Hidraulika Eng Prezentacija

8/9/2019 Hidraulika Eng Prezentacija

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HYDRAULICS


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WHAT ISHYDRAULICS?

Hydraulics is a topic in applied science

and engineering dealing with themechanical properties of liquids.Hydraulics topics range through somepart of science and most of

engineering modules, and coverconcepts such as pipe ow, damdesign, uidics and uid controlciruitry, pumps, turbines, hydropower,

computational uid dynamics, owmeasurement, river channel behaviorand erosion.


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WHY?

It is ismportant that a hydraulicsystem contains no air

bubbles.

If there is an air bubble in thesystem, then the force applied tothe rst piston gets used

compressing the air in the bubblerather than moving the secondpiston, which has a big eect on

the eciency of the system.


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5/17

Two pistons t into two !"#ss $%"in&'(s ""'& wit) oi" #n&$onn'$t'& to on' #not)'( wit) #n oi"*""'& pip'. I+ %o, #pp"%# &ownw#(& +o($' to on' piston -t)' "'+t on' in t)is &(#win!/t)'n t)' +o($' is t(#ns0itt'& to t)' s'$on& piston t)(o,!)t)' oi" in t)' pip'.

"ince oil is incompressible, the eciency is very good## almost all of the applied force appears at the secondpiston.

he great thing about hydraulic systems is that the pipeconnecting the two cylinders can be any length and shape,allowing it to sna$e through all sorts of things separating thetwo pistons. he pipe can also for$, so that one mastercylinder can drive more than one slave cylinder if desired.


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WHAT ARE

HYDRAULIC PUMPS?

Hydraulic pumps are sources of powerfor many dynamic machines.

Hydraulic pumps are capable ofpushing large amounts of oil throughhydraulic cylinders or hydraulic

motors. In this fashion, thepump converts the mechanicalenergy of the drive &i.e. torque,speed' into hydrostatic energy &i.e.ow, pressure'.

Hydraulic pumps operate according to thedisplacement principle. his involves the

e(istence of mechanically sealed chambersin the pump. hrough these chambers,uid is transported from the inlet &suctionport' of the pump to the outlet &pressure

port'. he sealed chambers ensure thatthere is no direct connection between thetwo ports of the pump. )s a result, these

pumps are very suitable to operate at highsystem pressures and are ideal forhydraulics.


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Hydraulic pumps are manufactured

depending on dierent functional andhydraulic system requirements, such asoperating medium, required range ofpressure, type of drive, etc. ) large range ofdesign principles and congurations e(istsbehind hydraulic pumps. *onsequently, notevery pump can fully meet all sets of

requirements to an optimum degree.

hree dierent types ofhydraulic pumps e(ist!

+. Hydraulic gear pumps

. Hydraulic vane pumps

-. Hydraulic piston pumps


8/17

Hydraulic gear pump is used in many

hydraulic systems. It has few movingparts, wor$s smoothly, and operatesvery well at pressures up to / bar.

he displacement chambers areformed between the housing of thepump and the rotating gear wheel &orgear wheels, depending on model'.

here are four dierent types ofhydraulic gear pumps!

+.0(ternal gear pumps.Internal gear pumps-.1ear ring pumps

2."crew spindle

used in industrial and mobile &e.g. log splitters, lifts' hydraulic applications. ypicalapplications are lubrication pumps in machine tools, uid power transfer units and oilpumps in engines. hese pumps have some unique features!

3ow weight 4elatively high wor$ing pressures

5ide range of speeds 5ide temperature and viscosity range &i.e. e(ibility' 3ow cost

In an e(ternal gear pump, only one of the gear wheels is connected to the drive. heother gear wheel rotates in the opposite direction so that the teeth of the rotating gearwheels interloc$. 5ith use of a bearing bloc$, the gear wheels are positioned in such away that they interloc$ with the minimum clearance. 6olume is created between thegear tooth proles, housing walls and surfaces of the bearing bloc$s.

ypical parameters are! 7isplacement volume! /. to // cc 8a(imum pressure! up to -// bar &si9e dependent' "peed range! // to :,/// rpm

primarily used in non#mobile hydraulics &e.g. machines for plastics and machinetools, presses, etc.' and in vehicles that operate in an enclosed space &electric for$#

lifts, etc.'. he internal gear pump is e(ceptionally versatile and also capable ofhandling thic$ uids. ;ey features are! 3ow ow pulsation 3ow operating noise High eciency

In an internal gear pump, the gear rotor is connected to the drive. 5hen the gearrotor and internal gear rotate, volume is created between the gear ring proles,housing walls and lling piece. he space between the gear tooth proles increases

relatively slowly over an angle of about +/


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he vane pump nds its use in die casting andin>ection moulding machines in industry, as well

as in land and road construction machinery.

Hydraulic vane pumps operate with much lowerow pulsation, i.e. constant ow. )s such, vane

pumps produce less noise while maintaining arelatively high speed.

;ey features of the vane pump!

3ow ow pulsation 6ery low noise levels

5ide range of speeds

5ide viscosity range

he operating pressure of vane pumps does notnormally e(ceed +? bar. However, in speciallydesigned vane pumps the operating pressuremay go over // bar and up to -// bar. Hydraulic

vane pumps are available as single chamber vanepumps or double chamber vane pumps.

ypical parameters are!7isplacement volume! : to :2/ cc8a(imum pressure! up to // bar

"peed range! // to -,/// rpm


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Do,1"' C)#01'( 2#n' P,0p@or double chamber vane pumps, the process of lling the chambers&suction' and emptying is in principle the same as for single chamber

vane pumps. In this case, however, the stro$e ring &i.e. stator' has adouble eccentric internal surface. he rotor can be placed in the a(isof the stator because of these surfaces, which dierentiates themfrom single chamber vane pumps.

his set up causes each vane to carry out two stro$es per rotation of

the shaft. )ll radial loads on the rotor are now neutrali9ed &twopressure ports on each opposite side'. he end result is that twopumps have been built together as one. 7ue to the twin cam forms ofthe stator, two displacement processes occur per revolution.

2#(i#1"' Disp"#$'0'nt 2#n' P,0pAnly the single chamber vane pump is available as a variabledisplacement volume type. By moving the stator &stro$e ring' with anad>ustment screw, it is possible to adapt the si9e of the displacement

chambers. 5hen the a(is of the rotor is in the centre position of the stro$ering, all formed chambers are of equal si9e and the outow of the pump isnil.

hree positioning devices may be used!Hori9ontal ad>ustment screw for the stro$e volume! displacement volume

is directly determined by the distance between the stro$e ring and therotor of the pump.Height ad>ustment screw! this changes the vertical position of the stro$ering which directly aects dynamic response of the pump and noise."etting screw for ma(imum operating pressure! it sets the amount of thespring pre#tensioning that determines the ma(imum operating pressure.he outow of the pump may be controlled and ad>usted mechanically&i.e. directly with an ad>ustment screw on the pump'. Cou can also controlthe outow by other means, such as a combination of hydraulic andelectrical control.

Sin!"' $)#01'( 3#n' p,0pIn a single chamber vane pump, the stro$e movement of the vanes islimited by a ring with a circular internal trac$. he position of this so#called stro$e ring is o#centre with respect to the rotor, resulting inchange of volume in the displacement chambers. he displacementchambers are created by the rotor, two vanes, the internal surface ofthe ring and the control discs on one side.

In a single chamber vane pump, the system pressure is only on oneside of the rotor. his causes a signicant load on the bearings. oreduce this load, the forces acting on the rotor must be in balance.his is the reason why double chamber vane pumps were designed,as mentioned below.


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H%&(#,"i$ Piston P,0psHydraulic piston pumps can handle large ows at

high hydraulic system pressures. ypicalapplications are mobile and constructionequipment, marine au(iliary power, metal formingand stamping, machine tools and oil eldequipment.

In these pumps, the pistons accurately slide bac$and forth inside the cylinders that are part of thehydraulic pump. he sealing properties of the

pistons are e(cellent.

;ey features of hydraulic piston pumps are!

*ompact si9e High power density Aptimum eciency and reliability High speed and torque High operating pressures

Hydraulic piston pumps operate at very highvolumetric eciency levels due to low uid lea$age.

he plungers may consist of valves at the suction andpressure ports or with input and output channels.

=iston pumps with valves at the ports are better suitedto operate at higher system pressures due to bettersealing characteristics.


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he design of an a(ial piston unit is based on two important principles. @irst, thedesign of the a(ial piston pump may be based on the swash plate principle or benta(is design. "econdly, hydraulic system parameters have to be ta$en into account!whether the usage is to ta$e place in an open or closed loop circuit is of greatimportance.

In closed loop circuits, the return line &i.e. the suction line of the pump' is under

pressure. his must be incorporated in the design of a(ial piston units used in closedloop systems. It is also imperative to have a variable displacement volume hydraulicpump in operation in these systems. In (ed displacement volume conguration, thea(ial piston unit can be used both as pump and as motor.

In bent a(is design, the displacement volume is dependent on the swivel angle! thepistons move within the cylinder bores when the shaft rotates. In swash plate design,

the rotating pistons are supported by a swash plateD the angle of the swash platedetermines the piston stro$e.

ypical parameters are!7isplacement vol.! to +,/// cc8a(imum pressure! up to 2/ bar"peed range! +,// to ++,/// rpm

4adial piston pumps are used in applications that involve high pressures&operating pressures above 2// bar and up to ?// bar', such as presses,machines for processing plastic and machine tools that clamp hydraulics.4adial piston pumps are the only pumps capable of wor$ing satisfactorily atsuch high pressures, even under continuous operation.

4adial piston pumps are available in two dierent congurations. 5itheccentric cylinder bloc$, the piston rotates within the rigid e(ternal ring.0ccentricity determines the stro$e of the pistons. Ar, with an eccentric shaft,the rotating eccentric shaft causes radially#oscillating piston movements to beproduced. 8ost models have an odd number of pistons to reduce the owpulsation.

ypical parameters are!7isplacement volume! /. to +// cc8a(imum pressure! up to ?// bar &si9e dependent'4ange of speeds! +,/// to -,/// rpm &si9e dependent'

here are three dierent types of hydraulic piston pumps!

)(ial =iston =umps

4adial =iston =umps


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HYDRAULIC FLUIDS


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H%&(#,"i$ 4,i&s, also called )%&(#,"i$ "i5,i&s,are the medium by which power is transferred inhydraulic machinery. *ommon hydraulic uids arebased on mineral oil or water. 0(amples ofequipment that might use hydraulic uids includee(cavators and bac$hoes, hydraulic bra$es, powersteering systems, transmissions, garbage truc$s,

aircraft ight control systems, lifts and industrialmachinery.Hydraulic systems li$e the ones mentioned abovewill wor$ most eciently if the hydraulic uid

used has 9ero compressibility.


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Hydraulic uids can contain a wide range of chemicalcompounds, including! oils, butanol, esters &e.g. phthalates,li$e 70H=, and adipates, li$e bisethylhe(yl' adipate',polyal$ylene glycols &=)1', organophosphate &e.g.

tributylphosphate', silicones, al$ylated aromatic hydrocarbons,polyalphaolens &=)A' &e.g. polyisobutenes', corrosioninhibitors &incl aci scavengers', anti#erosion additives, etc.0nvironmentally sensitive applications &e.g. farm tractors andmarine dredging' may benet from using 1io&'!(#"'

)%&(#,"i$ 4,i&sbased upon rapeseed &*anola' vegetable oilwhen there is the ris$ of an oil spill from a ruptured oil line.ypically these oils are available as I"A -, I"A 2:, and I"A :Especication oils. )"8 standards )"8#7#://:, 1uide for)ssessing Biodegradability of Hydraulic @luids and )"8#7#

:/2:, "tandard *lassication of Hydraulic @luids for0nvironmental Impact are relevant.


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Because industrial hydraulic systems operate at hundredsto thousands of ="I and temperatures reaching hundreds ofdegrees *elsius, severe in>uries and death can result fromcomponent failures and care must always be ta$en whenperforming maintenance on hydraulic systems.@ire resistance is a property available with speciali9ed uids.5ater#gycol and polyol#ester are some of these speciali9eduids that contain e(cellent thermal and hydrolitic properties,

which aid in re resistance.

"pecial, stringent care is required when handling aircrafthydraulic uid as it is critical to ight safety that it stay free

from contamination. It is also necessary to strictly adhere toauthori9ed references when servicing or repairing anyaircraft system. "amples from aircraft hydraulic systems areta$en during heavy aircraft maintenance chec$s &primarily *and 7 chec$s' to chec$ contamination.


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B4);0 @3FI7

Bra$e uid is a subtype of hydraulic uid with highboiling point, both when new &specied by theequilibrium boiling point' and after absorption ofwater vapor &specied by wet boiling point'. Fnderthe heat of bra$ing, both free water and water vaporin a bra$ing system can boil into a compressiblevapor, resulting in bra$e failure. 1lycol#ether baseduids are hygroscopic, and absorbed moisture will

greatly reduce the boiling point over time. "iliconebased uids are not hygroscopic.

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