Hydraulics System

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What are the Basic Principles Of Hydraulics?Pascal's Law states that the "Pressure applied to any part of a confined fluid transmits to every other part with no loss. The pressure acts with equal force on all

equal areas of the confining walls and perpendicular to the walls. This is the basic principle for any hydraulic system."

Introduction:

Earlier, weights werelifted using pulleys,levers, bloc and tacles, etc. !ovements for a ships rudder or steering a vehicle where achieved by mechanical linages

lie cams, levers, couplings, and gears which made the system complicated. These manual or mechanical methods of operation had several limitations. They also

involved huge man power and long woring hours for a particular #ob. $s the population and technology increased e%ponentially, the demand for quicer and

easier to operate equipment increased. To cater to this need, hydraulic machines were introduced.

Basic Hydraulic Principles


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$ simple hydraulic system consists of hydraulic fluid, pistons or rams, cylinders, accumulator or oil reservoir, a complete

woring mechanism, and safety devices. These systems are capable of remotely controlling a wide variety of equipment

by transmitting force, carried by the hydraulic fluid, in a confined medium. !odern developments in hydraulics have

involved many fields in engineering and transportation. These systems transfer high forces rapidly and accurately even in

small pipes of light weight, small si&e, any shape, and over a long distance. These systems play a vital role from small

car's steering to super sonic aircrafts maneuvering devices. !ore powerful and accurate systems are also used in

maneuvering huge ships.

Pascals Law:

Pascal's Law, framed by laise Pascal, states that (Pressure applied to any part of aconfined fluid transmits to every other

part with no loss. The pressure acts with equal force on all equal areas of the confining walls and perpendicular to the

walls." This is the basic principle for any hydraulic system.

Hydraulic Pressure & Force:

Pressure can be defined as (the force acting on unit area, applied in a direction perpendicular to the surface of the ob#ect".

Pressure ) *orce+ $rea.

o, hydraulic pressure can be stated as the force e%erted by a fluid on unit area, anywhere on the surface within the

container.

A i!ple Hydraulic yste!:


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A closed toothpaste tu"e can "e considered as an e#a!ple for a si!ple hydraulic syste!$ %he toothpaste can "e

considered as a hydraulic fluid worin' inside the syste! which is confined$ Four or fi(e holes are !ade on the

tu"e$ By eepin' the cap of the toothpaste tu"e closed) apply pressure at a particular point on the tu"e$ %his

!aes the toothpaste to co!e out fro! all the holes e(enly$ %his is a si!ple e#a!ple to understand Pascals law$

%hus force applied at a particular point on a fluid in closed syste!) transfers e*ual force on all other parts of the

syste!$ Further) the force acts perpendicular to the walls of the confined area$

Other e#a!ple is the hydraulic "raes used in auto!o"iles$ %he dri(er applies force at the "rea pedal +one

particular point on fluid in closed syste!,) thus trans!ittin' this force onto the hydraulic fluid under the piston

+"rea pedal,) transfers e*ual force to all other "rae shoes) thus stoppin' the (ehicle$

%here are se(eral other areas where hydraulics are applied$ %hey are:

-$ Auto!o"ile 'ara'e


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-ydraulic raing ystem $utomobile/

Hydraulic Brain' yste!

$ hydraulic braing system transmits brae0pedal force to the wheel braes through pressuri&ed fluid, converting the fluid

pressure into useful wor of braing at the wheels. $ simple, single0line hydraulic layout used to operate a drum and disc

brae system is illustrated in *ig. 12.34. The brae pedal relays the drivers foot effort to the master0cylinder piston, which

compresses the brae fluid. This fluid pressure is equally transmitted throughout the fluid to the front disc0caliper pistons

and to the rear wheel0cylinder pistons. $s per the regulations a separate mechanical paring brae must be incorporated

with at least two wheels. This provision also allows the driver to stop the vehicle in the event of failure of the hydraulic

brae system.

Fi'$ ./$01$ Hydraulic sin'le2line "rain' syste!$


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5n a hydraulic braing system the braing force is directly proportional to the ratio of the master0cylinder cross0sectional

area to the disc or drum0brae wheel0cylinder cross0sectional areas. Therefore these cylinder diameters are appropriately

chosen to produce the desired braing effect. The wheel0cylinder cross0sectional areas of the front and rear disc0and

drum0braes respectively may be chosen to produce the best front0to0rear braing ratio. -ydraulic fluid is incompressibleprovided there is no trapped air in the system. 5f air is present in the braing circuit, the foot0brae movement becomes

spongy. 5n a hydraulic system the internal

friction e%ists only between the cylinder pistons and seals. The friction is caused by the fluid pressure squee&ing the seal

lips against the cylinder walls as the piston moves along its stroe. $ hydraulic braing system is suitable only for

intermittent braing applications, and a separate mechanical linage must be incorporated for paring braes.

The hydraulic system offers the following advantages over the mechanical layout, a/ This provides equal braing effort on

all wheels. 4/ This requires relatively less braing effort to deliver the same output.

c/ This is a fully compensated system so that each brae receives its full share of the pedal effort.

d/ The efficiency of the hydraulic system is greater than that of the mechanical layout.

e/ This system is suitable for vehicles having independent suspension.

+/ 5t is easy to alter thrust on shoe because the force e%erted on a piston depends on the piston area. The larger the area,

the greater the thrust on the trailing shoe, so a larger piston can be used.

3arious 4o!ponents

6arious components and their functions in a hydraulic braing system are as follows.


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Brae Pipes$

These are steel pipes which form part of the fluid circuit between the master0cylinder and the wheel0cylinders. These

pipes transfer the fluid along the body structure and rigid a%le members. *le%ible hoses connect the sprung body pipes tothe unsprung a%le wheel0brae units, to allow for movement *ig. 12.34/.

5aster2cylinder$

This converts foot0pedal force to hydraulic pressure within the fluid system by means of the cylinder and piston *ig.

12.34/.

6isc2"rae$

This comprises of a disc bolted to the wheel hub. This is sandwiched between two pistons and friction pads. The friction

pads are supported in a caliper fi%ed to the stub0a%le *ig. 12.34/. 7hen the braes are applied, the pistons clamp the

friction pads against the two side faces to the disc.

6ru!2"rae$

This uses two brae0shoes and linings supported on a bac0plate. The bac0plate is bolted to the a%le0casing. These

shoes pivot at one end on anchor pins or abutments attached to the bac0plate *ig. 12.34/. The other free ends of theboth shoes are forced apart when the braes are applied. The shoes e%pand radially against a brae0drum positioned

concentrically on the wheel hub.

Wheel2cylinders$

$s the hydraulic line pressure acts on the cross0sectional area of the disc and drum cylinder pistons *ig. 12.34/ in wheel

cylinders, the hydraulic pressure is converted into braing effort. This braing effort either presses the friction pads against


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the side faces of the disc or forces the shoe friction linings against the inside of the drum.

./$/$.$

%he 5echanics of a Hydraulic Brain' yste!

To appreciate the machines of the hydraulic braing system, a simple analysis is presented to show how a suitable force

ratio is obtained between the foot0pedal and the wheel0cylinder pistons. $ braing system shown in *ig. 12.34 is

considered.


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Brae 5aster cylinders

The brae master0cylinder contains a cylinder and a piston whose function is to produce hydraulic pressure in the

pipeline. This pressure is subsequently converted to force to actuate the wheel0cylinder disc0pads or shoe0e%panders. The

master cylinders are either i/ residual0pressure type or 8/ non0residual0pressure type.

%he Basic Principle Of HydraulicsThe principle of hydraulics is based on Pascal's famous theory. 5t states the pressure of the liquid produced in an enclosed structure has the

capacity of releasing a force up to ten times the pressure that was produced earlier.

Through hydraulics, the basic result to be achieved is that with little pressure, a great force should be produced.

%he 7(olution Has Be'un

7ith the invention of hydraulics lift its, you can actually mae your car dance. These cars are popularly called as the "lowriders".

They are named for a specific reason. These cars are custom0 made to ride very low to the ground. The hydraulic systems installed in these cars

mae them hop around by raising and lowering these cars. To mae these cars loo lie they're hopping, the hydraulic systems also demand the

installation of 91 to :2 volts -ydraulic Pumps. These hydraulic inventions can be seen in movies lie The *ast and the *urious and in some

lowriding competitions.

How %he Basic yste! Wors


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The woring of a hydraulic system is very simple. The basic fluid used in this system is oil. $ hydraulic

machine has two or more cylinders that are connected to a single pipe containing the oil and the

pistons that helps in pushing the fluids in the cylinders. Even the car braes are based on the hydraulic system.

7hen you apply your car braes, your brae pedal maes the piston to act and apply force on the master ;ylinder.

The main pipe is connected to four slave pistons that activate the brae pads of your car to the brae rotor, which in turn maes the car come to a

stop. The basic hydraulic components are as follows in flange gas%ets in pipelines. Tightening a bolt too much can cause immense stress

that can eventually lead to bolt brea%age.

From the discussions above' the importance of precision required in bolting operations becomes very clear.

/ydraulic torque wrenches provide the means of near perfect control of tightening torque ma%ing them tools

of choice as compared to other uncontrolled methods of bolt tightening such as sledge hammers and stri%ing

wrenches or pneumatic wrenches that are devices with limited control.


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The 7oring $nd Bsage Af -ydraulic Press$ hydraulic press is a machine that has a bed or a plate in which the metallic material is placed so that it can be crushed, straightened

or moulded.


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All Of It 5ade Possi"le With %he Hydraulic PressThe concept of the hydraulic press is based on Pascal's theory, which states that when pressure is applied on fluids in an enclosed

system, the pressure throughout the system always remains constant. 5n simple words, a hydraulic press is a machine that maes

use of the pressure e%erted on the fluids to crush something.

Coseph ramah invented the hydraulic press, hence it is also nown as the ramah Press.

How the Hydraulic Press wors

ince the hydraulic press wors on the basis of Pascal's Law, its woring is similar to the one of the hydraulic system. $ hydraulic

press consists of basic components used in a hydraulic system that includes the cylinder, pistons, the hydraulic pipes, etc.The

woring of this press is very simple. The system comprises of two cylinders, the fluid usually oil/ is poured in the cylinder having a

small diameter. This cylinder is nown as the slave cylinder.

The piston in this cylinder is pushed so that it compresses the fluid in it that flows through a pipe into the larger cylinder. The larger

cylinder is nown as the master cylinder. The pressure is e%erted on the larger cylinder and the piston in the master cylinder pushesthe fluid bac to the original cylinder.

The force applied on the fluids by the smaller cylinder results in a larger force when pushed

in the master cylinder. The hydraulic press is mostly used for industrial purposes where a

large pressure is required for compressing metals into thin sheets. $n industrial hydraulic

press uses the material to be wored upon along with the help of the press plates to crush

or punch the material into a thin sheet.

8ses Of A Hydraulic Press

$ hydraulic press is used for almost all industrial purposes. ut basically it is used for transforming metallic ob#ects into sheets of

metal. 5n other industries, it is used for the thinning of glass, maing powders in case of the cosmetic industry and for forming the

tablets for medical use. The other common uses of the hydraulic presses are as follows??? revolutions per minute.

The si&e advantage can be gauged from the fact that the si&e of a >hp hydraulic motor will

be roughly that of a 3>?ml beer can. 5n addition, there would be very low level noise andvibration generation and much higher efficiency. -LT and L-T hydraulic motors are

available in different types.

Three types that find popular use are piston, gear and vane type hydraulic motors. Piston motors, which use reciprocating pistons to

transmit energy to the worload, are basically of two types.

a$ A#ial piston !otors

"$ ;adial piston !otors

The a%ial piston motor is of the 'swashplate type' and has a ban of cylinders arranged in a circle 34? degrees/ parallel to each other.

Each cylinder has a piston, which reciprocates with one end of the piston pushing against an eccentric swash0plate located at one

end of the ban of cylinders. There is a mechanical arrangement through which the eccentric plate is connected to an output shaft

that is a%ially aligned with the cylinders. Guring motor operation, the cylinders are filled with high0pressure hydraulic fluid in a

particular sequence maing the pistons move outwards to push sequentially against the swash0plate causing it to rotate. An the

return stroe of the piston the fluid is swept bac at low pressure to return to a reservoir. The operation imparts rotational movement


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to the output shaft, of which one end is connected to the swash0plate and other to the worload. This is a design that caters to a very

compact cylindrical hydraulic motor. !ost a%ial hydraulic motors are -LT.

$ radial piston hydraulic motor has a ban of cylinders arranged lie a car engine with a series of pistons riding on cams along a

camshaft, which is attached to the output shaft. The reciprocating movement of the pistons gives rotary movement to the

camshaft+output shaft that is tapped for power. 5n another variation cylinders are arranged radially lie that of an aircraft engine withthe pistons moving inwards to push against a cam located in center causing it to rotate. The cam is mechanically lined to the output

shaft+worload. @et another type of radial piston hydraulic motor with cylinders placed radially lie an aircraft engine has the pistons

moving outwards to push against cams in a housing that surrounds the motor. This maes the housing rotate. The rotating housing is

tapped for power. These motors are generally used as wheel motors and for other suitable applications lie forlifts etc.

Hear type hydraulic motors can be classified as internal gear or 'gerator' type and e%ternal gear motors. Herator motors are very quiet

in operation and designed to transmit rotary power through an output shaft connected to a rotor moving inside an outer stator. upply

of hydraulic fluid under pressure maes the rotor move eccentrically along the inner periphery of the stator. $n e%ternal gear hydraulic

motor has a set of meshing gears enclosed in a sealed housing have passages supply and return of hydraulic fluid. Pressuri&ed

hydraulic fluid flowing into the housing has an action on the gear teeth and maes the gears rotate. The rotational movement of thegears is transmitted to the worload through an output shaft connected to the rotating gears and passing through the motor housing.

6ane type hydraulic motors have movable vanes connected to a centrally located output shaft. The whole arrangement is enclosed in

a housing+ case that receives hydraulic fluid under pressure from the pump. This fluid e%erts force of the vanes to mae them move

lie fan blades. This action results in rotating the output shaft, which is tapped for power.

Hydraulic 5otor Applications

-ydraulic motors are mainly used in construction and agricultural equipment. They can be commonly seen in heavy earth moving

equipment lie e%cavators, sids, forlifts, heavy dumper trucs, bulldo&ers etc. where hydraulic cylinders e%tend and retract as vital

operational parts while the machine performs various wor. These cylinders are hydraulic motors transmitting linear power.

Gue to the high torque at low speeds, loaders and other construction equipment use heavy hydraulic motors to drive the wheels for

moving the machines around. There is one motor for each wheel and the diesel engine is used to drive the pump, which deliver

hydraulic fluid to the motors. $ hydraulic motor with the right specifications needs to be fitted to enable the machine to function

properly.

Gue to the very heavy loads imposed on car crushers, hydraulic motors are the preferred power delivery system. 7hen the machine

stalls' due to something 'uncrushable' creating a snag, the building pressure inside the supply circuit of the hydraulic operates a

pressure relief valve preset to a specific pressure to return the supply of the fluid bac to the reservoir. 5t also triggers a mechanism to


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reverse the direction of rotation to release the snagging materiel and free the machine after which normal rotational direction is

resumed. $n electric motor would either trip or burn out.

;ompact and e%tremely efficient, small hydraulic motors can be used for various machining operations lie boring, reaming, drilling

etc. Gue to their small si&e they are tools of choice for applications lie

Hydraulics System

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