I are so establsihed that with all tol-erances, clearances, eccentricities,side loads, and linear contractionof thepacking compound taken into consideration,there will still be a positive in-terferenceremaining on the O-ring secticm throughout the temperaturerange ofthis type system.

17


.

.,. .

MrL-G-551LF

\

O-RINGS IN ACCOXDANCE”WTTHSTANDARDAN6227 0RAN6230

METALRETAINER

rQWNGS IN ACCORDANCEWTH PRE&RESTANDARD AN6227 0RAN6230

I—~

PRESSURE

~v?i!!!3K:?,.R,.PA-CUUM JWPLI TAPERs

NM II A

[OBTAINjmmiWONSFRO]:TARLE

SW30E8TEDFACE SEAL GLAND DIllEl@?ONS

SPRIM3

T\A..J

ENLARGED VIEM A

ADJUSTMENT SCR.EULOCK

FXWRE

SECTION OFO-RING

EXE PLIX3SEAL

3. Typical installationof static seals18


MIL-G-5514F.

3.6.2.2 Type II systems.- For these systems, it is recommended that theO-ring packing squeeze dimensions listed in table I be used. However, sinceinsufficient test informationis available as of the date of this revision,other squeeze dimensionsmay be desirable for particular applications.

3.6.2.3 Chan”geof squeeze considerations.- The following items wereconsidered in setting up the dimensions shown in table I for type I systemsand must be given due considerationwhen deviations from these dimensions are

For type II systems, these considerationsmay not be directly applicable.made.

3.6.2.3.1 Decrease squeeze.- Decreasi~g the squeeze will slightly reducefriction and breakout under low hydraulic pressure (under 500 psi) operatingconditions. When reduced squeeze is used, a better surface finish is usuallyrequired for low-pressuresealing. The saving in friction will be neutralizedat high pressures owing to compressionof the O-ring into the end of the groove.Figure 4 illustrates this condition as well as positions of packing in theirgrooves under various degrees of pressure. “Breakoutfriction of O-ring typepacking will be higher than running friction, being dependent on factors.ofsurface finish, time, pressure, squeeze, etc. Particular care must be taken toinsure that low-pressureand low-temperatureleakage is not encountered.

3.6.2.3.2 Increase squeeze.- Greater O-ring squeeze than specified intable I may result in greater assembly problems, requiring larger or flatterangle levels, or both, at shoulders,etc., (see figure 1). Increasing thesqueeze will also tend to increase the scrubbing and rolling-of the O-ringduring operation which may in turn result in shorter packing life. The frictionat low-operatingpressure will be increased. The greater squeeze may, however,result in lowering the critical cold temperatureof the unit from the standpointof low-temperatureleakage. When squeeze is increasedbeyond that shown intable I and backup rings are required, those listed in table I cannot be usedowing to interference.

3.6.3 Diametrical clearance.- The greatest factor in reducing the lifeof O-ring packings is the extrusioriof”the O-ring into the clearance gap.The @earance consequentlyshould be held”as small as practicablewith specialattention given to factors such as thermal expansions,pressure expansions~side load.,eccentricities,type of motion, and other basic considerationsofsurface finish, lubrication,and accuracy which affect O-ring life. Backuprings or ncmextrusion devices permit the use of slightly larger gaps. Dia-metrical clearance is the total difference between the diameter of the bore”and the diameter of the member contained therein.

3.6.4 General limitationsof O-rings.- O-ring packings and gaskets havesome general limitationswhich should be kept in mind when designing hydraulicunits. Some of these limitationsare as follows.

19


—,,. .

“.

.

.

.

SIQN

REOTAI?GULAR

FIGURE L,

~ ZEROPRESSURE

~ 1,000 PSI PRESSURE

-- l,@psI pREss~

~3,000PsI PRESSURE

RONEXTRUSIOMRiM3S

Relative psitions of -ring packings indifferent grooves at increasingpressues

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MIL-G-5514F.

3.6.4.1 Friction.- In some units,.such as surface control boost.cylinders,the breakout friction of O-rings can cause undesirabledrag, which if not takeninto considerationin the original design, may produce designs which are notsuitable for the purpose intended. Breakout friction is caused by the extrusionof the p“ackingmaterial into the surface irregularitiesof the mating surfacesor adhesion, or both, of these materials (see 3.6.2). Breakout friction ofO-rings is higher than running friction. All standard paqkings have someminimum frictionvalue which cannot be materially reduced by practicalmethodsof design. When ”frictionproblems are encounterecl,a special gland installationshould be considered preferable to special packings (see 3.6)”.

3*6j4:2 Oscillation.- O-ring packings, when used to seal rapidly oscil-lating mechanisms, have not always proven successful in past installations.Special studies must be made in designs of this type to provide for proper lifeand performance.

3.6.4.3 Rotary seals.- Standard packings are not specificallydesigned asrotary seals. However, where infrequent rotary motion or low peripheralvelocityis required, they may be used, provided consistent surface finishes over the en-tire gland are used and eccentricitiesare accurately controlled. In addition,the use of low-frictionnonextrusion devices have been found to be helpful inprolonging life and improving performance.

3.6.4.4 Precaution.- Glands in which the O-ring is seriously deformed ordistorted by crushing or other loads (stretchingand twisting) can.induceper-manent set and disintegrationin the O-ring. “Increasedtemperaturesor strains,or both, induced in a seal will cause rapid deteriorationof the seal owing tothe strain aging and permanent set properties of seal compounds.

4. NOTES

4.1 Intended.use.- The procedures covered by this specificationare in-tended to establish gland design and installationmethods of packings andgaskets for use in hydraulic equipment design itiaccordancewith MIL-H-5440.

4.2 Definitions.- General terms used herein are defined as follows:

(a)

(b)

(c)

(d)

Squeeze: The dimension by which a packing is distorted from itsmolded shape when installed in a packi~~gland.Seal: A device to retain fluid within a hydraulic component.The seal may consist of two or more components,such as a packingin a gland, and a packing and backup ring.in a gland, etc.Packing: The component of a seal whdkhserves as a sealingmedium by nature of its plastic or elastic properties, or itsability to deform int-othe shape of the gland.Gland: The component of the seal which forms the cavity orinclusionwhich surrounds and supports the packing and controlsthe squeeze.

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MIL-G-5514F

(e)

(f)

(g)

(h)

(i)

Gasket: A type of seal wh$ch if formed by crushing the packingmaterial into the gland such that the cavity formed by the glandis normally filled with the packing ❑aterial.Dynamic seal: ~type of seal where there is relative motionbetween some part of the gland and the packing, such as a pistonor shaft seal.Static seal: A type of seal where there is no relativemotionbetween the packingzndany part of the gland, although limitedfreedom may be provided to permit the packing to change itsshape within the gland when under pressure,Backup ring: A device used to prevent pressure and friction fromextruding the G-ring packing through the clearancegap of a seal,TFE: A tetxafluoroechyleneresin.

* 4.3 Marginal indicia.- The margins of this specificationare marked toindigaeewhere changes> deletions,or additions to the previous issue have beenmade. This is done as a convience only and the Government assumes no liabilitywhatsoeverfor inaccuraciesin these notations. Figures are not so marked.Bidders and contractorsare cautioned to evaluate the requirementsof thisdocumentbased on theentire content as written, irrespectiveof the marginalnotationsand relationship to the last previous issue.

Custadfans: Preparing activity:Army - Av Air Force - 11Navy - ASAizrFor.ce- 11 Project No. 5330-0158

* Revieweractivities:Army - AV, MI, MR, WCNavy - AS, SHAir Force - 11, 71, 82

* User activities:Amy - GLNavy - MC ..

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