1.Whenliftingheavyweights,themandrilfailstorisetothemaximumroute.Whenthejackreachesacertainheight,andthemaximumrouteisnotreached,themandrilcannotriseupanymore,whichindicatesthatthereisalackofworkingoilinthejack,anditshouldbereplenished.

2.Themandrilwobbleswhilerising.Generallytheoilreturnvalveisnotclosedtightly;wecantightenoilreturnvalveneedleincounterclockwisedirection.Ifitisstillunstable,checkwhetherthereisanyoilleakagearoundthepressurerod;iftheoilleaks,itindicatesthatthesealringofthemandrilisdamaged,anditshouldbereplaced.Ifthereisnooilleakage,confirmagainwhethertheoilreturnvalveandtheinletvalveisalreadylocked,andalsochecksealinggasketconditionsinthecylinderendjointofpressurerod;ifalltheaboveisnormal,thenitindicatesthatthesealringisdamaged,orthefixedscrewisloosening,weshouldreplaceitortightenthescrew.

3.Themandrilfailstorisewhileno-load.Firstchecktheoilamountofthejack,andweshouldaddoilwheninsufficient.Ifjackisnotshortofoil,wecanloosentheoilreturnvalveneedleofthejack,removetheoilplugofoilfillingport,thentrampleonthejackbasebyourfeet,repeatedlypullupthemandrilandpressdownagainbyourhandsforseveraltimes,inordertoexhaustair;aftertheaboveactionsarecompleted,tightentheoilplugofoilfillingportandoilreturnvalvetightly,andthentryagaintheno-loadmandril;ifthemandrilstillcannotrise,layjackflat,removetheoilreturnvalve,checkwhetherthevalveandseatcontactwell;ifthereisdirt,itshouldberemoved;ifthereispit,slotanduneven,itshouldbereplaced.Finallycheckwhethertheoilinletvalveiswellsealedandthesealingringofmandrilisdamagedorfallsoff.Ifany,replaceitintime.

4.Oilleakage,canbeseenbyvisualobservation.Theoilleakageareaofthejackisusuallyinthebaseandthecylinderjoint,aroundthemandril,inthelockthreadoftheoilreturnvalve,inthefixedoilplugoftheoilfillingport,aroundpressurerodetc.Thecauseofoilleakageisusuallythedamageofsealinggasket,itmustbereplacedintime.