DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited. NONRESIDENTTRAININGCOURSE July 1990Fluid PowerNAVEDTRA 14105 DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.Althoughthewordshe,him,andhis are used sparingly in this course toenhance communication, they are notintendedtobegenderdrivenortoaffrontordiscriminate against anyone.COMMANDING OFFICERNETPDTC6490 SAUFLEY FIELD RDPENSACOLA, FL 32509-5237ERRATA #3 19 Oct 99SpecificInstructionsandErrataFLUIDPOWER1. This errata supersedes all previous erratas. No attempt has been made toissue corrections for errors in typing, punctuation, etc., that do not affectyour ability to answer the question or questions.2. To receive credit for deleted questions, show this errata to your localcourse administrator (ESO/scorer). The local course administrator is directedto correct the course and the answer key by indicating the question deleted.3. Assignment BookletDelete the following questions, and leave the corresponding spaces blankon the answer sheets:Questions2-62-92-153-5Questions4-525-225-67Make the following changes:Question1-191-523-324-154-184-285-85-52/5-555-67ChangeInthequestions, change the question to read "In themetric system, the density of a substance is expressedas..."In the question, line 5, "60 cubic centimeters"isequivalentto60milliliters.In the blurb before the question, line 2, delete "and3-33."In alternative 3, change "form" to from."In the question. line 2, change "instead" to "installed."In alternative 2, change "el" to "element."In the blurb preceding the question, line 1, change "1-8"to "5-8."In the column under "COMPONENTS", in alternative 3, add"mover"after"prime."In the blurb preceding the question, line 2, change"5-71" to " 5-70." iPREFACEBy enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy.Remember, however, this self-study course is only one part of the total Navy training program. Practicalexperience, schools, selected reading, and your desire to succeed are also necessary to successfully roundout a fully meaningful training program.COURSEOVERVIEW: In completing this nonresident training course, you will demonstrate aknowledge of the subject matter by correctly answering questions on the following: fundamental physics asappropriate to fluids at rest and in motion; types and characteristics of hydraulic and pneumatic fluids; majorcomponents of basic fluid power systems and diagrams used to illustrate these systems; proper proceduresand precautions for handling and replacing lines, connectors, and sealing devices; proper procedures foreliminating contaminants; purpose, operation, application of pumps, reservoirs, strainers, filters,accumulators, flow control and measuring devices, directional control valves, and actuators; arrangementand operation of representative fluid power systems including the function and interrelationship of majorcomponents.THE COURSE: This self-study course is organized into subject matter areas, each containing learningobjectivestohelpyoudeterminewhatyoushouldlearnalong withtextandillustrationstohelpyouunderstandtheinformation. Thesubject matter reflectsday-to-dayrequirementsandexperiencesofpersonnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers(ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational ornaval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classificationsand Occupational Standards, NAVPERS 18068.THE QUESTIONS: The questions that appear in this course are designed to help you understand thematerial in the text.VALUE: Incompletingthis course, youwill improveyour militaryandprofessional knowledge.Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you arestudying and discover a reference in the text to another publication for further information, look it up.1990 Edition Prepared byMMC Albert Beasley, Jr.Published byNAVAL EDUCATION AND TRAININGPROFESSIONAL DEVELOPMENTAND TECHNOLOGY CENTERNAVSUP Logistics Tracking Number0504-LP-026-7730iiSailors CreedI am a United States Sailor.I will support and defend theConstitution of the United States ofAmerica and I will obey the ordersof those appointed over me.I represent the fighting spirit of theNavy and those who have gonebefore me to defend freedom anddemocracy around the world.I proudly serve my countrys Navycombat team with honor, courageand commitment.I am committed to excellence andthe fair treatment of all.C ONT E NT SCHAPTER1. I ntroducti on to Fl ui d Power.. . . . . . . . . . . . . . . . . . . . . . .2. Forces i n Li qui ds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. Hydraul i c Fl ui ds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4. Pumps . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .5. Fl ui d Li nes and Fi tti ngs . . . . . . . . . . . . . . . . . . . . . . . . . . . .6. Val ves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7. Seal i ng Devi ces and Materi al s . . . . . . . . . . . . . . . . . . . . . . .8. Measurement and Pressure ControlDevi ces . . . . . . . . . .9.Reservoi rs,Strai ners,Fi l ters,andAccumul ators......10. Actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11. Pneumati cs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12. Basi c Di agrams and Systems . . . . . . . . . . . . . . . . . . . . . . . .APPENDI XI . Gl ossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .I I .Mechani cal Symbol sOtherthanAeronauti calfor Fl ui d Power Di agrams . . . . . . . . . . . . . . . . . . . . . . . . . .I I I .Aeronauti cal Mechani cal Symbol sforFl ui dPower Di agrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Page1-12-13-14-15-16-17-18-19-110-111-112-1AI -1AI I -1AI I I -1I NDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I NDEX-1. . .iiiCREDI TSThecompani esl i stedbel owhaveprovi dedpermi ssi ontousecertai ntradenames/trademarksi nthi sedi ti onofFluid Power.Permi ssi ontousethesetradenames/trademarks i s grateful l y acknowl edged. Permi ssi on to reproduceorusethesetradenames/trademarksmustbeobtai nedfromthesource.SOURCE TEXTONPAGEDuPontGreene,TweedandCompanyMi nnesotaRubber5-87-57-15ivvINSTRUCTIONS FOR TAKING THE COURSEASSIGNMENTSThe text pages that you are to study are listed atthebeginningofeachassignment. Studythesepages carefully before attempting to answer thequestions. Pay close attention to tables andillustrations and read the learningobjectives.The learning objectives state what you should beable to do after studying the material. Answeringthe questions correctly helps you accomplish theobjectives.SELECTING YOUR ANSWERSReadeachquestioncarefully, thenselect theBEST answer. You may refer freely to the text.Theanswers must betheresult of your ownworkanddecisions. Youareprohibitedfromreferring to or copying the answers of others andfromgivinganswerstoanyoneelsetakingthecourse.SUBMITTING YOUR ASSIGNMENTSTo have your assignments graded, you must beenrolled in the course with the NonresidentTrainingCourseAdministrationBranchat theNaval Education and Training ProfessionalDevelopment and Technology Center(NETPDTC). Followingenrollment, there aretwowaysof havingyour assignmentsgraded:(1) use the Internet to submit your assignmentsas you complete them, or (2) send all theassignments at one time by mail to NETPDTC.Grading on the Internet: Advantages toInternet grading are:youmaysubmit your answers as soonasyou complete an assignment, andyouget your resultsfaster; usuallybythenext working day (approximately 24 hours).Inadditiontoreceivinggraderesultsforeachassignment, you will receive course completionconfirmationonceyouhavecompletedall theassignments. To submit your assignmentanswers via the Internet, go to:http://courses.cnet.navy.milGradingbyMail: Whenyousubmit answersheets by mail, send all of your assignments atone time. DoNOTsubmit individual answersheets for grading. Mail all of your assignmentsin an envelope, which you either provideyourself or obtain from your nearest EducationalServicesOfficer (ESO). Submit answer sheetsto:COMMANDING OFFICERNETPDTC N3316490 SAUFLEY FIELD ROADPENSACOLA FL 32559-5000Answer Sheets: All courses include onescannableanswersheet foreachassignment.Theseanswer sheets arepreprintedwithyourSSN, name, assignment number, and coursenumber. Explanations for completing the answersheets are on the answer sheet.Do not use answer sheet reproductions: Useonly the original answer sheets that weprovidereproductionswillnot work with ourscanning equipment and cannot be processed.Follow the instructions for marking youranswers on the answer sheet. Be sure that blocks1, 2, and 3 are filled in correctly. Thisinformationisnecessaryforyourcoursetobeproperly processed and for you to receive creditfor your work.COMPLETION TIMECoursesmust becompletedwithin12monthsfrom the date of enrollment. This includes timerequired to resubmit failed assignments.viPASS/FAIL ASSIGNMENT PROCEDURESIf your overall course score is 3.2 or higher, youwill pass the course and will not be required toresubmit assignments. Once your assignmentshave been graded you will receive coursecompletion confirmation.If you receive less than a 3.2 on any assignmentand your overall course score is below 3.2, youwill be given the opportunity to resubmit failedassignments. You may resubmit failedassignmentsonlyonce. Internet students willreceivenotificationwhentheyhavefailedanassignment--they may then resubmit failedassignmentsonthewebsite. Internet studentsmay view and print results for failedassignments fromthewebsite. Students whosubmit by mail will receive a failing result letterand a new answer sheet for resubmission of eachfailed assignment.COMPLETION CONFIRMATIONAfter successfullycompletingthiscourse, youwill receive a letter of completion.ERRATAErrata are used to correct minor errors or deleteobsoleteinformationinacourse. Erratamayalso be used to provide instructions to thestudent. If acoursehasanerrata, it will beincluded as the first page(s) after the front cover.Errata for all courses can be accessed andviewed/downloaded at:http://www.advancement.cnet.navy.milSTUDENT FEEDBACK QUESTIONSWe value your suggestions, questions, andcriticismson our courses. If you would like tocommunicate with us regarding this course, weencourage you, if possible, to use e-mail. If youwriteorfax, pleaseuseacopyoftheStudentComment form that follows this page.For subject matter questions:E-mail: n314.products@cnet.navy.milPhone: Comm: (850) 452-1001, Ext. 1826DSN: 922-1001, Ext.1826FAX: (850) 452-1370(Do not fax answer sheets.)Address: COMMANDING OFFICERNETPDTC N3146490 SAUFLEY FIELD ROADPENSACOLA FL 32509-5237For enrollment, shipping, grading, orcompletion letter questionsE-mail: fleetservices@cnet.navy.milPhone: Toll Free: 877-264-8583Comm: (850) 452-1511/1181/1859DSN: 922-1511/1181/1859FAX: (850) 452-1370(Do not fax answer sheets.)Address: COMMANDING OFFICERNETPDTC N3316490 SAUFLEY FIELD ROADPENSACOLA FL 32559-5000NAVAL RESERVE RETIREMENT CREDITIf you are a member of the Naval Reserve, youmay earn retirement points for successfullycompleting this course, if authorized undercurrent directives governing retirement of NavalReserve personnel. For Naval Reserveretirement, this course is evaluated at 8 points.(RefertoAdministrativeProceduresforNavalReservists on Inactive Duty, BUPERSINST1001.39, for more information about retirementpoints.)viiStudent CommentsCourse Title: Fluid PowerNAVEDTRA: 14105 Date:We need some information about you:Rate/Rank and Name: SSN: Command/UnitStreet Address: City: State/FPO: ZipYour comments, suggestions, etc.:PrivacyAct Statement: Under authorityof Title5, USC301, informationregardingyour militarystatusisrequestedin processing yourcomments andin preparing a reply. This information will not be divulged withoutwritten authorization to anyone other than those within DOD for official use in determining performance.NETPDTC 1550/41 (Rev 4-00CHAPTER1INTRODUCTION TO FLUID POWERFl ui dpoweri satermwhi chwascreatedtoi ncl udethegenerati on,control ,andappl i cati onofs mooth ,effecti v epower ofpu mpedorcompressed fl ui ds (ei ther l i qui ds or gases) whenthi spoweri susedtoprovi deforceandmoti onto mechani sms. Thi s force and moti on maybe i nthe form of pushi ng, pul l i ng, rotati ng, regul ati ng,ordri vi ng.Fl ui dpoweri ncl udeshydraul i cs,whi chi nvol ves l i qui ds, and pneumati cs, whi ch i nvol vesgases.Li qui dsandgasesaresi mi l ari nmanyrespects.Thedi fferencesarepoi ntedouti ntheappropri ateareasofthi smanual .Thi smanual presentsmanyofthefunda-mental conceptsi nthefi el dsofhydraul i csandpneumati cs.I ti si ntendedasabasi creferenceforal l personnel oftheNavywhoseduti esandresponsi bi l i ti esrequi rethemtohaveaknowl edgeofthefundamental soffl ui dpower .Conse-quentl y,emphasi si spl acedpri mari l yonthetheory of operati on of typi calfl ui d power systemsand components that have appl i cati ons i n navalequi pment. Many appl i cati ons of fl ui d power arepresented i n thi s manualto i l l ustrate the functi onsandoperati onofdi fferentsystemsandcom-ponents. However, these are onl y representati veof the many appl i cati ons of fl ui d power i n navalequi pment. I ndi vi dualtrai ni ng manual s for eachrate provi de i nformati on concerni ng the appl i ca-ti onoffl ui dpowertospeci fi cequi pmentforwhi ch the rati ng i s responsi bl e.Abr i efsummar yofthecontentsofthi str ai ni ngmanual i sgi veni nthefol l owi ngpar agr aphs:Chapter 2 covers the characteri sti cs of l i qui dsandthefactorsaffecti ngthem.I tal soexpl ai nsthebehavi orofl i qui dsatrest,i denti fi esthecharacteri sti cs of l i qui ds i n moti on, and expl ai nstheoperati onofbasi chydraul i ccomponents.Chapter3di scussesthequal i ti esoffl ui dsacceptabl e for hydraul i c systems and the types offl ui dsused.I ncl udedar esecti onsonsafetyprecauti ons to fol l ow when handl i ng potenti al l yhazar dousfl ui ds,l i qui dcontami nati on,andcontrol ofcontami nants.Chapter4coversthehydraul i cpump,thecomponenti nthehydr aul i csystemwhi chgeneratestheforcerequi redforthesystemtoperformi tsdesi gnfuncti on.Thei nformati onprovi ded covers cl assi fi cati ons, types, operati on,andconstructi onofpumps.Chapter 5 deal s wi th the pi pi ng, tubi ng andfl exi bl ehoses,andconnectorsusedtocarryfl ui dsunder pressure.Chapter 6 di scusses the cl assi fi cati on, types,andoperati onofval vesusedi nthecontrol offl ow,pressure,anddi recti onoffl ui ds.Chapter7coversthetypesandpurposesofseal i ngdevi cesusedi nfl ui dpowersystems,i ncl udi ngthedi fferentmateri al susedi nthei rconstr ucti on.Addi ti onal l y,thegui del i nesforsel ecti ng,i nstal l i ng,andremovi ngO-ri ngsarei ncl uded.Chapter 8 di scusses the operati on of devi cesused to measure and regul ate the pressure of fl ui dsandtomeasurethetemperatureoffl ui ds.Chapter 9 descri bes the functi ons and typesof reservoi rs, strai ners, fi l ters, and accumul ators,and thei r uses i n fl ui d power systems.Chapter 10 di scusses the types and operati onofactuator susedtotr ansfor mtheener gygenerated by hydraul i c systems i nto mechani calforceandmoti on.Chapter 11 deal s wi th pneumati cs. I t di scussesthe ori gi n of pneumati cs, the characteri sti cs andcompressi bi l i ty of gases, and the most commonl yused gases i n pneumati c systems. Al so, secti onsare i ncl uded to cover safety precauti ons and thepotenti al hazardsofcompressedgases.Chapter12i denti fi esthetypesofdi agramsencountered i n fl ui d power systems. Thi s chapteral so di scusses how components of chapters 4, 5,6, 8, 9, and 10 are combi ned to form and operatetogether as a system.Agl ossaryoftermscommonl yusedi nfl ui dpower i spr ovi dedi nappendi xI .Appendi xI Iprovi dessymbol susedi naeronauti cal mechani cal1-1systems, and appendi x I I Iprovi des symbol s usedi nnonaeronauti cal mechani cal systems.The remai nder of chapter 1 i s devoted to theadvantagesandprobl emsoffl ui dpowerappl i -cati ons.I ncl udedarebri efsecti onsonthehi story,devel opment, and appl i cati ons of hydraul i cs,the states of matter.ADVANTAGESOFFLUIDPOWERandThe extensi ve use of hydraul i cs and pneuma-ti cstotransmi tpoweri sduetothefactthatproperl y constructed fl ui d power systems possessanumber offavor abl echar acter i sti cs.Theyel i mi natetheneedforcompl i catedsystemsofgears,cams,andl evers.Moti oncanbetrans-mi ttedwi thoutthesl acki nherenti ntheuseofsol i dmachi neparts.Thefl ui dsusedarenotsubject to breakage as are mechani calparts, andthe mechani sms are not subjected to great wear.Thedi fferentpartsofafl ui dpowersystemcan be conveni entl y l ocated at wi del y separatedpoi nts,si ncetheforcesgeneratedarerapi dl ytransmi tted over consi derabl e di stances wi th smal ll oss. These forces can be conveyed up and downor around corners wi th smal ll oss i n effi ci ency andwi thoutcompl i catedmechani sms.Ver yl ar geforces can be control l ed by much smal l er ones andcan be transmi tted through comparati vel y smal ll i nesandori fi ces.I f the system i s wel ladapted to the work i t i srequi red to perform, and i f i t i s not mi sused, i tcanpr ovi desmooth,fl exi bl e,uni for macti onwi thout vi brati on, and i s unaffected by vari ati onofl oad.I ncaseofanoverl oad,anautomati crel easeofpressurecanbeguaranteed,sothatthesystem i s protected agai nst breakdown or strai n.Fl ui d power systems can provi de wi del y vari abl emoti onsi nbothrotaryandstrai ght-l i netrans-mi ssi on of power. The need for controlby handcanbemi ni mi zed.I naddi ti on,fl ui dpowersystemsareeconomi cal tooperate.The questi on may ari se as to why hydraul i csi s used i n some appl i cati ons and pneumati cs i nothers. Many factors are consi dered by the userand/orthemanufacturerwhendetermi ni ngwhi chtypeofsystemtousei naspeci fi cappl i cati on.Ther ear enohar dandfastr ul estofol l ow;however,pastexperi encehasprovi dedsomesound i deas that are usual l y consi dered when suchdeci si onsaremade.I ftheappl i cati onrequi resspeed,amedi umamountofpressure,andonl yfai rl y accurate control , a pneumati c system maybe used. I f the appl i cati on requi res onl y a medi umamount of pressure and a more accurate control ,a combi nati on of hydraul i cs and pneumati cs maybe used. I f the appl i cati on requi res a great amountof pressure and/or extremel y accurate control , ahydraul i csystemshoul dbeused.SPECIAL PROBLEMSTheextremefl exi bi l i tyoffl ui dpowerel ementspresents a number of probl ems. Si nce fl ui ds havenoshapeofthei rown,theymustbeposi ti vel yconfi nedthroughouttheenti resystem.Speci alconsi derati onmustbegi ventothestructurali ntegri tyofthepartsofafl ui dpowersystem.Strongpi pesandcontai nersmustbeprovi ded.Leaksmustbepr evented.Thi si saser i ousprobl emwi ththehi ghpressureobtai nedi nmanyfl ui dpoweri nstal l ati ons.The operati on of the system i nvol ves constantmovementofthefl ui dwi thi nthel i nesandcomponents.Thi smovementcausesfr i cti onwi thi n the fl ui d i tsel f and agai nst the contai ni ngsurfaces whi ch, i f excessi ve, can l ead to seri ousl osses i n effi ci ency. Forei gn matter must not beal l owed to accumul ate i n the system, where i t wi l lcl og smal lpassages or score cl osel y fi tted parts.Chemi cal acti onmaycausecorrosi on.Anyoneworki ngwi thfl ui dpowersystemsmustknowhowafl ui dpowersystemandi tscomponentsoperate,both i n terms of the generalpri nci pl es commonto al lphysi calmechani sms and of the pecul i ari ti esoftheparti cul ararrangementathand.HYDRAULICSThe wordhydraulicsi sbasedontheGreekword for water, and ori gi nal l y covered the studyof the physi calbehavi or of water at rest and i nmoti on.Usehasbroadenedi tsmeani ngtoi ncl udethe behavi or of al ll i qui ds, al though i t i s pri mari l yconcernedwi ththemoti onofl i qui ds.Hydraul i csi ncl udesthemanneri nwhi chl i qui dsacti ntanksandpi pes,deal swi ththei rproperti es, and expl ores ways to take advantageoftheseproperti es.DEVELOPMENTOFHYDRAULICSAl th ou gh th emoder n dev el opmen tofhydraul i cs i s comparati vel y recent, the anci entswerefami l i arwi thmanyhydraul i cpri nci pl esandthei rappl i cati ons.TheEgypti ansandtheanci entpeopl eofPersi a,I ndi a,andChi naconveyedwater1-2al ongchannel sfor i r r i gati onanddomesti cpurposes, usi ng dams and sl ui ce gates to controlthe fl ow. The anci ent Cretans had an el aboratepl umbi ng system. Archi medes studi ed the l aws offl oati ngandsubmergedbodi es.TheRomansconstructedaqueductstocarrywatertothei rci ti es.After the breakup of the anci ent worl d, therewere few new devel opments for many centuri es.Then,over acompar ati vel yshor tper i od,begi nni ng near the end of the seventeenth century,I tal i anphysi ci st,Evangel i staTorri cel l e,Frenchphysi ci st,EdmeMar i otte,andl ater ,Dani elBernoul l i conductedexperi mentstostudytheel ementsoffor cei nthedi schar geofwaterthrough smal lopeni ngs i n the si des of tanks andthroughshortpi pes.Duri ngthesameperi od,Bl ai se Pascal , a French sci enti st, di scovered thefundamental l awforthesci enceofhydraul i cs.Pascal s l aw states that i ncrease i n pressure onthesurfaceofaconfi nedfl ui di stransmi ttedundi mi ni shed throughout the confi ni ng vesselorsystem(fi g.1-1).(Thi si sthebasi cpri nci pl eofhydraul i cs and i s covered i n detai li n chapter 2ofthi smanual .)ForPascal sl awtobemadeeffecti veforpracti calappl i cati ons, i t was necessary to have api ston that fi t exactl y. I t was not unti lthe l atterpart of the ei ghteenth century that methods werefound to make these snugl y fi tted parts requi redi n hydraul i c systems. Thi s was accompl i shed bythe i nventi on of machi nes that were used to cutand shape the necessary cl osel y fi tted parts and,parti cul arl y, by the devel opment of gaskets andpacki ngs.Si ncethatti me,componentssuchasval ves,pumps,actuati ngcyl i nders,andmotorshavebeendevel opedandr efi nedtomak ehydraul i cs one of the l eadi ng methods of trans-mi tti ngpower.Figure 1-1.Force transmitted through fluid.Use of HydraulicsThe hydraul i c press, i nvented by Engl i shmanJohnBr ahmah,wasoneofthefi r stwor k-abl epi ecesofmachi nerydevel opedthatusedhydraul i csi ni tsoperati on.I tconsi stedofapl unger pump pi ped to a l arge cyl i nder and a ram.Thi s press found wi de use i n Engl and because i tprovi ded a more effecti ve and economi calmeansofappl yi ngl argeforcesi ni ndustri al uses.Today,hydraul i cpoweri susedtooperatemanydi ffer enttool sandmechani sms.I nagarage,amechani crai sestheendofanauto-mobi l e wi th a hydraul i c jack. Denti sts and barbersuse hydraul i c power, through a few strokes of acontroll ever, to l i ft and posi ti on thei r chai rs toaconveni entworki nghei ght.Hydraul i cdoorstopskeepheavydoor sfr omsl ammi ng.Hydr aul i cbrakeshavebeenstandardequi pmentonauto-mobi l essi ncethe1930s.Mostautomobi l esareequi pped wi th automati c transmi ssi ons that arehydraul i cal l yoperated.Powersteeri ngi sanotherappl i cati onofhydr aul i cpower .Constr ucti onworkersdependuponhydraul i cpowerfortheoper ati onofvar i ouscomponentsofthei requi pment. For exampl e, the bl ade of a bul l dozeri snormal l yoperatedbyhydraul i cpower.Duri ngtheperi odprecedi ngWorl dWarI I ,theNavybegantoappl yhydraul i cstonavalmechani smsextensi vel y.Si ncethen,navalappl i cati onshavei ncreasedtothepoi ntwheremany i ngeni ous hydraul i c devi ces are used i n thesol uti on of probl ems of gunnery, aeronauti cs, andnavi gati on. Aboard shi p, hydraul i c power i s usedto operate such equi pment as anchor wi ndl asses,cranes, steeri ng gear, remote controldevi ces, andpower dri ves for el evati ng and trai ni ng guns androcket l aunchers. El evators on ai rcraft carri ers usehydraul i cpowertotransferai rcraftfromthehangardecktothefl i ghtdeckandvi ceversa.Hydraul i cs and pneumati cs (chapter 11) arecombi nedforsomeappl i cati ons.Thi scombi na-ti oni sreferredtoashydropneumati cs.A nexampl eofthi scombi nati oni sthel i ftusedi ngaragesandservi cestati ons.Ai rpressurei sappl i edtothesurfaceofhydraul i cfl ui di nareservoi r.Theai rpressureforcesthehydraul i cfl ui d to rai se the l i ft.STATES OF MATTERThe materi althat makes up the uni verse i sknownasmatter.Matter i sdefi nedasanysubstancethatoccupi esspaceandhaswei ght.1-3Matter exi sts i n three states: sol i d, l i qui d, and gas;each has di sti ngui shi ng characteri sti cs. Sol i ds haveadefi ni tevol umeandadefi ni teshape;l i qui dshave a defi ni te vol ume, but take the shape of thei rcontai ni ng vessel s; gases have nei ther a defi ni teshape nor a defi ni te vol ume. Gases not onl y takethe shape of the contai ni ng vessel , but al so expandandfi l l thevessel ,regardl essofi tsvol ume.Exampl es of the states of matter are i ron, water,and ai r.Matter can change from one state to another.Water i s a good exampl e. At hi gh temperaturesi ti si nthegaseousstateknownassteam.Atmoderate temperatures i t i s a l i qui d, and at l owtemperaturesi tbecomesi ce,whi chi sdefi ni tel ya sol i d state. I n thi s exampl e, the temperature i sthe domi nant factor i n determi ni ng the state thesubstance assumes.Pressure i s another i mportant factor that wi l laffect changes i n the state of matter. At pressuresl ower than atmospheri c pressure, water wi l lboi land thus change i nto steam at temperatures l owerthan 212 Fahrenhei t (F). Pressure i s al so a cri ti calfactor i n changi ng some gases to l i qui ds or sol i ds.Normal l y,whenpressureandchi l l i ngarebothappl i ed to a gas, the gas assumes a l i qui d state.Li qui dai r,whi chi sami xtureofoxygenandni trogen,i sproducedi nthi smanner.I n the study of fl ui d power, we are concernedpri mari l y wi th the properti es and characteri sti csof l i qui ds and gases. However, you shoul d keepi nmi ndthattheproperti esofsol i dsal soaffectthe characteri sti cs of l i qui ds and gases. The l i nesandcomponents,whi charesol i ds,encl oseandcontr ol thel i qui dor gasi nthei r r especti vesystems.1-4CHAPTER 2FORCES IN LIQUIDSThe study of l i qui ds i s di vi ded i nto two mai nparts: l i qui ds at rest (hydrostati cs) and l i qui ds i nmoti on(hydraul i cs).Theeffectsofl i qui dsatr estcanoftenbeexpressedbysi mpl eformul as.Theeffectsofl i qui dsi nmoti onar emor edi ffi cul ttoexpr essduetofr i cti onal andother factor swhoseacti onscannotbeexpressedbysi mpl emathemati cs.I n chapter 1 we l earned that l i qui ds have adefi ni tevol umebuttaketheshapeofthei rcontai ni ngvessel . Ther ear etwoaddi ti onalcharacteri sti cswemustexpl orepri ortopro-ceedi ng.Li qui dsar eal mosti ncompr essi bl e.Forexampl e, i f a pressure of 100 pounds per squarei nch (psi ) i s appl i ed to a gi ven vol ume of waterthat i s at atmospheri c pressure, the vol ume wi l ldecreasebyonl y0.03percent.I twoul dtakeaforceofapproxi matel y32tonstoreducei tsvol ume by 10 percent; however, when thi s forcei s removed, the water i mmedi atel y returns to i tsori gi nal vol ume.Otherl i qui dsbehavei naboutthe same manner as water.Another char acter i sti cofal i qui di sthetendencytokeepi tsfreesurfacel evel .I fthesurfacei snotl evel ,l i qui dswi l l fl owi nthedi recti onwhi chwi l l tendtomakethesurfacel evel .LIQUIDS AT RESTI nstudyi ngfl ui dsatr est,wear econ-cer nedwi ththetr ansmi ssi onoffor ceandthefactorswhi chaffecttheforcesi nl i qui ds.Addi ti onal l y,pressurei nandonl i qui dsandfactor saffecti ngpr essur ear eofgr eati m-portance.PRESSURE AND FORCETheter msforceandpressurear eu s edextensi vel yi nthestudyoffl ui dpower .I ti sessenti al thatwedi sti ngui shbetweentheter ms.For cemeansatotal pushor pul l .I ti sthepushor pul l exer tedagai nstthetotalarea of a parti cul ar surface and i s expressedi n pounds or grams. Pressure means the amountof push or pul l(force) appl i ed to each uni t areaofthesurfaceandi sexpressedi npoundspers qu ar ei n ch (l b/i n2)or gr amsper squar ecenti meter(gm/cm2). Pressure maybe exerted i nonedi recti on,i nseveral di recti ons,ori nal ldi recti ons.Computing Force, Pressure, and AreaAfor mul ai susedi ncomputi ngfor ce,pressure,andareai nfl ui dpowersystems.I nthi sformul a, P refers to pressure, F i ndi cates force,and A represents area.Forceequal spressureti mesarea.Thus,theformul a i s wri ttenEquati on2-1.Pressureequal sforcedi vi dedbyarea.Byrearrangi ng the formul a, thi s statement may becondensedi ntoEquati on2-2.Si nce area equal s force di vi ded by pressure,the formul a i s wri ttenEquati on2-3.2-1Figure 2-1.Device for determining the arrangement of theforce, pressure, and area formula.Fi gure2-1i l l ustratesamemorydevi ceforrecal l i ng the di fferent vari ati ons of thi s formul a.Any l etter i n the tri angl e may be expressed as theproduct or quoti ent of the other two, dependi ngoni tsposi ti onwi thi nthetri angl e.For exampl e, to fi nd area, consi der the l etterA as bei ng set off to i tsel f, fol l owed by an equalsi gn. Now l ook at the other two l etters. The l etterFi sabovethel etterP;therefore,NOTE:Someti mesthear eamaynotbeexpr essedi nsquar euni ts.I fthesur facei sr ectangul ar ,youcandeter mi nei tsar eabymul ti pl yi ng i ts l ength (say, i n i nches) by i ts wi dth(al soi ni nches).Themajori tyofareasyouwi l lconsi der i n these cal cul ati ons are ci rcul ar i n shape.Ei ther the radi us or the di ameter may be gi ven,but you must know the radi us i n i nches to fi ndthe area. The radi us i s one-hal f the di ameter. Todetermi ne the area, use the formul a for fi ndi ngthe area of a ci rcl e. Thi s i s wri tten A = whereA i s the area, i s 3.1416 (3.14 or 3 1/7 for mostcal cul ati ons), and r2 i ndi cates the radi us squared.AtmosphericPressureThe atmosphere i s the enti re mass of ai r thatsurrounds the earth. Whi l e i t extends upward forabout 500 mi l es, the secti on of pri mary i nteresti s the porti on that rests on the earths surface andextends upward for about 7 1/2 mi l es. Thi s l ayeri s cal l ed the troposphere.I f a col umn of ai r 1-i nch square extendi ng al lthewaytothetopoftheatmospherecoul dbewei ghed,thi scol umnofai rwoul dwei ghapproxi matel y14.7poundsatseal evel .Thus,atmospheri c pressure at sea l eveli s approxi matel y14.7 psi .Asoneascends,theatmospheri cpressuredecreases by approxi matel y 1.0 psifor every 2,343feet.However,bel owseal evel ,i nexcavati onsanddepressi ons, atmospheri cpressurei ncreases.Pressuresunderwaterdi fferfromthoseunderai ronl ybecausethewei ghtofthewatermustbeadded to the pressure of the ai r.Atmospheri cpressurecanbemeasuredbyanyofsever al methods.Thecommonl abor ator ymethod uses the mercury col umn barometer. Thehei ghtofthemer cur ycol umnser vesasani ndi cator of atmospheri c pressure. At sea l evelandat a temperature of 0 Cel si us (C), the hei ght ofthe mercury col umn i s approxi matel y 30 i nches,or 76 centi meters. Thi s represents a pressure ofapproxi matel y14.7psi .The30-i nchcol umni sused as a reference standard.Another devi ce used to measure atmospheri cpressurei stheaneroi dbarometer.Theaneroi dbar ometer usesthechangei nshapeofanevacuatedmetal cel l tomeasurevari ati onsi natmospheri c pressure (fi g. 2-2). The thi n metalofthe aneroi d cel lmoves i n or out wi th the vari ati onof pressure on i ts externalsurface. Thi s movementi stransmi ttedthroughasystemofl everstoapoi nter,whi chi ndi catesthepressure.Theatmospher i cpr essur edoesnotvar yuni forml y wi th al ti tude. I t changes more rapi dl yat l ower al ti tudes because of the compressi bi l i tyof the ai r, whi ch causes the ai r l ayers cl ose to theearths surface to be compressed by the ai r massesabovethem.Thi seffect,however,i sparti al l ycounteractedbythecontracti onoftheupperFigure 2-2.Simple diagram of the aneroid barometer.2-2l ayer sduetocool i ng.Thecool i ngtendstoi ncrease the densi ty of the ai r.Atmospheri c pressures are qui te l arge, but i nmosti nstancespracti cal l ythesamepressurei spresentonal l si desofobjectssothatnosi ngl esurfacei ssubjectedtoagreatl oad.Atmospheri c pressure acti ng on the surface ofa l i qui d (fi g. 2-3, vi ew A) i s transmi tted equal l ythroughout the l i qui d to the wal l s of the contai ner,buti sbal ancedbythesameatmospheri cpressureacti ng on the outer wal l s of the contai ner. I n vi ewBoffi gure2-3,atmospheri cpressureacti ngonthe surface of one pi ston i s bal anced by the samepressureacti ngonthesurfaceoftheotherpi ston.The di fferent areas of the two surfaces make nodi fference, si nce for a uni t of area, pressures arebal anced.TRANSMISSION OF FORCESTHROUGHLIQUIDSWhen the end of a sol i d bar i s struck, the mai nforce of the bl ow i s carri ed strai ght through thebartotheotherend(fi g.2-4,vi ewA).Thi shappensbecausethebari sri gi d.Thedi recti onofthebl owal mostenti r el ydeter mi nesthedi recti on of the transmi tted force. The more ri gi dFigure 2-4.Transmission of force: (A) solid; (B) fluid.thebar,thel essforcei sl osti nsi dethebarortr ansmi ttedoutwar datr i ghtangl estothedi recti onofthebl ow.When a force i s appl i ed to the end of a col umnofconfi nedl i qui d(fi g.2-4,vi ewB),i ti stransmi tted strai ght through to the other end andal so equal l y and undi mi ni shed i n every di recti onthroughout the col umnforward, backward, andsi dewaysso that the contai ni ng vesseli s l i teral l yfi l l ed wi th pressure.Anexampl eofthi sdi stri buti onofforcei si l l ustrated i n fi gure 2-5. The fl at hose takes onFigure 2-3.Effects of atmospheric pressure. Figure 2-5.Distribution of force.2-3a ci rcul ar cross secti on when i t i s fi l l ed wi th waterunder pressure. The outward push of the wateri sequal i neverydi recti on.Sofar wehaveexpl ai nedtheeffectsofatmospheri cpressureonl i qui dsandhowexternalforces are di stri buted through l i qui ds. Let us nowfocusourattenti ononforcesgeneratedbythewei ght of l i qui ds themsel ves. To do thi s, we mustfi rst di scuss densi ty, speci fi c gravi ty, and Pascal sl aw.Density and Specific GravityThe densi ty of a substance i s i ts wei ght per uni tvol ume.Theuni tvol umei ntheEngl i shsystemofmeasurementi s1cubi cfoot.I nthemetri csystem i t i s the cubi c centi meter; therefore, densi tyi s expressed i n pounds per cubi c foot or i n gramspercubi ccenti meter.To fi nd the densi ty of a substance, you mustknow i ts wei ght and vol ume. You then di vi de i tswei ght by i ts vol ume to fi nd the wei ght per uni tvol ume.I nequati onform,thi si swri ttenasEquati on2-4.EXAMPLE: The l i qui d that fi l l s a certai ncontai ner wei ghs1,497.6pounds.Thecontai neri s4feetl ong,3feetwi de,and2feetdeep.I tsvol umei s24cubi cfeet(4 ft x 3 ft x 2 ft). I f 24 cubi c feet of thi sl i qui d wei ghs 1,497.6 pounds, then 1 cubi cfootwei ghsor62.4pounds.Therefore,thedensi tyofthel i qui di s62.4poundspercubi cfoot.Thi si sthedensi tyofwaterat4Candi susual l yusedasthestandar dfor compar i ngdensi ti es of other substances. The temperature of4C was sel ected because water has i ts maxi mumdensi tyatthi stemperature.I nthemetri csystem,thedensi tyofwater i s1gr amper cubi ccenti meter. The standard temperature of 4C i sused whenever the densi ty of l i qui ds and sol i dsi smeasured.Changesi ntemperaturewi l l notchange the wei ght of a substance but wi l lchangethevol umeofthesubstancebyexpansi onorcontracti on,thuschangi ngthewei ghtperuni tvol ume.I n physi cs, the word specifici mpl i esarati o.Wei ght i s the measure of the earths attracti on fora body. The earths attracti on for a body i s cal l edgravi ty.Thus,therati oofthewei ghtofauni tvol umeofsomesubstancetothewei ghtofanequalvol ume of a standard substance, measuredunderstandardpressureandtemperaturecon-di ti ons,i scal l edspeci fi cgr avi ty.Theter msspecific weight and specific density are someti mesused to express thi s rati o.Thefol l owi ngformul asareusedtofi ndthespeci fi c gravi ty (sp gr) of sol i ds and l i qui ds, wi thwater used as the standard substance.or ,The same formul as are used to fi nd the speci fi cgravi tyofgasesbysubsti tuti ngai r,oxygen,orhydrogenforwater.I facubi cfootofacertai nl i qui dwei ghs68.64pounds,theni tsspeci fi cgravi tyi s1.1,Thus, the speci fi c gravi ty of the l i qui d i s therati o of i ts densi ty to the densi ty of water. I f thespeci fi c gravi ty of a l i qui d or sol i d i s known, thedensi ty of the l i qui d or sol i d maybe obtai ned bymul ti pl yi ng i ts speci fi c gravi ty by the densi ty ofwater. For exampl e, i f a certai n hydraul i c l i qui dhasaspeci fi cgravi tyof0.8,1cubi cfootofthel i qui d wei ghs 0.8 ti mes as much as a cubi c footof water0.8 ti mes 62.4, or 49.92 pounds. I n themetri c system, 1 cubi c centi meter of a substancewi th a speci fi c gravi ty of 0.8 wei ghs 1 ti mes 0.8,or 0.8 grams. (Note that i n the metri c system thespeci fi c gravi ty of a l i qui d or sol i d has the samenumeri cal val ueasi tsdensi ty,becausewaterwei ghs1grampercubi ccenti meter.)Speci fi c gravi ty and densi ty are i ndependentof the si ze of the sampl e under consi derati on anddepend onl y on the substance of whi ch i t i s made.Adevi cecal l edahydrometeri susedformeasuri ngthespeci fi cgravi tyofl i qui ds.2-4PascalsLawRecal lfrom chapter 1 that the foundati on ofmodern hydraul i cs was establ i shed when Pascaldi scovered that pressure i n a fl ui d acts equal l y i nal ldi recti ons. Thi s pressure acts at ri ght angl estothecontai ni ngsur faces.I fsometypeofpressuregauge,wi thanexposedface,i spl acedbeneaththesurfaceofal i qui d(fi g.2-6)ataspeci fi c depth and poi nted i n di fferent di recti ons,the pressure wi l lread the same. Thus, we can saythatpr essur ei nal i qui di si ndependentofdi recti on.Pressure due to the wei ght of a l i qui d, at anyl evel , depends on the depth of the fl ui d from thesurface. I f the exposed face of the pressure gauges,fi gure 2-6, are moved cl oser to the surface of thel i qui d, the i ndi cated pressure wi l lbe l ess. Whenthedepthi sdoubl ed,thei ndi catedpressurei sdoubl ed. Thus the pressure i n a l i qui d i s di rectl yproporti onal tothedepth.Consi der acontai ner wi thver ti cal si des(fi g. 2-7) that i s 1 foot l ong and 1 foot wi de. Leti tbefi l l edwi thwater1footdeep,provi di ng1cubi cfootofwater.Wel earnedearl i eri nthi schapterthat1cubi cfootofwaterwei ghs62.4pounds. Usi ng thi s i nformati on and equati on 2-2,P=F/A,wecancal cul atethepressureonthebottomofthecontai ner.Si nce there are 144 square i nches i n 1 square foot,Thi scanbestatedasfol l ows:thewei ghtofacol umnofwater1foothi gh,havi ngacross-secti onalarea of 1 square i nch, i s 0.433 pound.I fthedepthofthecol umni stri pl ed,thewei ght of the col umn wi l lbe 3 x 0.433, or 1.299pounds,andthepressureatthebottomwi l l be1.299l b/i n2 (psi ), si nce pressure equal s the forcedi vi dedbythearea.Thus,thepressureatanydepthi nal i qui di sequal tothewei ghtofthecol umnofl i qui datthatdepthdi vi dedbytheFigure 2-6.Pressure of a liquid is independent of direction.cross-secti onalarea of the col umn at that depth.Thevol umeofal i qui dthatproducesthepressurei s referred to as the fl ui d head of the l i qui d. Thepressure of a l i qui d due to i ts fl ui d head i s al sodependentonthedensi tyofthel i qui d.I f we l et A equalany cross-secti onalarea ofal i qui dcol umnandhequal thedepthofthecol umn, the vol ume becomes Ah. Usi ng equati on2-4, D = W/V, the wei ght of the l i qui d above areaAi sequal toAhD.Figure 2-7.Water pressure in a 1-cubic-foot container.2-5Si nce pressure i s equalto the force per uni t area,setAequal to1.Thentheformul apressurebecomesP = h D Equati on2-5.I t i s essenti althat h and D be expressed i n si mi l aruni ts.Thati s,i fDi sexpressedi npoundspercubi cfoot,theval ueofhmustbeexpressedi nfeet. I f the desi red pressure i s to be expressed i npoundspersquarei nch,thepressureformul a,equati on2-5,becomesEquati on2-6.Pas cal was al s oth efi r s ttopr ov ebyexper i mentthattheshapeandvol umeofacontai ner i n no way al ters pressure. Thus i n fi gure2-8, i f the pressure due to the wei ght of the l i qui datapoi ntonhori zontal l i neHi s8psi ,thepressurei s8psi everywhereatl evel Hi nthesystem. Equati on 2-5 al so shows that the pressurei si ndependentoftheshapeandvol umeofacontai ner.Pressure and Force in Fluid Power SystemsFigure 2-9.Force transmitted through fluid.of the shape of the contai ner. Consi der the effectof thi s i n the system shown i n fi gure 2-9. I f therei s a resi stance on the output pi ston and the i nputpi ston i s pushed downward, a pressure i s createdthroughthefl ui d,whi chactsequal l yatri ghtangl estosurfacesi nal l partsofthecontai ner.I f force 1 i s 100 pounds and the area of thei nput pi ston i s 10 square i nches, then the pressurei n the fl ui d i s 10 psiRecal l that,accordi ngtoPascal sl aw,anyforceappl i edtoaconfi nedfl ui di stransmi ttedi n al ldi recti ons throughout the fl ui d regardl essNOTE:Fl ui dpressurecannotbecreatedwi thoutresi stancetofl ow.I nthi scase,resi stanceFigure2-8.Pressurerelationship2-6withshape.i spr ovi dedbytheequi pmenttowhi chtheoutputpi stoni sattached.Thefor ceofr e-si stanceactsagai nstthetopoftheoutputpi ston.Thepr essur ecr eatedi nthesystembythei nputpi stonpushesontheundersi deoftheoutputpi stonwi thaforceof10poundsoneachsquarei nch.I n thi s case, the fl ui d col umn has a uni formcrosssecti on,sotheareaoftheoutputpi stoni sthesameastheareaofthei nputpi ston,or 10squar ei nches. Ther efor e,theupwar dfor ceontheoutputpi stoni s100pounds(10 psix 10 sq. i n.), the same as the force appl i edto the i nput pi ston. Al lthat was accompl i shed i nthi s system was to transmi t the 100-pound forcearound the bend. However, thi s pri nci pl e under-l i espracti cal l yal l mechani cal appl i cati onsoffl ui dpower.Atthi spoi ntyoushoul dnotethatsi ncePascal sl awi si ndependentoftheshapeofthecontai ner ,i ti snotnecessar ythatthetubeconnecti ngthetwopi stonshavethesamecross-secti onalarea of the pi stons. A connecti onof any si ze, shape, or l ength wi l ldo, as l ong asan unobstructed passage i s provi ded. Therefore,the system shown i n fi gure 2-10, wi th a rel ati vel ysmal l ,bentpi peconnecti ngtwocyl i nder s,wi l lact exactl y the same as the system shown i nfi gure2-9.MULTIPLICATIONOFFORCES.Con-si derthesi tuati oni nfi gure2-11,wherethei nputpi stoni smuchsmal l erthantheoutputpi ston.Assumethattheareaofthei nputpi stoni s2square i nches. Wi th a resi stant force on the outputpi ston a downward force of 20 pounds acti ng onthe i nput pi ston creates a pressure of or 10 psiFigure 2-10.Transmitting force through a small pipe.Figure2-11.Multiplicationofforces.i n the fl ui d. Al though thi s force i s much smal l erthan the force appl i ed i n fi gures 2-9 and 2-10, thepressure i s the same. Thi s i s because the force i sappl i ed to a smal l er area.Thi s pressure of 10 psiacts on al lparts of thefl ui dcontai ner ,i ncl udi ngthebottomoftheoutputpi ston.Theupwardforceontheoutputpi ston i s 200 pounds (10 pounds of pressure oneach square i nch). I n thi s case, the ori gi nalforcehas been mul ti pl i ed tenfol d whi l e usi ng the samepressure i n the fl ui d as before. I n any system wi ththesedi mensi ons,therati oofoutputforcetoi nput force i s al ways ten to one, regardl ess of theappl i edforce.Forexampl e,i ftheappl i edforceof the i nput pi ston i s 50 pounds, the pressure i nthesystemwi l l be25psi .Thi swi l l supportaresi stant force of 500 pounds on the output pi ston.The system works the same i n reverse. I f wechange the appl i ed force and pl ace a 200-poundforceontheoutputpi ston(fi g.2-11),maki ngi tthei nputpi ston,theoutputforceonthei nputpi stonwi l l beone-tenththei nputforce,or20pounds.(Someti messuchresul tsaredesi red.)Therefore,i ftwopi stonsareusedi nafl ui dpowersystem, the force acti ng on each pi ston i s di rectl yproporti onal toi tsarea,andthemagni tudeofeach force i s the product of the pressure and theareaofeachpi ston.Note the whi te arrows at the bottom of fi gure2-11 that i ndi cate up and down movement. Themovement they represent wi l lbe expl ai ned l ateri n the di scussi on of vol ume and di stance factors.2-7DIFFERENTIALAREAS.Consi derthespeci al si tuati onshowni nfi gure2-12.Here,asi ngl e pi ston (1) i n a cyl i nder (2) has a pi ston rod(3)attachedtooneofi tssi des.Thepi stonrodextends out of one end of the cyl i nder. Fl ui d underpressure i s admi tted equal l y to both ends of thecyl i nder.Theopposedfacesofthepi ston(1)behavel i ketwopi stonsacti ngagai nsteachother.The area of one face i s the ful lcross-secti onalareaof the cyl i nder, say 6 square i nches, whi l e the areaof the other face i s the area of the cyl i nder mi nustheareaofthepi stonrod,whi chi s2squarei nches. Thi s l eaves an effecti ve area of 4 squarei nches on the ri ght face of the pi ston. The pressureonbothfacesi sthesame,i nthi scase,20psi .Appl yi ng the rul e just stated, the force pushi ngthe pi ston to the ri ght i s i ts area ti mes the pressure,or 120pounds(20x6).Li kewi se,thefor cepushi ng the pi ston to the l eft i s i ts area ti mes thepressure, or 80 pounds (20 x 4). Therefore, therei s a net unbal anced force of 40 pounds acti ng tother i ght,andthepi stonwi l l movei nthatdi recti on. The net effect i s the same as i f the pi stonand the cyl i nder had the same cross-secti onalareaasthepi stonrod.VOLUMEANDDISTANCEFACTORS.You have l earned that i f a force i s appl i ed to asystem and the cross-secti onalareas of the i nputand output pi stons are equal , as i n fi gures 2-9 and2-10,theforceonthei nputpi stonwi l l supportan equalresi stant force on the output pi ston. Thepressure of the l i qui d at thi s poi nt i s equalto theforce appl i ed to the i nput pi ston di vi ded by thepi stons area. Let us now l ook at what happenswhen a force greater than the resi stance i s appl i edtothei nputpi ston.I n the system i l l ustrated i n fi gure 2-9, assumethat the resi stance force on the output pi ston i s100 psi . I f a force sl i ghtl y greater than 100 poundsi s appl i ed to the i nput pi ston, the pressure i n thesystem wi l lbe sl i ghtl y greater than 10 psi . Thi si ncrease i n pressure wi l lovercome the resi stanceforceontheoutputpi ston.Assumethatthei nputpi ston i s forced downward 1 i nch. The movementdi spl aces 10 cubi c i nches of fl ui d. The fl ui d mustgo somewhere. Si nce the system i s cl osed and thefl ui d i s practi cal l y i ncompressi bl e, the fl ui d wi l lmove to the ri ght si de of the system. Because theoutputpi stonal sohasacross-secti onal areaof10 square i nches, i t wi l lmove 1 i nch upward toaccommodatethe10cubi ci nchesoffl ui d.Youmay general i ze thi s by sayi ng that i f two pi stonsi n a cl osed system have equalcross-secti onalareasandonepi stoni spushedandmoved,theotherpi stonwi l l movethesamedi stance,thoughi ntheopposi te di recti on. Thi s i s because a decrease i nvol ume i n one part of the system i s bal anced byone equali ncrease i n vol ume i n another part ofthe system.Appl y thi s reasoni ng to the system i n fi gure2-11. I f the i nput pi ston i s pushed down a di stanceFigure 2-12.Differential areas on a piston.2-8of 1 i nch, the vol ume of fl ui d i n the l eft cyl i nderwi l ldecrease by 2 cubi c i nches. At the same ti me,the vol ume i n the ri ght cyl i nder wi l li ncrease by2cubi ci nches.Si ncethedi ameteroftheri ghtcyl i ndercannotchange,thepi stonmustmoveupwardtoal l owthevol umetoi ncrease.Thepi ston wi l lmove a di stance equalto the vol umei ncrease di vi ded by the surface area of the pi ston(equalto the surface area of the cyl i nder). I n thi sexampl e, the pi ston wi l lmove one-tenth of an i nch(2 cu. i n. 20 sq. i n.). Thi s l eads to the secondbasi c rul e for a fl ui d power system that contai nstwo pi stons: The di stances the pi stons move arei nversel y proporti onalto the areas of the pi stons.Or more si mpl y, i f one pi ston i s smal l er than theother,thesmal l erpi stonmustmoveagreaterdi stance than the l arger pi ston any ti me the pi stonsmove.LIQUIDSINMOTIONI n the operati on of fl ui d power systems, theremust be a fl ow of fl ui d. The amount of fl ow wi l lvary from system to system. To understand fl ui dpower systemsi nacti on,i ti snecessar ytounderstand some of the characteri sti cs of l i qui dsi nmoti on.Li qui dsi nmoti onhavecharacteri sti csdi f-ferent from l i qui ds at rest. Fri cti onalresi stanceswi thi n a fl ui d (vi scosi ty) and i nerti a contri bute tothese di fferences. (Vi scosi ty i s di scussed i n chapter3.) I nertia,whi chmeanstheresi stanceamassofferstobei ngseti nmoti on,wi l l bedi scussedl ateri nthi ssecti on.Thereareotherrel ati onshi psof l i qui ds i n moti on wi th whi ch you must becomefami l i ar.Amongthesearevol umeandvel oci tyoffl ow,fl owr ateandspeed,l ami nar andturbul entfl ow,andmorei mportantl y,theforceandenergychangeswhi choccuri nfl ow.VOLUMEANDVELOCITYOFFLOWThevol umeofal i qui dpassi ngapoi nti nagi ven ti me i s known as i ts volume of flow or fl owrate. The vol ume of fl ow i s usual l y expressed i ngal l ons per mi nute (gpm) and i s associ ated wi threl ati ve pressures of the l i qui d, such as 5 gpm at40 psi .Thevelocityoffloworvel oci tyofthefl ui di s defi ned as the average speed at whi ch the fl ui dmoves past a gi ven poi nt. I t i s usual l y expressedi n feet per second (fps) or feet per mi nute (fpm).Vel oci ty of fl ow i s an i mportant consi derati on i nsi zi ngthehydraul i cl i nes.(Hydraul i cl i nesaredi scussedi nchapter5.)Vol umeandvel oci tyoffl owar eoftenconsi der edtogether . Wi thother condi ti onsunal ter edthati s, wi th v ol u meofi n pu tunchangedthe vel oci ty of fl ow i ncreases as thecrosssecti onorsi zeofthepi pedecreases,andthevel oci tyoffl owdecreasesasthecrosssecti oni ncreases. For exampl e, the vel oci ty of fl ow i s sl owatwi departsofastreamandrapi datnarrowparts, yet the vol ume of water passi ng each partof the stream i s the same.I nfi gure2-13,i fthecross-secti onal areaofthepi pei s16squarei nchesatpoi ntAand4squarei nchesatpoi ntB,wecancal cul atetherel ati ve vel oci ty of fl ow usi ng the fl ow equati onQ = v A Equati on2-7.where Q i s the vol ume of fl ow, v i s the vel oci tyoffl owandAi sthecross-secti onal areaofthel i qui d.Si ncethevol umeoffl owatpoi ntA,Q1,i s equalto the vol ume of fl ow at poi nt B, Q2, wecan use equati on 2-7 to determi ne the rati o of theFigure 2-13.Volume and velocity of flow.2-9vel oci tyoffl owatpoi ntA,v1,tothevel oci tyoffl owatpoi ntB,v2.Si n ceQ1 =Q2,A1v1 =A2v2Fromfi gure2-13;A1 =16sq.i n.,A2 =4sq.i n.Substi tuti ng:16v1 =4V2 orv2 =4vITherefore, the vel oci ty of fl ow at poi nt B i s fourti mesthevel oci tyoffl owatpoi ntA.VOLUMEOFFLOWANDSPEEDI f you consi der the cyl i nder vol ume you mustfi l land the di stance the pi ston must travel , youcan rel ate the vol ume of fl ow to the speed of thepi ston.Thevol umeofthecyl i nderi sfoundbymul ti pl yi ng the pi ston area by the l ength the pi stonmusttravel (stroke).Supposeyouhavedeter mi nedthattwocyl i ndershavethesamevol umeandthatonecyl i nder i s twi ce as l ong as the other. I n thi s case,the cross-secti onalarea of the l onger tube wi l lbehal f of the cross-secti onalarea of the other tube.I f fl ui d i s pumped i nto each cyl i nder at the samerate, both pi stons wi l lreach thei r ful ltravelat thesameti me.However,thepi stoni nthesmal l ercyl i nder must traveltwi ce as fast because i t hastwi ceasfartogo.There are two ways of control l i ng the speedof the pi ston, (1) by varyi ng the si ze of the cyl i nderand(2)byvaryi ngthevol umeoffl ow(gpm)tothe cyl i nders. (Hydraul i c cyl i nders are di scussedi n detai li n chapter 10. )STREAMLINEANDTURBULENTFLOWAt l ow vel oci ti es or i n tubes of smal ldi ameter,fl owi sstreaml i ned.Thi smeansthatagi venparti cl e of fl ui d moves strai ght forward wi thoutbumpi ngi ntootherparti cl esandwi thoutcrossi ngthei r paths. Streaml i ne fl ow i s often referred toasl ami narfl ow,whi chi sdefi nedasafl owsi tuati on i n whi ch fl ui d moves i n paral l ell ami naorl ayers.Asanexampl eofstreaml i nefl ow,consi derfi gure2-14,whi chi l l ustratesanopenstream fl owi ng at a sl ow, uni form rate wi th l ogsfl oati ng on i ts surface. The l ogs represent parti cl esoffl ui d.Asl ongasthestreamfl owsatasl ow,uni formrate,eachl ogfl oatsdownstreami ni tsFigure 2-14.Streamline flow.own path, wi thout crossi ng or bumpi ng i nto theother.I fthestreamnarrows,however,andthevol umeoffl owremai nsthesame,thevel oci tyoffl owi ncr eases.I fthevel oci tyi ncr easessuffi ci entl y,thewaterbecomesturbul ent.(Seefi g.2-15.)Swi rl s,eddi es,andcross-moti onsareset up i n the water. As thi s happens, the l ogs arethrown agai nst each other and agai nst the banksofthestream,andthepathsfol l owedbydi fferentl ogswi l l crossandrecross.Parti cl es of fl ui d fl owi ng i n pi pes act i n thesame manner. The fl ow i s streaml i ned i f the fl ui dfl ows sl owl y enough, and remai ns streaml i ned atgreatervel oci ti esi fthedi ameterofthepi pei ssmal l .I fthevel oci tyoffl oworsi zeofpi pei si ncreasedsuffi ci entl y,thefl owbecomesturbul ent.Whi l eahi ghvel oci tyoffl owwi l l produceturbul ence i n any pi pe, other factors contri buteto turbul ence. Among these are the roughness ofthe i nsi de of the pi pe, obstructi ons, the degree ofcurvature of bends, and the number of bends i nthepi pe.I nsetti ngupormai ntai ni ngfl ui dpowersystems,careshoul dbetakentoel i mi nateorFigure 2-15.Turbulent flow.2-10mi ni mi zeasmanycausesoftur bul enceaspossi bl e,si ncetheenergyconsumedbyturbul encei swasted.Li mi tati onsrel atedtothedegreeandnumberofbendsofpi pearedi scussedi nchapter 5.Whi l e desi gners of fl ui d power equi pment dowhat they can to mi ni mi ze turbul ence, i t cannotbe avoi ded. For exampl e, i n a 4-i nch pi pe at 68F,fl owbecomesturbul entatvel oci ti esoverapproxi -matel y 6 i nches per second or about 3 i nches persecond i n a 6-i nch pi pe. These vel oci ti es are farbel owthosecommonl yencounteredi nfl ui dpowersystems, where vel oci ti es of 5 feet per second andabovearecommon.I nstreaml i nedfl ow,l ossesdue to fri cti on i ncrease di rectl y wi th vel oci ty. Wi thturbul entfl owthesel ossesi ncreasemuchmorer api dl y.FACTORSINVOLVEDINFLOWAn understandi ng of the behavi or of fl ui ds i nmoti on,orsol i dsforthatmatter,requi resanunderstandi ng of the terminertia. I nerti a i s theterm used by sci enti sts to descri be the propertypossessed by al lforms of matter that makes thematterresi stbei ngmovedi fi ti satrest,andl i kewi se, resi st any change i n i ts rate of moti oni fi ti smovi ng.Thebasi cstatementcover i ngi ner ti ai sNewtonsfi rstl awofmoti oni nerti a.Si rI saacNewtonwasaBri ti shphi l osopherandmathe-mati ci an. Hi s fi rst l aw states: A body at rest tendsto remain at rest, and a body in motion tends toremaininmotionatthesamespeedanddirection,unlessactedonbysomeunbalancedforce.Thi ssi mpl ysayswhatyouhavel ear nedbyexperi encethatyoumustpushanobjecttostarti tmovi ngandpushi ti ntheopposi tedi recti ontostopi tagai n.A fami l i ar i l l ustrati on i s the effort a pi tchermust exert to make a fast pi tch and the opposi ti onthecatchermustputforthtostopthebal l .Si mi l arl y, consi derabl e work must be performedbytheengi netomakeanautomobi l ebegi nto rol l ; al though, after i t has attai ned a certai nvel oci ty,i twi l l rol l al ongtheroadatuni formspeedi fjustenougheffor ti sexpendedtoovercome fri cti on, whi l e brakes are necessary tostop i ts moti on. I nerti a al so expl ai ns the ki ck orrecoi lof guns and the tremendous stri ki ng forceofprojecti l es.InertiaToand Forceovercomethetendencyofanobjecttoresi st any change i n i ts state of rest or moti on,someforcethati snototherwi secancel edorunbal ancedmustactontheobj ect.Someunbal ancedforcemustbeappl i edwheneverfl ui dsare set i n moti on or i ncreased i n vel oci ty; whi l econversel y, forces are made to do work el sewherewhenever fl ui dsi nmoti onar er etar dedorstopped.Therei sadi rectrel ati onshi pbetweenthemagni tudeoftheforceexertedandthei nerti aagai nstwhi chi tacts.Thi sforcei sdependentontwofactor s:(1)themassoftheobj ect(whi chi sproporti onal toi tswei ght),and(2)ther ateatwhi chthevel oci tyoftheobjecti schanged. Therul ei sthattheforcei npoundsrequi redtoovercomei nerti ai sequaltothewei ghtoftheobjectmul ti pl i edbythechange i n vel oci ty, measured i n feet per second,anddi vi dedby32ti mestheti mei nsecondsrequi redtoaccompl i shthechange.Thus,therateof change i n vel oci ty of an object i s proporti onaltotheforceappl i ed.Thenumber32appearsbecausei ti stheconversi onfactorbetweenwei ghtand mass.There are fi ve physi calfactors that can act ona fl ui d to affect i ts behavi or. Al lof the physi calacti ons of fl ui ds i n al lsystems are determi ned bytherel ati onshi psofthesefi vefactorstoeachother.Summari zi ng,thesefi vefactorsareasfol l ows:1.Gravi ty,whi chactsatal l ti mesonal lbodi es,regardl essofotherforces2.Atmospher i cpr essur e,whi chactsonanypar tofasystemexposedtotheopenai r3.Speci fi cappl i edforces,whi chmayormaynotbepresent,butwhi ch,i nanyevent,areenti rel y i ndependent of the presence or absenceofmoti on4.I nerti a,whi chcomesi ntopl aywhenevertherei sachangefromresttomoti onortheopposi te,or whenever ther ei sachangei ndi recti onori nrateofmoti on5. Fri cti on, whi ch i s al ways present whenevertherei smoti on2-11Fi gure 2-16 i l l ustrates a possi bl e rel ati onshi pof these factors wi th respect to a parti cl e of fl ui d(P)i nasystem.Thedi fferentforcesareshowni n terms of head, or i n other words, i n terms ofverti cal col umnsoffl ui drequi redtoprovi dethefor ces.Atthepar ti cul ar momentunderconsi derati on, a parti cl e of water (P) i s bei ng actedon by appl i ed force (A), by atmospheri c pressure(B),andbygravi ty(C)producedbythewei ghtof the fl ui d standi ng over i t. The parti cl e possessessuffi ci ent i nerti a or vel oci ty head to ri se to l evelP1, si nce head equi val ent to F was l ost i n fri cti onas P passed through the system. Si nce atmospheri cpressure (B) acts downward on both si des of thesystem, what i s gai ned on one si de i s l ost on theother.I fal l thepressureacti ngonPtoforcei tthrough the nozzl e coul d be recovered i n the formofel evati onhead,i twoul dri setol evel Y.I faccounti stakenofthebal ancei natmospheri cpressure, i n a fri cti onl ess system, P woul d ri se tol evel X,orpreci sel yashi ghasthesumofthegravi tyheadandtheheadequi val enttotheappl i edforce.KineticEnergyI t was previ ousl y poi nted out that a force mustbe appl i ed to an object i n order to gi ve i t a vel oci tyortoi ncreasethevel oci tyi tal readyhas.Whetherthe force begi ns or changes vel oci ty, i t acts overa certai n di stance. A force acti ng over a certai ndi stance i s work. Work and al lforms i nto whi chi tcanbechangedar ecl assi fi edasener gy.Obvi ousl ythen,energyi srequi redtogi veanobject vel oci ty. The greater the energy used, thegreater the vel oci ty wi l lbe.Di sr egar di ngfr i cti on,for anobjecttobebroughttorestorfori tsmoti ontobesl oweddown,aforceopposedtoi tsmoti onmustbeappl i edtoi t.Thi sforceal soactsoversomedi stance. I n thi s way energy i s gi ven up by theobjectanddel i veredi nsomeformtowhateveropposes i ts conti nuous moti on. The movi ng objecti sthereforeameansofrecei vi ngenergyatonepl ace (where i ts moti on i s i ncreased) and del i veri ngi ttoanother poi nt(wher ei ti sstoppedorretarded).Whi l ei ti si nmoti on,i ti ssai dtocontai n thi s energy as energy of moti on or kineticener gy.Si nce energy can never be destroyed, i t fol l owsthati ffri cti oni sdi sregardedtheenergydel i veredtostoptheobjectwi l l exactl yequal theenergythat was requi red to i ncrease i ts speed. At al lti mestheamountofki neti cenergypossessedbyanobject depends on i ts wei ght and the vel oci ty atwhi chi ti smovi ng.Figure 2-16.Physical factors governing fluid flow.2-12Themathemati cal rel ati onshi pforki neti cenergyi sstatedi ntherul e:Ki neti cenergyi nfoot-pounds i s equalto the force i n pounds whi chcreatedi t,mul ti pl i edbythedi stancethroughwhi chi twasappl i ed,ortothewei ghtofthemovi ngobjecti npounds,mul ti pl i edbythesquareof i ts vel oci ty i n feet per second, and di vi ded by64.sTher el ati onshi pbetweeni ner ti afor ces,vel oci ty, and ki neti c energy can be i l l ustrated byanal yzi ngwhathappenswhenagunfi resaprojecti l e agai nst the armor of an enemy shi p. (Seefi g.2-17.)Theexpl osi veforceofthepowderi nthe breach pushes the projecti l e out of the gun,gi vi ngi tahi ghvel oci ty.Becauseofi tsi nerti a,theprojecti l eoffersopposi ti ontothi ssuddenvel oci ty and a reacti on i s set up that pushes thegunbackward(ki ckorrecoi l ).Theforceoftheexpl osi onactsontheprojecti l ethroughouti tsmovement i n the gun. Thi s i s force acti ng througha di stance produci ng work. Thi s work appears aski neti cenergyi nthespeedi ngprojecti l e.Theresi stance of the ai r produces fri cti on, whi ch usessome of the energy and sl ows down the projecti l e.Eventual l y, however, the projecti l e hi ts i ts targetand,becauseofthei nerti a,tri estoconti nuemovi ng.Thetarget,bei ngrel ati vel ystati onary,tends to remai n stati onary because of i ts i nerti a.The resul t i s that a tremendous force i s set up thatei therl eadstothepenetrati onofthearmorortheshatteri ngoftheprojecti l e.Theprojecti l ei ssi mpl yameansoftransferri ngenergy,i nthi si nstancefordestructi vepurpose,fromthegun to the enemy shi p. Thi s energy i s transmi ttedi nthefor mofener gyofmoti onor ki neti cener gy.A si mi l ar acti on takes pl ace i n a fl ui d powersystem i n whi ch the fl ui d takes the pl ace of theprojecti l e. For exampl e, the pump i n a hydraul i cFigure 2-17.Relationship of inertia, velocity, and kineticenergy.systemi mpar tsener gytothefl ui d,whi chovercomesthei nerti aofthefl ui datrestandcauses i t to fl ow through the l i nes. The fl ui d fl owsagai nst some type of actuator that i s at rest. Thefl ui dtendstoconti nuefl owi ng,overcomesthei nerti aoftheactuator,andmovestheactuatortodowork.Fri cti onusesupaporti onoftheenergyasthefl ui dfl owsthroughthel i nesandcomponents.RELATIONSHIPOFFORCE,PRESSURE,ANDHEADI ndeal i ngwi thfl ui ds,forcesareusual l yconsi dered i n rel ati on to the areas over whi ch theyareappl i ed.Asprevi ousl ydi scussed,aforceacti ng over a uni t area i s a pressure, and pressurecan al ternatel y be stated i n pounds per square i nchor i n terms of head, whi ch i s the verti calhei ghtofthecol umnoffl ui dwhosewei ghtwoul dproducethatpressure.I n most of the appl i cati ons of fl ui d power i nthe Navy, appl i ed forces greatl y outwei gh al lotherforces, and the fl ui d i s enti rel y confi ned. Underthese ci rcumstances i t i s customary to thi nk of theforcesi nvol vedi ntermsofpressures.Si ncetheterm head i s encountered frequentl y i n the studyof fl ui d power, i t i s necessary to understand whati tmeansandhowi ti srel atedtopressureandfor ce.Al lfi ve of the factors that controlthe acti onsoffl ui dscan,ofcourse,beexpressedei therasforce,ori ntermsofequi val entpressuresorhead.I n each si tuati on, the di fferent factors are referredto i n the same terms, si nce they can be added andsubtractedtostudythei rrel ati onshi ptoeachother.At thi s poi nt you need to revi ew some termsi n generaluse. Gravi ty head, when i t i s i mportantenoughtobeconsi dered,i ssometi mesreferredto as head. The effect of atmospheri c pressure i sreferredtoasatmospheri cpressure.(Atmospheri cpressure i s frequentl y and i mproperl y referred toassucti on.)I nerti aeffect,becausei ti sal waysdi rectl yrel atedtovel oci ty,i susual l ycal l edvel oci ty head; and fri cti on, because i t representsa l oss of pressure or head, i s usual l y referred toasfri cti onhead.STATICANDDYNAMICFACTORSGr avi ty,appl i edfor ces,andatmospher i cpressure are stati c factors that appl y equal l y to2-13fl ui dsatrestori nmoti on,whi l ei nerti aandfri cti onaredynami cfactorsthatappl yonl ytofl ui dsi nmoti on.Themathemati cal sumofgravi ty, appl i ed force, and atmospheri c pressurei s the stati c pressure obtai ned at any one poi nti n a fl ui d at any gi ven ti me. Stati c pressure exi stsi n addi ti on to any dynami c factors that may al sobe present at the same ti me.Remember,Pascal sl awstatesthatapressureset up i n a fl ui d acts equal l y i n al ldi recti ons andatri ghtangl estothecontai ni ngsurfaces.Thi scoversthesi tuati ononl yforfl ui dsatrestorpracti cal l y at rest. I t i s true onl y for the factorsmaki ng up stati c head. Obvi ousl y, when vel oci tybecomesafactori tmusthaveadi recti on,andas previ ousl y expl ai ned, the force rel ated to thevel oci tymustal sohaveadi r ecti on,sothatPascal s l aw al one does not appl y to the dynami cfactorsoffl ui dpower.The dynami c factors of i nerti a and fri cti on arerel atedtothestati cfactors.Vel oci tyheadandfri cti on head are obtai ned at the expense of stati chead. However, a porti on of the vel oci ty head canal waysbereconvertedtostati chead.Force,whi chcan be produced by pressure or head when deal i ngwi th fl ui ds, i s necessary to start a body movi ngi f i t i s at rest, and i s present i n some form whenthemoti onofthebodyi sarrested;therefore,wheneverafl ui di sgi venvel oci ty,somepartofi tsori gi nal stati cheadi susedtoi mpartthi svel oci ty,whi chthenexi stsasvel oci tyhead.BERNOULLISPRINCIPLEConsi derthesystemi l l ustratedi nfi gure2-18.Chamber A i s under pressure and i s connected bya tube to chamber B, whi ch i s al so under pressure.The pressure i n chamber A i s stati c pressure of100 psi . The pressure at some poi nt (X) al ong theconnecti ng tube consi sts of a vel oci ty pressure ofFigure 2-18.Relation of static and dynamic factorsBernoullisprinciple.10 psiexerted i n a di recti on paral l elto the l i neof fl ow, pl us the unused stati c pressure of 90 psi ,whi ch sti l lobeys Pascal s l aw and operates equal l yi nal l di recti ons.Asthefl ui denterschamberBi t i s sl owed down, and i ts vel oci ty i s changed backtopressure.Theforcerequi redtoabsorbi tsi nerti a equal s the force requi red to start the fl ui dmovi ng ori gi nal l y, so that the stati c pressure i nchamberBi sequal tothati nchamberA.Thi ssi tuati on(fi g.2-18)di sregardsfri cti on;therefore, i t woul d not be encountered i n actualpr acti ce.For ceor headi sal sor equi r edtoovercomefri cti onbut,unl i kei nerti aeffect,thi sforcecannotberecoveredagai n,al thoughtheenergyrepresentedsti l l exi stssomewhereasheat.Therefore,i nanactual systemthepressurei nchamber B woul d be l ess than i n chamber A bytheamountofpr essur eusedi nover comi ngfri cti onal ongtheway.At al lpoi nts i n a system the stati c pressure i sal waystheori gi nal stati cpressure,l essanyvel oci tyhead at the poi nt i n questi on and l ess the fri cti onhead consumed i n reachi ng that poi nt. Si nce boththe vel oci ty head and the fri cti on head representenergy that came from the ori gi nalstati c head,and si nce energy cannot be destroyed, the sum ofthe stati c head, the vel oci ty head, and the fri cti onhead at any poi nt i n the system must add up totheor i gi nal stati chead.Thi si sknownasBer noul l i 'spr i nci pl e,whi chstates:Forthehorizontalflowoffluidthroughatube,thesumofthepressureandthekineticenergyperunitvolumeofthefluidisconstant.Thi spr i nci pl egovernstherel ati onsofthestati canddynami cfactorsconcerni ngfl ui ds,whi l ePascal sl awstatesthemanneri nwhi chthestati cfactorsbehavewhen taken by themsel ves.MINIMIZINGFRICTIONFl ui d power equi pment i s desi gned to reducefri cti on to the l owest possi bl e l evel . Vol ume andvel oci tyoffl owaremadethesubjectofcarefulstudy. The proper fl ui d for the system i s chosen.Cl ean, smooth pi pe of the best di mensi ons for theparti cul ar condi ti ons i s used, and i t i s i nstal l edal ong as di rect a route as possi bl e. Sharp bendsand sudden changes i n cross-secti onalareas areavoi ded.Val ves,gauges,andothercomponentsare desi gned to i nterrupt fl ow as l i ttl e as possi bl e.Carefulthought i s gi ven to the si ze and shape ofthe openi ngs. The systems are desi gned so they2-14canbekeptcl eani nsi deandvari ati onsfromnormal operati oncaneasi l ybedetectedandr emedi ed.OPERATIONOFHYDRAULICCOMPONENTSTotr ansmi tandcontr ol power thr oughpr essur i zedfl ui ds,anar r angementofi nter -connectedcomponentsi sr equi r ed.Suchanarrangement i s commonl y referred to as a system.The number and arrangement of the componentsvaryfromsystemtosystem,dependi ngontheparti cul ar appl i cati on. I n many appl i cati ons, onemai n system suppl i es power to severalsubsystems,whi ch are someti mes referred to as ci rcui ts. Thecompl etesystemmaybeasmal l compactuni t;more often, however, the components are l ocatedat wi del y separated poi nts for conveni ent controlandoperati onofthesystem.The basi c components of a fl ui d power systemare essenti al l y the same, regardl ess of whether thesystem uses a hydraul i c or a pneumati c medi um.There are fi ve basi c components used i n a system.Thesebasi ccomponentsareasfol l ows:1.2.3.4.5.Reservoi rorrecei verPumporcompressorLi nes(pi pe,tubi ng,orfl exi bl ehose)Di recti onal control val veActuati ngdevi ceSeveral appl i cati onsoffl ui dpowerrequi reonl y a si mpl e system; that i s, a system whi ch usesonl yafewcomponentsi naddi ti ontothefi vebasi c components. A few of these appl i cati ons arepresentedi nthefol l owi ngparagraphs.Wewi l lexpl ai n the operati on of these systems bri efl y atthi sti mesoyouwi l l knowthepurposeofeachcomponentandcanbetter under standhowhydraul i csi susedi ntheoperati onofthesesystems. More compl ex fl ui d power systems aredescri bed i n chapter 12.HYDRAULICJ ACKThehydraul i cjacki sperhapsoneofthesi mpl estfor msofafl ui dpower system.Bymovi ng the handl e of a smal ldevi ce, an i ndi vi dualcanl i ftal oadwei ghi ngseveral tons.Asmal li ni ti alforce exerted on the handl e i s transmi ttedby a fl ui d to a much l arger area. To understandthi sbetter,studyfi gure2-19.Thesmal l i nputpi stonhasanareaof5squarei nchesandi sdi rectl yconnectedtoal argecyl i nderwi thanoutput pi ston havi ng an area of 250 square i nches.Thetopofthi spi stonformsal i ftpl atform.I f a force of 25 pounds i s appl i ed to the i nputpi ston, i t produces a pressure of 5 psii n the fl ui d,thati s,ofcour se,i fasuffi ci entamountofresi stantforcei sacti ngagai nstthetopoftheoutputpi ston.Di sregardi ngfri cti onl oss,thi spressure acti ng on the 250 square i nch area of theoutputpi stonwi l l supportaresi stanceforceof1,250 pounds. I n other words, thi s pressure coul dovercome a force of sl i ghtl y under 1,250 pounds.An i nput force of 25 pounds has been transformedi ntoaworki ngforceofmorethanhal faton;however, for thi s to be true, the di stance travel edby the i nput pi ston must be 50 ti mes greater thanthe di stance travel ed by the output pi ston. Thus,foreveryi nchthatthei nputpi stonmoves,theoutputpi stonwi l l moveonl yone-fi fti ethofani n c h .Thi s woul d be i deali f the output pi ston neededto move onl y a short di stance. However, i n mosti nstances,theoutputpi stonwoul dhavetobecapabl e of movi ng a greater di stance to serve apracti calappl i cati on. The devi ce shown i n fi gure2-19 i s not capabl e of movi ng the output pi stonfartherthanthatshown;therefore,someothermeans must be used to rai se the output pi ston toa greater hei ght.Figure2-19.Hydraulicjack.2-15Theoutputpi stoncanberai sedhi gherandmai ntai ned at thi s hei ght i f addi ti onalcomponentsarei nstal l edasshowni nfi gure2-20.I nthi si l l ustrati on the jack i s desi gned so that i t can berai sed,l owered,orhel dataconstanthei ght.These resul ts are attai ned by i ntroduci ng a numberof val ves and al so a reserve suppl y of fl ui d to beused i n the system.Noti ce that thi s system contai ns the fi ve basi ccomponentsthereservoi r;cyl i nder1,whi chservesasapump;val ve3,whi chservesasadi recti onalcontrolval ve; cyl i nder 2, whi ch servesas the actuati ng devi ce; and l i nes to transmi t thefl ui dtoandfromthedi fferentcomponents.I naddi ti on, thi s system contai ns two val ves, 1 and2, whose functi ons are expl ai ned i n the fol l owi ngdi scussi on.As the i nput pi ston i s rai sed (fi g. 2-20, vi ewA),val ve1i scl osedbythebackpressurefromthe wei ght of the output pi ston. At the same ti me,val ve 2 i s opened by the head of the fl ui d i n thereservoi r. Thi s forces fl ui d i nto cyl i nder 1. Whenthe i nput pi ston i s l owered (fi g. 2-20, vi ew B), apressurei sdevel opedi ncyl i nder1.Whenthi spressure exceeds the head i n the reservoi r, i t cl osesval ve 2. When i t exceeds the back pressure fromthe output pi ston, i t opens val ve 1, forci ng fl ui di nto the pi pel i ne. The pressure from cyl i nder 1 i sFigure 2-20.Hydraulic jack; (A) up stroke; (B) downstroke.thus transmi tted i nto cyl i nder 2, where i t acts torai setheoutputpi stonwi thi tsattachedl i ftpl atform. When the i nput pi ston i s agai n rai sed,thepressurei ncyl i nder1dropsbel owthati ncyl i nder 2, causi ng val ve 1 to cl ose. Thi s preventsthereturnoffl ui dandhol dstheoutputpi stonwi thi tsattachedl i ftpl atformati tsnewl evel .Duri ng thi s stroke, val ve 2 opens agai n al l owi nga new suppl y of fl ui d i nto cyl i nder 1 for the nextpower(downward)strokeofthei nputpi ston.Thus, by repeated strokes of the i nput pi ston, thel i ft pl atform can be progressi vel y rai sed. To l owerthe l i ft pl atform, val ve 3 i s opened, and the fl ui dfromcyl i nder2i sreturnedtothereservoi r.HYDRAULICBRAKESThehydr aul i cbr akesystemusedi ntheautomobi l e i s a mul ti pl e pi ston system. A mul ti pl epi ston system al l ows forces to be transmi tted totwo or more pi stons i n the manner i ndi cated i nfi gure 2-21. Note that the pressure set up by theforce appl i ed to the i nput pi ston (1) i s transmi ttedundi mi ni shedtobothoutputpi stons(2and3),andthattheresul tantforceoneachpi stoni sproporti onal toi tsarea.Themul ti pl i cati onofforces from the i nput pi ston to each output pi stoni s the same as that expl ai ned earl i er.The hydraul i c brake system from the mastercyl i nder stothewheel cyl i nder sonmostFigure 2-21.Multiple piston system.2-16automobi l esoperatesi nawaysi mi l artothesystem i l l ustrated i n fi gure 2-22.Whenthebr akepedal i sdepr essed,thepressureonthebrakepedal movesthepi stonwi thi nthemastercyl i nder,forci ngthebrakefl ui dfrom the master cyl i nder through the tubi ng andfl exi bl ehosetothewheel cyl i nders.Thewheelcyl i nderscontai ntwoopposedoutputpi stons,each of whi ch i s attached to a brake shoe fi ttedi nsi dethebrakedrum.Eachoutputpi stonpushesthe attached brake shoe agai nst the wal lof thebrakedrum,thusretardi ngtherotati onofthewheel . When pressure on the pedali s rel eased, thespri ngsonthebrakeshoesreturnthewheelcyl i nder pi stons to thei r rel eased posi ti ons. Thi sacti onfor cesthedi spl acedbr akefl ui dbackthrough the fl exi bl e hose and tubi ng to the mastercyl i nder.The force appl i ed to the brake pedalproducesapr opor ti onal for ceoneachoftheoutputpi stons,whi chi nturnappl ythebrakeshoesfr i cti onal l ytothetur ni ngwheel stor etar drotati on.As previ ousl y menti oned, the hydraul i c brakesystem on most automobi l es operates i n a si mi l arway,asshowni nfi gure2-22.I ti sbeyondthescope of thi s manualto di scuss the vari ous brakesystems.Figure2-22.Anautomobilebrakesystem.2-17CHAPTER 3HYDRAULIC FLUIDSDuri ng the desi gn of equi pment that requi resfl ui dpower ,manyfactor sar econsi der edi nsel ecti ng the type of system to be usedhydraul i c,pneumati c,oracombi nati onofthetwo.Someof the factors are requi red speed and accuracy ofoperati on,surroundi ngatmospheri ccondi ti ons,economi ccondi ti ons,avai l abi l i tyofrepl acementfl ui d, requi red pressure l evel , operati ng tempera-turerange,contami nati onpossi bi l i ti es,costoftransmi ssi on l i nes, l i mi tati ons of the equi pment,l ubri ci ty,safetytotheoperators,andexpectedservi cel i feoftheequi pment.Afterthetypeofsystemhasbeensel ected,manyofthesesamefactorsmustbeconsi deredi n sel ecti ng the fl ui d for the system. Thi s chapteri s devoted to hydraul i c fl ui ds. I ncl uded i n i t aresecti onsontheproperti esandcharacteri sti csdesi redofhydraul i cfl ui ds;typesofhydraul i cfl ui ds;hazardsandsafetyprecauti onsforworki ngwi th,handl i ng, anddi sposi ngofhydr aul i cl i qui ds; types and controlof contami nati on; andsampl i ng.PROPERTIESI f fl ui di ty (the physi calproperty of a substancethatenabl esi ttofl ow)andi ncompressi bi l i tyweretheonl yproperti esrequi red,anyl i qui dnottoothi ckmi ghtbeusedi nahydr aul i csystem.However,asati sfactoryl i qui dforaparti cul arsystem must possess a number of other properti es.The most i mportant properti es and some charac-teri sti cs are di scussed i n the fol l owi ng paragraphs.VISCOSITYVi scosi tyi soneofthemosti mpor tantproperti es of hydraul i c fl ui ds. I t i s a measure ofafl ui dsresi stancetofl ow.Al i qui d,suchasgasol i ne, whi ch fl ows easi l y has a l ow vi scosi ty;and a l i qui d, such as tar, whi ch fl ows sl owl y hasahi ghvi scosi ty.Thevi scosi tyofal i qui di saffectedbychangesi ntemperatureandpressure.Asthetemperatureofal i qui di ncreases,i tsvi scosi ty decreases. That i s, a l i qui d fl ows moreeasi l ywheni ti shotthanwheni ti scol d.Thevi scosi ty of a l i qui d i ncreases as the pressure onthe l i qui d i ncreases.Asati sfactoryl i qui dforahydraul i csystemmustbethi ckenoughtogi veagoodseal atpumps,motors,val ves,andsoon.Thesecom-ponentsdependoncl osefi tsforcreati ngandmai ntai ni ngpr essur e.Anyi nter nal l eakagethrough these cl earances resul ts i n l oss of pressure,i nstantaneouscontr ol ,andpumpeffi ci ency.Leakagel ossesaregreaterwi ththi nnerl i qui ds(l ow vi scosi ty). A l i qui d that i s too thi n wi l lal soal l ow rapi d weari ng of movi ng parts, or of partsthatoperateunderheavyl oads.Ontheotherhand, i f the l i qui d i s too thi ck (vi scosi ty too hi gh),thei nternal fri cti onofthel i qui dwi l l causeani ncreasei nthel i qui dsfl owresi stancethroughcl ear ancesofcl osel yfi ttedpar ts,l i nes,andi nternalpassages. Thi s resul ts i n pressure dropsthr oughoutthesystem,sl uggi shoper ati onoftheequi pment,andani ncreasei npowerconsumpti on.Measurement of ViscosityVi scosi ty i s normal l y determi ned by measuri ngtheti merequi redforafi xedvol umeofafl ui d(atagi ventemper atur e)tofl owthr oughacal i bratedori fi ceorcapi l l arytube.Thei nstru-ments used to measure the vi scosi ty of a l i qui dareknownasvi scometersorvi scosi meters.Severaltypes of vi scosi meters are i n use today.TheSaybol tvi scometer,showni nfi gure3-1,measurestheti merequi red,i nseconds,for60mi l l i l i tersofthetestedfl ui dat100Ftopassthrough a standard ori fi ce. The ti me measured i s3-1Figure 3-1.Saybolt viscometer.usedtoexpressthefl ui dsvi scosi ty,i nSaybol tuni versal secondsorSaybol tfurol seconds.Thegl asscapi l l aryvi scometers,showni nfi gure3-2,areexampl esofthesecondtypeofvi scometerused.Thesevi scometersareusedtomeasureki nemati cvi scosi ty.Li ketheSaybol tvi scometer, the gl ass capi l l ary measures the ti mei nsecondsrequi redforthetestedfl ui dtofl owthrough the capi l l ary. Thi s ti me i s mul ti pl i ed bythetemperatureconstantofthevi scometeri nusetoprovi dethevi scosi ty,expressedi ncenti strokes.Thefol l owi ngfor mul asmaybeusedtoconvertcenti strokes(cStuni ts)toapproxi mateSaybol tuni versal seconds(SUSuni ts).For SUS val ues between 32 and 100:For SUS val ues greater than 100:Al thoughthevi scometersdi scussedaboveareused i n l aboratori es, there are other vi scometersi n the suppl y system that are avai l abl e for l ocaluse.Thesevi scometerscanbeusedtotestthevi scosi ty of hydraul i c fl ui ds ei ther pri or to thei rbei ngaddedtoasystemorperi odi cal l yaftertheyhave been i n an operati ng system for a whi l e.Figure 3-2.Various styles of glass capillary viscometers.3-2Addi ti onal i nformati ononthevari oustypesof vi scometers and thei r operati on can be foundi n the PhysicalMeasurementsTrainingManual,NAVAI R17-35QAL-2.Viscosity IndexThe vi scosi ty i ndex (V.I .) of an oi li s a numberthat i ndi cates the effect of temperature changesonthevi scosi tyoftheoi l .Al owV.I .si gni fi esarel ati vel yl argechangeofvi scosi tywi thchangesof temperature. I n other words, the oi lbecomesextremel y thi n at hi gh temperatures and extremel ythi ck at l ow temperatures. On the other hand, ahi ghV.I .si gni fi esr el ati vel yl i ttl echangei nvi scosi tyoverawi detemperaturerange.Ani deal oi l for mostpur posesi sonethatmai ntai nsaconstantvi scosi tythroughouttemperature changes. The i mportance of the V.I .canbeshowneasi l ybyconsi deri ngautomoti vel ubr i cants.Anoi l havi ngahi ghV.I .r esi stsexcessi ve thi ckeni ng when the engi ne i s col d and,consequentl y,promotesrapi dstarti ngandpromptci rcul ati on; i t resi sts excessi ve thi nni ng when themotor i s hot and thus provi des ful ll ubri cati on andpreventsexcessi veoi l consumpti on.Another exampl e of the i mportance of the V.I .i s the need for a hi gh V.I . hydraul i c oi lfor mi l i taryai rcraft, si nce hydraul i c controlsystems may beexposedtotemperaturesrangi ngfrombel ow65Fathi ghal ti tudestoover100Fontheground. For the proper operati on of the hydraul i ccontrol system,thehydraul i cfl ui dmusthaveasuffi ci entl y hi gh V.I . to perform i ts functi ons atthe extremes of the expected temperature range.Li qui ds wi th a hi gh vi scosi ty have a greaterresi stancetoheatthanl owvi scosi tyl i qui dswhi chhavebeenderi vedfromthesamesource.Theaveragehydraul i cl i qui dhasarel ati vel yl owvi scosi ty.Fortunatel y,therei sawi dechoi ceofl i qui dsavai l abl eforusei nthevi scosi tyrangerequi redofhydraul i cl i qui ds.TheV.I .ofanoi l maybedetermi nedi fi tsvi scosi tyatanytwotemperaturesi sknown.Tabl es,basedonal argenumberoftests,arei ssuedbytheAmer i canSoci etyfor Testi ngandMater i al s(ASTM).Thesetabl esper mi tcal cul ati onoftheV.I .fromknownvi scosi ti es.LUBRICATINGPOWERI fmoti ontakespl acebetweensurfacesi ncontact,fri cti ontendstoopposethemoti on.Whenpressureforcesthel i qui dofahydraul i csystem between the surfaces of movi ng parts, thel i qui d spreads out i nto a thi n fi l m whi ch enabl esthe parts to move more freel y. Di fferent l i qui ds,i ncl udi ngoi l s,varygreatl ynotonl yi nthei rl ubri cati ng abi l i ty but al so i n fi l m strength. Fi l mstrength i s the capabi l i ty of a l i qui d to resi st bei ngwi ped or squeezed out from between the surfaceswhenspreadouti nanextremel ythi nl ayer.Al i qui d wi l lno l onger l ubri cate i f the fi l m breaksdown, si nce the moti on of part agai nst part wi pesthemetal cl eanofl i qui d.Lubri cati ngpowervari eswi thtemperaturechanges;therefore,thecl i mati candworki ngcondi ti onsmustenteri ntothedetermi nati onofthel ubr i cati ngqual i ti esofal i qui d.Unl i kevi scosi ty,whi chi saphysi cal pr oper ty,thel ubri cati ngpowerandfi l mstrengthofal i qui di sdi r ectl yr el atedtoi tschemi cal natur e.Lubri cati ngqual i ti esandfi l mstrengthcanbei mprovedbytheaddi ti onofcertai nchemi calagents.CHEMICALSTABILITYChemi calstabi l i ty i s another property whi chi sexceedi ngl yi mportanti nthesel ecti onofahydraul i c l i qui d. I t i s defi ned as the l i qui ds abi l i tytoresi stoxi dati onanddeteri orati onforl ongperi ods. Al ll i qui ds tend to undergo unfavorabl echanges under severe operati ng condi ti ons. Thi si s the case, for exampl e, when a system operatesfor aconsi der abl eper i odofti meathi ghtemper atur es.Excessi ve temperatures, especi al l y extremel yhi gh temperatures, have a great effect on the l i feof a l i qui d. The temperature of the l i qui d i n thereservoi rofanoperati nghydraul i csystemdoesnotal waysi ndi catetheoperati ngcondi ti onsthroughout the system. Local i zed hot spots occuron beari ngs, gear teeth, or at other poi nts wherethe l i qui d under pressure i s forced through smal lori fi ces.Conti nuouspassageofthel i qui dthroughthesepoi ntsmayproducel ocal temperatureshi ghenoughtocarboni zethel i qui dorturni ti ntosl udge,yetthel i qui di nthereservoi rmaynoti ndi cate an excessi vel y hi gh temperature.Li qui dsmaybreakdowni fexposedtoai r,water, sal t, or other i mpuri ti es, especi al l y i f theyare i n constant moti on or subjected to heat. Somemetal s, such as zi nc, l ead, brass, and copper, haveundesi r abl echemi cal r eacti onswi thcer tai nl i qui ds.These chemi calreacti ons resul t i n the forma-ti onofsl udge,gums,carbon,orotherdeposi tswhi ch cl og openi ngs, cause val ves and pi stons tosti ck or l eak, and gi ve poor l ubri cati on to movi ng3-3parts.Onceasmal l amountofsl udgeorotherdeposi tsi sformed,therateofformati ongeneral l yi ncreasesmorerapi dl y.Asthesedeposi tsarefor med,cer tai nchangesi nthephysi cal andchemi calproperti es of the l i qui d take pl ace. Thel i qui dusual l ybecomesdar ker ,thevi scosi tyi ncreasesanddamagi ngaci dsareformed.Theextenttowhi chchangesoccuri ndi fferentl i qui dsdependsonthetypeofl i qui d,typeofrefi ni ng,andwhetheri thasbeentreatedtopr ovi defur ther r esi stancetooxi dati on.Thestabi l i tyofl i qui dscanbei mpr ovedbytheaddi ti onofoxi dati oni nhi bi tor s.I nhi bi tor ssel ected to i mprove stabi l i ty must be compati bl ewi th the other requi red properti es of the l i qui d.FREEDOMFROMACIDITYAn i dealhydraul i c l i qui d shoul d be free fromaci ds whi ch cause corrosi on of the metal s i n thesystem. Most l i qui ds cannot be expected to remai ncompl etel ynoncorrosi veundersevereoperati ngcondi ti ons. The degree of aci di ty of a l i qui d, whennew, may be sati sfactory; but after use, the l i qui dmaytendtobecomecorrosi veasi tbegi nstodeter i or ate.Many systems are i dl e for l ong peri ods afteroperati ngathi ghtemperatures.Thi spermi tsmoi sture to condense i n the system, resul ti ng i nrustformati on.Certai ncorrosi on-andrust-preventi veaddi -ti ves are added to hydraul i c l i qui ds. Some of theseaddi ti ves are effecti ve onl y for a l i mi ted peri od.Therefore, the best procedure i s to use the l i qui dspeci fi ed for the system for the ti me speci fi ed bythesystemmanufacturerandtoprotectthel i qui dandthesystemasmuchaspossi bl efr omcontami nati on by forei gn matter, from abnormaltemperatures,andfrommi suse.FLASHPOINTFl ashpoi nt i s the temperature at whi ch a l i qui dgi vesoffvapori nsuffi ci entquanti tytoi gni temomentari l y or fl ash when a fl ame i s appl i ed. Ahi gh fl ashpoi nt i s desi rabl e for hydraul i c l i qui dsbecausei tprovi desgoodresi stancetocombusti onandal owdegr eeofevapor ati onatnor maltemperatures.Requi redfl ashpoi ntmi ni mumsvary from 300F for the l i ghtest oi l s to 510F forthe heavi est oi l s.FIRE POINTFi repoi nti sthetemperatureatwhi chasubstancegi vesoffvapori nsuffi ci entquanti tyto i gni te and conti nue to burn when exposed toa spark or fl ame. Li ke fl ashpoi nt, a hi gh fi re poi nti srequi redofdesi rabl ehydraul i cl i qui ds.MINIMUMTOXICITYToxi ci tyi sdefi nedasthequal i ty,state,ordegree of bei ng toxi c or poi sonous. Some l i qui dscontai n chemi cal s that are a seri ous toxi c hazard.These toxi c or poi sonous chemi cal s may enter thebodythroughi nhal ati on,byabsorpti onthroughthe ski n, or through the eyes or the mouth. Theresul ti ssi cknessand,i nsomecases,death.Manufactur er sofhydr aul i cl i qui dsstr i vetoproducesui tabl el i qui dsthatcontai nnotoxi cchemi cal s and, as a resul t, most hydraul i c l i qui dsarefreeofharmful chemi cal s.Somefi re-resi stantl i qui ds are toxi c, and sui tabl e protecti on and carei nhandl i ngmustbeprovi ded.DENSITYANDCOMPRESSIBILITYA fl ui d wi th a speci fi c gravi ty of l ess than 1.0i s desi red when wei ght i s cri ti cal , al though wi thpropersystemdesi gn,afl ui dwi thaspeci fi cgravi ty greater than one can be tol erated. Whereavoi dance of detecti on by mi l i tary uni ts i s desi red,a fl ui d whi ch si nks rather than ri ses to the surfaceof the water i s desi rabl e. Fl ui ds havi ng a speci fi cgravi ty greater than 1.0 are desi red, as l eaki ngfl ui d wi l lsi nk, al l owi ng the vesselwi th the l eaktoremai nundetected.Recal l fromchapter2thatunderextremepressureafl ui dmaybecompressedupto7per centofi tsor i gi nal vol ume.Hi ghl ycom-pressi bl e fl ui ds produce sl uggi sh system operati on.Thi s does not present a seri ous probl em i n smal l ,l ow-speed operati ons, but i t must be consi deredi n the operati ng i nstructi ons.FOAMINGTENDENCIESFoami sanemul si onofgasbubbl esi nthefl ui d.Foami nahydraul i csystemresul tsfromcompressed gases i n the hydraul i c fl ui d. A fl ui dunder hi gh pressure can contai n a l arge vol umeof ai r bubbl es. When thi s fl ui d i s depressuri zed,as when i t reaches the reservoi r, the gas bubbl esi nthefl ui dexpandandpr oducefoam.Anyamountoffoami ngmaycausepumpcavi tati onandproducepoorsystemresponseandspongy3-4control .Therefore,defoami ngagentsareoftenaddedtofl ui dstopreventfoami ng.Mi ni mi zi ngai ri nfl ui dsystemsi sdi scussedl ateri nthi schapter.CLEANLINESSCl eanl i ness i n hydraul i c systems has recei vedconsi derabl eattenti onrecentl y.Somehydraul i csystems,suchasaerospacehydraul i csystems,areextr emel ysensi ti vetocontami nati on.Fl ui dcl eanl i nessi sofpri maryi mportancebecausecontami nants can cause component mal functi on,pr eventpr oper val veseati ng,causewear i ncomponents, and may i ncreas