UNIT-1

FLUID POWER SYSTEMS AND FUNDAMENTALS

PART-A

1. Name any four desirable characteristics of hydraulic pumps.[MAY/JUNE-2009]

Pumps should provide safe and maximum system working pressure.

They should have high volumetric and overall efficiency.

They should be compact and also have higher power to weight ratio.

They should possess the variable displacement control

2. Name any four drawbacks of fluid power systems.[APR/MAY-2005]

Hydraulic fluid leakage poses many problems to the operations as well as operators.

Flammable hydraulic fluids may possess fire hazards thus limiting the upper level of working temperature.

Hydraulic elements require special treatments to protect them against rust,corrosion,dirt etc. otherwise the contaminated elements may impair the system operation.

Hydraulic fluids may pose problems if it disintegrates due to ageing and chemical deterioration.

3. Define fluid power.[NOV/DEC-2005]

Fluid power is defined as the technology that deals with generation,control and transmission of power using pressurized fluids.

4. How do you classify direction control valves?[NOV/DEC-2005}

Based on the number of ports present the DCV’s are classified as

Two way valve

Three way valve

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Four way valve

5. Define viscosity and bulk modulus of a hydraulic fluid.[MAY/JUNE-2006]

Viscosity:It may be defined as the shearing force required to move two plane surfaces relative to one another with a film of fluid between them.

Bulk Modulus:It is the measure of compressibility of a fluid.It is the reciprocal of compressibility.

6. Give the expression used to determine the wall thickness and inside diameter of a hydraulic conductor.[MAY/JUNE-2006]

Wall Thickness,t=(Do-Di)/2

Inside diameter of a hydraulic conductor,

Where Do= Conductor outside diameter

A= Required pipe flow area

7. Define friction factor.[NOV/DEC-2005]

Friction factor is a dimensionless number required to calculate the energy losses due to friction in the pipe.

For laminar flow, the friction factor, f, is a function of Reynolds number only where as for turbulent flow f is a function of Reynolds number as well as the relative roughness of the pipe.

8. Differentiate pressure compensated and non-pressure compensated pumps.[NOV/DEC-2006]

In pressure compensated pump,the pump flow can be made to zero.Such a pump has its own protection against excessive pressure build up.Also there is no power waste and reduced fluid heading.whereas non-pressure compensated pumps are hydraulically unbalanced and cause undesirable side load on the bearing side of the pump.

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17. Under what conditions pneumatic systems are preferred. [AU-NOV/DEC-2012]

Pneumatic systems are often used instead because pneumatic pressure is usually cheaper to obtain, since most industrial facilities already have compressed air available. Since many systems does not require extremely high forces, and only need to make movements from one position to another, and doesn’t need to stop in between, pneumatics is the easier and cheaper way to go

18. List the primary functions of hydraulic fluid? [AU-NOV/DEC-2012]

To transmit fluid power efficiently to perform useful work.

To lubricate the moving parts to minimize wear and friction.

To absorb, carry and dissipate the heat generated with in the system.

To seal the close clearances between mating parts against leakage.

To prevent the rusting or corrosion.

To rapidly settle and separate the insoluble contaminants and abrasion.

19. State Pascal’s law with an industrial example [AU-MAY/JUNE-2012]

Pascal’s law states that the pressure generated at any point in a confined fluid acts equally in all directions.

Applications: Bramah’s hydraulic press and Air to hydraulic pressure booster.

20. Give Darcy’s equation to calculate head loss in pipe. [AU-MAY/JUNE-2012;2014]

HL=f*L*V2

D*2g

21. List the applications of fluid power in agriculture and aviation industries. [AU-MAY/JUNE-2013]

Agriculture: Hydraulically driven farm equipments

Aviation: Hydraulic retractable landing wheels3

22. Compare hydraulic and pneumatic drives for automation [AU-MAY/JUNE-2012]

S.No Hydraulic System Pneumatic system

1 It employs a pressurized liquid as a fluid

It employs a compressed gas usually air as a fluid.

2 Hydraulic systems are designed as closed system

Pneumatic systems are usually designed as open system.

3 System get slow down if leakage occurs

Leakage does not affect the system much more.

4 Valve operations are difficult Easy to operate the valves

5 Heavier in weight Light in weight

6 Pumps are used to provide pressurized liquid.

Compressors are used to provide compressed gas.

7 System is unsafe to fire hazards

System is free from fire hazards

8 Automatic lubrication is provided

Special arrangements are made for lubricating the parts.

23. Write the procedure to calculate the pressure drop in hydraulic circuits. [AU-MAY/JUNE-2013]

ΔP=woil*HL

HL= 64*L*V2

Re*D*2g

woil= Specific gravity*wwater

24. Name the different types of fluid power systems. [AU-APR/MAY-2011]

Hydraulic power system4

Pneumatic power system

25. Give any four important properties of hydraulic fluids. [AU-APR/MAY-2011]

Good lubricity

Stable viscosity characteristics

High bulk modulus and degree of incompressibility

Good heat dissipation capability.

26.Give the advantages of fluid power system.(N/D-2013)

Ease and accuracy of control

Multiplication of force

Constant force or torque

Simplicity,safety,economy

27.Draw the symbol of pressure relief valve.(N/D-2013)

28.What is the importance of Reynolds number?(M/J-2014)

If Reynolds number (Re)<2000,then the flow in pipes is laminar.

If Reynolds number (Re)>4000,then the flow in pipes is turbulent.

If Reynolds number is between 2000 and 4000 then the flow in pipes is unpredictable

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PART-B

1. Explain the advantages of fluid power?(APR/MAY- 2008;MAY/JUNE- 2009)

Advantage of fluid power

It is reckoned that the future industries will depend largely upon automation to increase productivity. The activities associated with automation include remote and direct control of production operations manufacturing process, and materials handling. In this regard, the fluid power is considered as the muscle of automation because it offers many advantage as shown below.

*Ease and accuracy of control:

With the use of simple levels and or push buttons the fluid power system can facilitate easy starting, stopping, speeding up or slowing down and positioning force that provide any desired power.

*Multiplication of force:

The fluid power system can multiply force (in the order of 10^2 to 10^5 times) easily and efficiently.

*Constant force or torque:

The fluid power system is the only system which can provide constant force or torque irrespective of variations in speed ,whether the work output moves a few millimeters per min, several meters per min,or thousands of revolutions per min.

*Simlicity,safety,economy:

When compared to electrical and mechanical system, generally the fluid power system uses fewer moving parts. That”s why they are simple to maintain and operate as s result, it also maximizes safety, compactness and reliability.

*other benefits:

Some of the other advantages of using the fluid power system include:

i) High power to weight ratio.ii) Instant reversal of motion with accuracy is possible.iii) Automatic protection against overloads.

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iv) Infinitely variable control(of output force output torque and output speed).

v) Requires lesser space.vi) Relatively smooth and quiet operation.vii) Greater efficiency(about 85-90) and economy due to low friction

losses.viii) Low inertia and ease of shock absorption(during actuator

motion,reversal,start,and stop)

2.Describe the applications of fluid power system and list the main components required for a power pack with circuit. List out the application of fluid power.(APR/MAY-2008;N/D-2013)

S.NO INDUSTRY/FIELD APPLICATIONS

1 Manufacturing industry Hydraulic presses, pneumatic hand tools, hydraulic and pneumatic fixtures, automatic and semi-automatic operating machines such as machines with hydraulic feed, pneumatic drive,automatic andexing machine ,hydraulic driven die casting machine,hydraulic feed macine,automatic lathe with air-operated equipment,hydraulically operated shaving machine,cutting machine,drilling machine ect.

2 Automobile industry Welding equipments using hydraulic controls, hydraulic brakes, automotive transmissions,power steering,power breaks,air conditioning lubrication,water coolent,and gasoline pumping systems.

3 Naval industry Fluid power used for cargo 7

handling,winches,propeller,pitch control,submarine control system operating of shipboard aircraft elevators and drive systems for radar and sonar.

4 Agriculture industry Hydraulic and pneumatic diven elevator conveyors for use in harvesting of grains,fluid power driven farm equipments.

5 Aviation and Aerospace industry Hydraulic activated landing gears cargo doors,gear drives and flight controls drives such as rudders ,ailerons and elevator for the aircraft,fluid powered missile launching system.

6 Mechatronics field Fluid logic components,servo-controlled pneumatic actuators in robotics and tactile sensing,fluid power used for operating various mechatronics elements such as a spindle drives ,automatic tool clamping, tool magazines and automatic tool charges ect..

7 Construction field Fluid power driven earth moving equipments,fluid power drivers, brush drive used for cleaning roads,floors etc…

Main components required for a power pack:

Tank/Reservoir;Filter;Hydraulic pump;Motor;Pressure regulator;Piping;Valves and actuators.

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Working:

How does a hydraulic cylinder (Actuator) work?

The schematic arrangement of the hydraulic cylinder is shown in fig.It consists of a movable piston connected to the output shaft and two parts A and B.If a liquid is pumped through port A,then the piston will move up and if a liquid is pumped through port B,then the piston will move down.Obviously when the pressurized liquid is pumped at one side of the piston.Then the non-pressurized liquid on the other side of the piston must be retrieved back to the liquid tank.

Working of the total hydraulic system:

The total hydraulic system for the task moving a weight(W) by a distance (D) is shown in fig.The parts enclosed in the dotted-lined box are common to an area of the plant which have many linear and rotary hydraulic actuators.In these case,we use only one linear hydraulic actuator.

AC induction motor(M) drives the hydraulic pump(P),so that the fluid is pumped from the tank at the required pressure.The fluid circulated into the system should be clean to reduce the wear of the pump and cylinder,hence a filter is used immediate to the storage tank.Since the pump delivers constant volume of fluid for each revolution of the shaft,the fluid pressure rises indefinitely,until a pipe or pump itself fails.To avoid this,same kind of pressure regulator is used to spill out the excess fluid back to the tank.

Cylinder movement is controlled by a 3 position control valve.One side of the valve is connected to a pressurized fluid line and the fluid retrieval line;and the other side of the valve is connected to a Port A and port B of the cylinder.Since the hydraulic circuit is a closed one,the liquid transferred from the storage tank to one side of the piston,and the fluid at the other side of the piston is retrieved back to the tank.

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3.Explain the working principle of hydraulic system with neat sketch and its advantage?.[NOV/DEC-2006,2007,2013;M/J-2014]

Basic components of a hydraulic system:

Reservoir(or tank);Pump;Prime mover;Valves;Actuator;Fluid transfer piping.

Working:

How does a hydraulic cylinder (Actuator) work?

The schematic arrangement of the hydraulic cylinder is shown in fig.It consists of a movable piston connected to the output shaft and two parts A and B.If a liquid is pumped through port A,then the piston will move up and if a liquid is pumped through port B,then the piston will move down.Obviously when the pressurized liquid is pumped at one side of the piston.Then the non-pressurized liquid on the other side of the piston must be retrieved back to the liquid tank.

Working of the total hydraulic system:

The total hydraulic system for the task moving a weight(W) by a distance (D) is shown in fig.The parts enclosed in the dotted-lined box are common to an area of the plant which have many linear and rotary hydraulic actuators.In these case,we use only one linear hydraulic actuator.

AC induction motor(M) drives the hydraulic pump(P),so that the fluid is pumped from the tank at the required pressure.The fluid circulated into the system should be clean to reduce the wear of the pump and cylinder,hence a filter is used immediate to the storage tank.Since the pump delivers constant volume of fluid for each revolution of the shaft,the fluid pressure rises indefinitely,until a pipe or pump itself fails.To avoid this,same kind of pressure regulator is used to spill out the excess fluid back to the tank.

Cylinder movement is controlled by a 3 position control valve.One side of the valve is connected to a pressurized fluid line and the fluid retrieval line;and the other side of the valve is connected to a Port A and port B of the

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cylinder.Since the hydraulic circuit is a closed one,the liquid transferred from the storage tank to one side of the piston,and the fluid at the other side of the piston is retrieved back to the tank.

Advantages:

Large load Capacity;High accuracy and precision;Smooth movement;Automatic lubricating provision to reducen wear;Division and distribution of hydraulic power is simple and easier;Limiting and balancing of hydraulic power are easy to perform.

4.With neat sketch describe the working principle of pneumatic power system?[NOV/DEC-2006;N/D-2013]

Pneumatic power system

Basic components of a pneumatic system:

Reservoir(or air tank);Compressor;Prime mover;Valves;Actuator;Fluid-transfer piping.

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Working:

The total pneumatic system for the task of lifting a weight (W) by a distance(D) is shown in fig.The parts enclosed in dotted-lined box are common to an area of the plant,which may have many linear and rotary actuators.In this case we use only one linear hydraulic actuator.

Air is drawn from the atmosphere through the air filter and raised to the required pressure by an air compressor.Air contains significant amount of water vapour and also the air temperature is raised considerably by the compressor.So the air must be cooled before using it in the system,which results in condensation.

The compressed air is stored in the reservoir,which has a water outlet at the bottom of the reservoir and a pressure switch(PSI) to control the pressure of the compressed air(by controlling the motor).Pressure switch stops the motor when the required pressure is attained and starts the motor when the pressure falls down the mark.

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The outlet of the reservoir is connected to a component called F.R.L.(Filter-Regulator-Lubricator) unit,which does the following activities:

1.Filters the tiny foreign particles from the compressed air2.Regulates the pressure just before entering the system3.Lubricates the compressed air for the pneumatic cylinders.

The cylinder movement is controlled by the pneumatic valve.one side of the pneumatic valve is connected to the compressed air line and silencers for the exhaust air and the other side of the valve is connected to port A and port B of the cylinder.

Advantages:

Light density of air and hence low inertia effect of pneumatic components;Light system weight;Comparatively easy operation of valves;Power losses and leakages are less;Low cost.

5.Enumerate and briefly discuss the properties and factors considered for selection of oils/List out the some properties of fluid.[NOV/DEC-2006,2007;M/J-2014]

Physical properties of Fluid:

Density;Viscosity;Capillarity;Cavitation;Compressibility and Bulk modulus

Density:

The density of a fluid is that quantity of a matter contained in the unit volume of the substance.

The density can be expressed as different types

Mass Density:

Mass density also known as specific mass or simply density is defined as mass of the fluid per unit volume.

Formula:

Units: (N/m3)14

Dimension; ML-2T-2

Typical value: Wwater=9.81*103 N/m3

Woil=12.07 N/m3

Weight density:

It is also known as specific weight,is defined as the weight per unit volume.

W=ρ*g

Specific gravity:

It is also known as relative density,is defined as the ratio of mass density of a fluid to mass density of a standard fluid.

Specific volume:

It is defined as the reciprocal of mass density.

Viscosity:

Concept:

Viscosity is the most important property of the fluid.Viscosity is the measure of the ability of a fluid to flow.It is measured of the fluid,internal resistance to shear or flow as a definite temperature and pressure.

Definition:

Viscosity is defined as the shearing force required to move two plane surface relative to one another with a film of fluid between them.

Absolute viscosity or Coefficient of dynamic viscosity:

This law states that the shear stress on a fluid element is directly proportional to the shear strain.The constant of proportionality is called the co-efficient of viscosity

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Kinematic Viscosity:

It is defined as the ratio of dynamic viscosity to mass density.

Viscosity index:

The viscosity index of a liquid is a number indicating the effect of a change in temperature on viscosity.

Cohesion and Adhesion:

Cohesion:It means intermolecular attraction between molecules of the same liquid.It enables a liquid to resist small amount of tensile stresses.Cohesion is an tendency of the liquid to remain as one assemblage of particles

Adhesion:It means the attraction between the molecules of a liquid and the molecules of a solid boundary surface in contact with the liquid.This property enables the liquid to stick to another body.

Surface Tension:

A liquid,being unable to expand freely,will form an interface with a second liquid or gas.Molecules deep within the liquid repel each other because of their close packing.Molecules at the surface are less dense and attract each other.When half of their neighbours are missing the mechanical effect is that surface is in tension.

Capillarity:

Capillarity is a phenomenon by which a liquid (depending upon its specific gravity rises into a thin glass tube above or below its general level.

The phenomenon is due to the combined effects of cohesion and adhesion of liquid particles.

Cavitation:

When the liquid pressure is dropped below the vapour pressure due to flow phenomenon,then there will be local boiling and a cloud of vapour bubbles will form,this phenomenon is known as cavitation.

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Cavitation causes serious damage in almost any component in a hydraulic system.Cavitation cn affect the performance of hydraulic machinery such as pumps,turbines and propellers.

Compressibility:

All fluids are compressible to some extent.Compressibility of a liquid causes the liquid to act much like stiff spring.

Coefficient of compressibility:

It is defined as the fractional change in unit volume of liquid per unit change of pressure.

Compressibility,

Where, ΔV=Change in volume

V=Original volume

ΔP=Change in pressure

Generally it is desirable to have the hydraulic fluid which has the minimum compressibility.That is fluid with minimum compressibility will be more stiffer.

Bulk modulus:

Reciprocal of the compressibility,

The higher bulk modulus,the less elastic,more stiffer the liquid.Usually high bulk modulus values are desirable since they result in more stable and less elastic system.

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Required properties of a good hydraulic fluid:

Stable viscosity characteristics

Good lubricity,flammability,demulsibility

Compatibility with system materials.

Stable physical and chemical properties.

Good heat dissipation capability,oxidation stability

High bulk modulus and degree of incompressibility.

Adequate low temperature properties.

Low volatility,density,specific gravity,coefficient of expansion

Simple and ease handling

Inexpensive.

6.Briefly discuss the various types of oils used in power hydraulic systems/Explain the types of hydraulic fluid with advantages and disadvantages;[NOV/DEC;APR/MAY-2008;2014]

Now a days the wide range of hydraulic fluid are used in industrie,because of the wide vastly different areas of application.The hydraulic fluids have been classified by many different systems,based on the different characteristics such as a physical properties,chemical types,operating capabilities,utility or specific applications.

It is separated into two classes

1) Petroleum based on hydraulic oils2) Non petroleum based hydraulic oils

a. Waterb. Emulsionsc. Glycolsd. Water glycolse. Phosphate esters

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PETROLEUM OILS:

Description:

Petroleum based on hydraulic fluid were among the first liquids employed as hydraulic or power transmission fluids

The typical petroleum oils include,Naphthenes,aromatics,paraffins,wax and olefin

Advantage:

Good lubricating characteristics Protection against rust,sludge,corrosion. Longer life Better heat dissipating capability Better sealing property High viscosity index(approximately 100)

Disadvantage:

Low fire resistance Tendency to oxidize rapidly.

WATER:

Description:

Most probably water is the least expensive hydraulic available.Water is treated with chemicals before being used in a fluid power system.The treatment removes undesirable contaminants.Water is also passed through a striner to remove any solid particles.

Advantage;

1. Inexpensive

2. Available in abundance

3. Ideal fire resistant fluid

Disadvantage;

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1. Does not posses lubricating property

2. Highly corrosive in nature

EMULSIONS:

Description:

Emulsions are water oil mixture.The emulsions are available in to general type(oil in water and water in oil) emulsions.

Advantage:

1. Emulsion stability

2. Film strength,good system cooling

3. High viscosity index

Disadvantage:

1. Depletion of water due to evaporation it will reduce viscosity

2. Demulsification may be regular problem water in emulsion.

GLYCOLS:

Description:

The glycols are often by several names such as polyglycols,polyalkalene,glycols and polyethers.

The glycols are extensively used as base stocks and as a component for synthetic lubricants and heavy duty brake fluids.

Advantage:

1. High flash point

2. Very good solubility characteristics

3. Wide range of viscosity

4. High viscosity indices(upto 150)

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Disadvantage:

1. Poor high temperature oxidation properties

2. Not good fire resistant

WATER GLYCOLS:

Description:

Water glycols contains 35-60% water,glycol and a water soluble thickener to improve viscosity.Fire resistant

Advantage:

1. Better fire resistant

2. Less expensive

3. Compatible with most pipe compounds and seals.

Disadvantage;

1. Fairly low viscosity

2. Poor corrosion resistance

3. Not suitable for high pressure and loads.

PHOSPHATE ESTERS:

Description:

Phosphate esters result from the incorporation of phosphorous into organic molecules.Besides as hydraulic fluids they can also be used as a base stock as a part of the base stock or as an additive.

Advantage:

1. Excellent lubricant

2. Excellent oxidation stability

3. Good viscosity-temperature characteristics

4. Good fire resistant property

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Disadvantage:

1. Fairly expensive

2. High acidity causes corrosion and accelerate the rate of hydrolysis leading to deposit formation

PROBLEMS:

On mass density ,weight density and specific gravity[APR/MAY-2005]

7. A tank truck contains 90,000 litre of a hydraulic fluid having a specific gravity of 0.9.Determine the fluids weight density,mass density,specific volume and weight

Given data:

V=90,000 lit=90000*10-3 m3;Specific gravity=0.9

Solution:

To find weight density(ω):

Wfluid=wwater*sp.gravity

Wfluid=9810*0.9

W fluid=8.829 N/m3

To find mass density:

ω =ρ*g

8.829=ρ*9.81

ρfluid=900 kg/m3

To find specific volume:

Specific volume=1/ρ=1/900=1.11*10-3 m3/kg

To find weight(W):22

W=V*ω

= 90000*10-3*8829 W=794.6 KN

ON BULK MODULUS:

8. A 350 cm3 sample of oil is compressed in a cylinder until its pressure is increased from 1 atm to 40 atm.If the bulk modulus equals 1500 Mpa.Find the change in volume of the oil.[MAY/JUNE-2006]

Given data:

V=350 cm3

P1=1atm=1 bar

P2=40 atm=40 bar

ΔP=P1-P2=39 bar=39*105 N/m2

K=1500 Mpa=1500*106 N/m2

Solution:

= -0.91 cm3

% decrease in volume,

= 0.26%

Highly incompressible

9. Write short notes on the following [AU-NOV/DEC-2012]23

1. Laminar and Turbulent flow

2. Darcy-weisbach equation

Laminar and Turbulent flow:

Laminar flow

A laminar flow is one in which paths taken by the individual particles do not cross one another and move along well defined paths.

The laminar flow is characterized by the fluid flowing in smooth layers of laminate.This type of flow is also known as streamline or viscous flow, because the particles of fluid moving in an orderly manner and retaining the same relative positions in successive cross-sections.

Examples:

Flow of oil in measuring instruments Flow of blood in veins and arteries Rise of water in plants through their roots.

Turbulent flow

A Turbulent flow is that flow in which fluid particles move in a zigzag way.

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The turbulent flow is characterized by continuous small fluctuations in the magnitude and direction of the velocity of the fluid particles.

Causes: The turbulence in the fluid may cause

1. More resistance to flow.

2.Greaterenergy loss

3.Increased fluid temperature due to greater energy loss.

Examples:

High velocity flow in a pipe of large size. Nearly all fluid flow problems encountered in engineering practice have a turbulent character

2.Darcy-weisbach equation

The major energy lossesi.e the energy losses due to friction in the pipe can be calculated by using Darcy’s equation.

The Darcy’s equation for the loss of head due to friction in pipes is as follows:

HL=f*L*V2

D*2g

Where HL=Loss of head due to friction in pipe

f=Friction factor

L=Length of pipe in m

D=Inside diameter of the pipe in m

V=Average velocity of liquid in m/s

G=Acceleration due to gravity in m/s2

Friction losses in Laminar flow

For laminar flow, the friction factor is ‘f’ is function of Reynolds number only and is given by,

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HL= 64*L*V2

Re*D*2g

The above equation is known as the Hagen –poiseuille equation,which is valid only for laminar flow.

Frictional losses in Turbulent Flow

The friction factor ‘f’ for turbulent flow is a function of Reynolds number as well as the relative roughness of the pipe.

The relative roughness is defined as the pipe inside surface roughness(є) divided by the inside diameter of the pipe (D)

10. What is moody diagram?Explain the important characteristics of its.[AU-NOV/DEC-2012]

To determine the value of the friction factor for use in Darcy’s equation,we use the moody diagram.Each curve represents values of friction factor as a function of Reynolds number for a given value of relative roughness.Thus,if we know the Reynolds number and relative roughness.

The following important characteristics should be noted about the moody diagram.

It is plotted on logarithmic paper because of the large range of values encountered for f and NR

At the left end of the chart(Re<2000) the straight line curve gives the relationship for laminar flow:f=64/NR

No curves are drawn in the critical zone (2000< NR<4000),because it is not possible to predict whether the flow is laminar or turbulent in this region.

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For Reynolds numbers greater than 4000,each curve plotted represents a particular value of є/D.For intermediate values of є/D,interpolation is required.

Once complete turbulence is reached(region to the right of the dashed line),increasing values of NR have no effect on the value of f.

11. Explain the Pascal’s law with example.[AU-MAY/JUNE-2012;2014]

Law: Pascal’s law states that the pressure generated at any point in a confined fluid acts equally in all directions.

Bramah’s hydraulic press:

In a hydraulic press ,a small input force is applied to generate a large output force. That is, the hydraulic press amplifies the hydraulic force in the hydraulic systems.

Working

Consider two oil containers both in cylindrical form and connected together contain some oil. Both the cylinders have a piston having different diameters says D1 and D2 respectively, where D1 is smaller than D2 .

If a force F1 is applied to the small-diameter piston, then this will produce an oil pressure P1 at the bottom of the piston1.Now this pressure is transmitted through the oil to the large-diameter piston 2.Because the piston has a larger

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area the pressure at the piston 2 will be P2.Now this pressure P2 will push up the piston to create an output force F2

We know that pascals law,P1=P2

A1=Area of the smaller piston =

A2=Area of the larger piston =

Since A2>A1, therefore F2 will be higher than F1.In otherwords,the hydraulic press amplifies the hydraulic force.

Hydraulic Jack:

To lift the load F2 by a distance s2,the piston P1 must displace specific quantity of liquid by moving by a distance s1

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Volume of oil displaced,V1=s1.A1

V2=s2.A2

Since the displacement volume is identical,V1=V2

s1.A1=s2.A2

The output force is greater than the input force, but the output movement will be lesser than the input movement.

Air-to-Hydraulic pressure booster:

Use:It is a device used for converting compressed air into the higher hydraulic pressure,which is required for operating hydraulic cylinders.Such device can be found in various applications such as booster-powered riveting pressure,and booster-powered clamps on milling machines.

Construction:

Air-to-hydraulic pressure booster arrangement which is commonly employed to clamp workpiece to a machine tool table.

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Working:

If the air piston (having a area A1) is subjected to air pressure P1,then the air will produce a force F1 on the hydraulic cylinder piston.If the area of the hydraulic piston is A2 Such that A2<<A1 then the hydraulic discharge oil pressure will be P2,Now as per Pascal’s law,this oil pressure P2,will be used for clamping a workpiece to a machine tool table.

The pressure ratio of an air to hydraulic pressure can be calculated by using the relation.

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Pressure ratio=

Pressure Transfer:

Pressure P1 produces force F1 on the area A1,Which is transferred through the piston rod to the other end with force F2,acting on area A2 and producing pressure P2.

We know that,P=F/A

F1=P1*A1 and F2=P2*A2 (F1=F2)

12. Write short notes on losses in pipes.[AU-MAY/JUNE-2012]

When liquid flows in a pipe, there will be some energy loss. This loss of energy may be classified as follows.

1.Major energy loss-loss due to friction

2.Minor energy loss

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These losses are due to

1.Losses in valves and pipe fittings

2.Sudden enlargement/contraction of pipe.

3.Bend in pipe.

4.An obstruction in pipe.

13. Describe the various losses in pipe, valves and fittings in hydraulic systems.[AU-APR/MAY-2011]

Losses in pipes:

Losses in pipes are due to the friction i.e. rubbing action between the boundary surface and fluid. This friction builds up the heat and results in energy loss. In addition to this, pressure drop may occur during the flow. In hydraulic systems, pressure drop should be kept as low as possible to obtain high transmission efficiency. This may be done by increasing the design value of diameter of one pipe to some extent. In other words, large diameter pipes reduces the pressure drop across the flow.

Friction may occur due to rubbing of fluid particles and rubbing action between the boundary surface and fluid. This generates excessive heat and results in premature wear of parts.Hence,hydraulic systems are usually designed for laminar flow condition, as losses are minimum in that condition. For this, low velocity should be maintained.

Losses in valves and fittings:

Minor losses occur as the fluid undergoes sudden expansions or contractions or as the fluid flows through the pipe fittings, valves and bends. For many fluid power applications, majority of energy losses are due to change in cross-section of the flow path and the change in flow direction which are usual in these valves,fittings,tees,elbows and bends. Hence the nature of flow through these devices and ancillary components is very complex to predict.However,some experimental techniques are used for determining the losses occurred in such types of flow: Using these techniques, head losses are found to be proportional to the square the velocity of the fluid.

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A constant is introduced to cancel the proportionality nature and the constant is named as K factor or loss coefficient of the valve or fitting. This formula does not hold good under viscous flow.

It is true that the head loss through the minor losses are equal to the loss through some length of straight pipe.

Minor HL=Major HL

In addition to these effects on flow, pressure drop on valves may also affect the flow of fluid. With flow-control valves, manufacturers will provide details of pressure drops at various flow rates in the form of graph. Pressure drop in check valves depends on the control spring in the valve and will vary with the quantity of flow. Pressure drop in direction control valves depends on the flow rate, the spool type, the flow path, the fluid viscosity and temperature.

REVIEW QUESTIONS:

PART-A:

1.Under what conditions pneumatic systems are preferred. [AU-NOV/DEC-2012].

2.Name any four desirable characteristics of hydraulic pumps.[AU-MAY/JUNE-2009]

3. List the primary functions of hydraulic fluid? [AU-NOV/DEC-2012]

4.State Pascal’s law with an industrial example [AU-MAY/JUNE-2012]

5.What is the importance of Reynolds number?(M/J-2014)

6.Draw the symbol of pressure relief valve.(N/D-2013)

7.Give the advantages of fluid power system.(N/D-2013)

8.Give any four important properties of hydraulic fluids. [AU-APR/MAY-2011]

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9.Name the different types of fluid power systems. [AU-APR/MAY-2011]

10.List the applications of fluid power in agriculture and aviation industries. [AU-MAY/JUNE-2013]

11.Give Darcy’s equation to calculate head loss in pipe. [AU-MAY/JUNE-2012;2014]

12.Under what conditions pneumatic systems are preferred. [AU-NOV/DEC-2012]

13.Compare hydraulic and pneumatic drives for automation [AU-MAY/JUNE-2012]

14.Give symbol for shuttle valve DCV and pressure relief valve.[AU-MAY/JUNE-2012]

PART-B:

1. Write short notes on the following; Laminar and Turbulent flow and Darcy-weisbach equation [AU-NOV/DEC-2012]

2.What is moody diagram?Explain the important characteristics of its.[AU-NOV/DEC-2012]

3.Explain the Pascal’s law with example.[AU-MAY/JUNE-2012]

4.Describe the various losses in pipe, valves and fittings in hydraulic systems.[AU-APR/MAY-2011]

5.Explain the advantages of fluid power[APR/MAY-2011;MAY/JUNE-2013;NOV/DEC-2012]

6. How to select oil for the industrial application. [AU-NOV/DEC-2012]

7.Explain the working principle of hydraulic system with neat sketch.[NOV/DEC-2006,2007;M/J-2013;N/D-2013]

8. Explain the working principle of pneumatic system with neat sketch.[NOV/DEC-2006;MAY/JUNE-2013;N/D-2013]

9.List out the properties of hydraulic fluid.[NOV/DEC-2006,2007;MAY/JUNE-2012]

10.Explain the types of hydraulic fluid with advantages and disadvantages.[NOV/DEC-2008;APR/MAY-2008;MAY/JUNE-2012]

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