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UNIT 1 PART B 1.(a) (i) Compare and contrast hydraulic, pneumatic and electromechanical power systems? (ii) write briefly about the following hydraulic fluids? Nov/Dec 2008 (16Marks) 11 a (i,ii) (a) (i) HYDRAULIC,PNEUMATIC AND ELECTROMECHANICAL PREPARED BY | M. KIRAN M.TECH I Electrical/ Electro- Sl.No. Description Hydraulic Pneumatic mechanical 1. Energy Electrical Electrical Electrical used to used to used to drive hydraulic motor of the electric which compressor, the liquid. compresses air/gas. 2. Medium Pressurized Compressed There is no air/gas. used in this rather the transmitted the mechanical components. 3. Energy Accumulator Reservoir Batteries (limited). 4. Regulators Hydraulic Pneumatic Variable drives. 5. Transmitte Transmitted Transmitted Transmitted through through through the cylinders, cylinders, mechanical hydraulic matic components like actuators. and gears, cams, rotary jack, etc. 6. Distributi Limited, Good, can be Excellent, with I local as a plant minimal loss. Up to 100 service. flow rate Upto1000m, = 2-6 m/s. flow rate (v) = 20-40m/s. 7. Operating V=O.5m/s. V = 1.5 m/s. speed ~

APPLIED HYDRAULICS AND PNEUMATICS

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Page 1: APPLIED HYDRAULICS AND PNEUMATICS

UNIT 1 PART B

1.(a) (i) Compare and contrast hydraulic, pneumatic and electromechanical power systems? (ii) write briefly about the following hydraulic fluids?

Nov/Dec 2008 (16Marks) 11 a (i,ii)

(a)(i) HYDRAULIC,PNEUMATIC AND ELECTROMECHANICAL

(ii) HYDRAULIC FLUIDS

Petroleum base hydraulic fluidsHydraulic were among the first liquids employed as hydraulic or power transmission fluids. The typical

petroleum oils include: Naphthenic, aromatics, paraffin’s, wax and olefins.Emulsions

Emulsions are water oil mixtures. The emulsions are available in two gene real types: oil in water emulsions or water in oil emulsions.

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I Electrical/ Electro-

Sl.No. Description Hydraulic System

Pneumatic System mechanical System1. Energy Electrical energy

is 0 Electrical energy is

Electrical energy is used to drive the used to drive the used to drive the hydraulic pumps, motor of the electric motors. which compressor, which the liquid. compresses the

air/gas.

2. Medium Pressurized liquid.

Compressed There is no medium air/gas. used in this system,

rather the energy is transmitted through the mechanical components.

3. Energy storage Accumulator Reservoir (good). Batteries (limited). (limited).

4. Regulators Hydraulic valves.

Pneumatic valves. Variable frequency drives.

5. Transmitters Transmitted Transmitted Transmitted through hydraulic

through pneumatic through the cylinders, and cylinders, pneu- mechanical hydraulic rotary matic rotary components like actuators. and pneumatic gears, cams, screw-

rotary actuators. jack, etc. 6. Distribution Limited,

basically a Good, can be treated

Excellent, with I system local facility. as a plant wide minimal loss.

Up to 100 m, service. flow rate (v) Upto1000m, = 2-6 m/s. flow rate (v)

= 20-40m/s. 7. Operating V=O.5m/s. V = 1.5 m/s.

speed ~

Page 2: APPLIED HYDRAULICS AND PNEUMATICS

The oil in water emulsion has water as the continuous base and the oil is present in lesser amounts as the dispersed media. In the water in oil emulsion the oil is in continuous phase and the water is the dispersed media.

Glycols

Glycols are often referred by several names such as polyglycols, polyalkylene glycols, and polyether’s. these glycols are extensively used as base stocks and as components for synthetic lubricants and hydraulic fluids, air conditioner lubricants, and heavy duty brake fluids.

2. (b)(i) List all properties that a good hydraulic fluid should possess? (ii) Fluid is flowing through a tapering pipe having diameters 50mm and 25mm at sections 1 and 2 respc. The discharge through the pipe is 7.5 Lps. The section 1 is 3m above datum and section 2 is 1.25m above datum. If the pressure at section 1 is 200 kpa, find the pressure at section 2. The specific gravity of the fluid is 0.9.

Nov/Dec 2008 (16Marks) 11 b (i,ii)(b)(i) PROPERTIES OF HYDRAULIC FLUID

(ii) Given data:Diameter,D1=50mm:Diameter D2=25mmQ=7.5 LPSDatumn at 1, Z1=3mDatumn at 2, Z2=1.25mPressure, P1=200KPa

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Page 3: APPLIED HYDRAULICS AND PNEUMATICS

specific gravity=0.9Solution.

A1=π4

x(50x10-3)2= 1.963x10^-3 m2

A2=π4

x(25x10^-3)2=4.91x10^-4 m2

Specific gravity = W fluid/W waterWeight density of fluid, w=0.9x9810=8829N/m3Q=A1V1=A2V2 V1=Q/A1=( 7.5X10^-3)/1.963X10^-3=3.82m/sV2=Q/A2=(7.5X10^-3)/4.91X10^-4=15.28m/sNow applying Bernoulli’s equation

Z1+¿/2g) + (p1/w) = Z2+¿/2g) + (p2/w)

3 + (3.8 12/2 x 9.81) + ( 200 x10^3/8829) = 1.25 + (15. 282/2 x 9.81)+ (P2/8829)

Ans. Pressure at section 2, P2= 116.95 kPa

3. (a)(i) Describe any four advantages of fluid power systems? (ii) Differentiate between laminar and turbulent flow with examples?

May/June 2009 (16 Marks) 11 a(i,ii)(a)(i) FOUR ADVANTAGES OF FLUID POWER SYSEMS

Multiplication of force:The fluid power system can multiply forces easily and efficiently. Constant force: The fluid power system is the only system which can provide constant force or torquw irrespective of

variations in speed, whether the work output moves a few millimeters per minute, several meters per minute. Simplicity, safety, economy: When compared to electrical and mechanical systems, generally the fluid power system uses few moving

parts. That’s why they are simpler to maintain and operate. As a result, it also maximizes safety, compactness, and reliability.

Other benefits: Some of the other advantages of using the fluid power systems include: High power to weight ratio, instant

reversal of motion with accuracy is possible, automatic protection against over loads, requires lesser space, Relatively smooth and quiet operation.

Power transmissionIt requires less mechanical parts. The problem of breakage of parts like gears, cams, belts and chains is not

involved. Lesser noise Less noise and less vibration can be ensured from the system by proper installation of fluid system. Forces

can be conveyed up and down with less loss in efficiency System overloading can be prevented by use of automatic relief valves Economical compared to other modes.

(ii) LAMINAR FLOW AND TURBULENT FLOW WITH EXAMPLESa. 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 flaw is characterized' by the fluid flowing in' smooth I layers, of laminae.

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Page 4: APPLIED HYDRAULICS AND PNEUMATICS

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(i) Flow of oils in measuring instruments. (ii) Flow of blood in veins and arteries. (iii) Rise of water in plants through their roots.

b. Turbulent Flow A turbulent flow is that flow in which fluid particles move in a zigzag way. The turbulent flow' is characterized by continuous small fluctuations in the magnitude and direction of the velocity of the fluid particles The turbulence in the fluid may cause (i) More resistance to flow (ii) Greater energy loss, and (iii) 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.

4.(b) (i) Describe any four applications of fluid power systems? (ii) Draw a schematic layout of hydraulic power pack with symbols?

May/June 2009 (16 Marks) 11 b(i,ii)(b)(i) FOUR APPLICATIONS OF FLUID POWER SYSTEMSAutomotive: Power, brakes, power steering power windows and powered seat adjustments are all typical fluid power devices. At the production lines, fluid power is used to operate the presses' that from body parts and fender to punch holes, and heads of rivets which hold the frame together, to actuate heads, slides, and chucks of the machinery that is used to produce engine parts, to spin the wheels which, polish ,the finishes, and to index "the line" itself Aviation: The pilot lifts his landing' gear and 'controls ailerons, rudders, elevators and trim tabs with fluid power. In the fighter aircrafts, fluid power opens the bomb bays and rotates the turrets., Wing and fuselage sections are formed in stretch presses that are operated by fluid power. Construction: Fluid power is used to break rocks, and dig into the earth for the construction of tunnels, dams, roads or seaways. Fluid power is used on road graders, shovels, crushers and rock drills. Rollers, scrapers, bulldozers, vibrator screens, draglines truck loaders, and asphalt mixers all use 'fluid power. Even the smaller tools that are used in construction for heading of rivets, breaking of concrete or jack hammer etc depend on fluid power. . Chemicals: Remote control of valves, big and small, used throughout the chemical process industries comprises one of the more important newer applications of fluid power. It controls hopper gates and operates discharge doors of mixers and treating chambers. Fluid power regulates roll pressures in blending mills, packs chemicals into containers, and actuates panel controls. Defense: Fluid power aims antiaircraft batteries, rotates tank turrets, catapults aircraft from flight decks, and elevates guided missiles to reach -targets, Ownerships, fluid power is used for steering, hoisting, positioning, and opening and closing operations.

(ii) SCHEMATIC LAYOUT OF HYDRAULIC POWER PACK

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Page 5: APPLIED HYDRAULICS AND PNEUMATICS

Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a fluid for transmitting energy from an energy-generating source to an energy-using point to accomplish useful work. Figure .Shows a simple circuit of a hydraulic system with basic components.Functions of the components .

The hydraulic actuator is a device used to convert the fluid power into mechanical power to do useful work. The actuator may be of the linear type (e.g., hydraulic cylinder) or rotary type(e.g., hydraulic motor) to provide linear or rotary motion, respectively.

The hydraulic pump is used to force the fluid from the reservoir to rest of the hydraulic circuit by converting mechanical energy into hydraulic energy.

Valves are used to control the direction, pressure and flow rate of a fluid flowing through the circuit.

The piping shown in Fig. is of closed-loop type with fluid transferred from the storage tank to one side of the piston and returned back from the other side of the piston to the tank. Fluid is drawn from the tank by a pump that produces fluid flow at the required level of pressure. If the fluid pressure exceeds the required level, then the excess fluid returns back to the reservoir and remains there until the pressure acquires the required level. Cylinder movement is controlled by a three-position change over a control valve. 1. When the piston of the valve is changed to upper position, the pipe pressure line is connected to port A and thus the load is raised. 2. When the position of the valve is changed to lower position, the pipe pressure line is connected to port B and thus the load is lowered. 3. When the valve is at center position, it locks the fluid into the cylinder (thereby holding it in position) and dead-ends the fluid line (causing all the pump output fluid to return to tank via the pressure relief).

In industry, a machine designer conveys the design of hydraulic systems using a circuit diagram the components of the hydraulic system using symbols. The working fluid, which is the hydraulic oil, is stored in a reservoir. When the electric motor is switched ON, it runs a positive displacement pump that draws hydraulic oil through a filter and delivers at high pressure. The pressurized oil passes through the regulating valve and does work on actuator. Oil from the other end of the actuator goes back to the tank via return line. To and fro motion of the cylinder is controlled using directional control valve.

5.(a)(i) List out the advantages and disadvantages of hydraulic power system? (ii) What are the functions of a fluid in any fluid power systems? (iii) What are the required properties of a good hydraulic fluid?

April/May 2008 (16Marks) 11 a (i,ii,iii)(a)(i) ADVANTAGES OF HYDRAULIC POWER SYSTEM

Refer question NO. 3 a(i)

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Page 6: APPLIED HYDRAULICS AND PNEUMATICS

Disadvantages: Hydraulic fluid is highly corrosive to most of the aircraft materials.  Due to the heavy loads experienced in a typical hydraulic system, structural integrity is a must which

also means higher structural weight for the aircraft in addition to the weight of its hydraulic lines, pumps, reservoirs, filters, & etc. 

Hydraulic system is susceptible to contaminations & foreign object damage (FOD).  Mishandling and constant exposure to hydraulic fluid and its gas fumes without proper equipment and

precautions is a health risk.  If disposed improperly, a hydraulic fluid is an environmental risk.

(ii) FUNCTIONS OF FLUID POWER SYSTEMS To Transmit Power To Lubricate Moving Parts To seal gaps and clearances between mating components To dissipate heat generated by internal friction To prevent rust and corrosion To remove unwanted and harmful impurities from the system

(iii) PROPERTIES OF GOOD HYDRAULIC FLUID

Refer question No. 2 b (i)6.(b) Write short notes on the following

i. Laminar and turbulent flowii. energy losses in valves and fittingsiii. darcy’s Equation

April/May (2010) ( 16Marks) 11 b (i,ii,iii)(i) LAMINAR AND TURBULENT FLOW

Refer question No. 3 (a)(ii)

(ii) ENERGY LOSSES IN VALVES AND FITTINGSWhen liquid flows in a pipe, there will be some energy loss. This loss of energy may be classified as

follows:1. Major energy losses

This loss is due to friction2. Minor energy losses

These losses are due to:i. Losses in vales and pipe fittingsii. Sudden enlargement of pipe,iii. Bend in pipeiv. An obstruction in pipe.

(iii) DARCY’S EQUATIONThe major energy losses due to friction in the pipe can be calculated by using Darcy’s Equation.The Darcy Equation is a theoretical equation that predicts the frictional energy loss in a pipe based on the

velocity of the fluid and the resistance due to friction. It is used almost exclusively to calculate head loss due to friction in turbulent flow.

 Where:

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Page 7: APPLIED HYDRAULICS AND PNEUMATICS

hf = Friction head lossf = Darcy resistance factorL = Length of the pipeD = Pipe diameterV = Mean velocityg = acceleration due to gravity

The Darcy friction factor, f, is usually selected from a chart known as the Moody diagram. The Moody diagram is a family of curves that relate the friction factor, f, to Reynolds number, Re, and the relative roughness of a pipe, e/D.

7. (a)(i) Compare and contrast hydraulic, pneumatic and electromechanical power systems? (ii) List out the application of fluid power employed in different industries?

Nov/Dec 2010 (16Marks)11 a(i,ii)(a)(i) HYDRAULIC,PNEUMATIC AND ELECTROMECHAL POWER SYSTEMS

Refer question No. 1 a (i)(ii) APPLICATIONS OF FLUID POWER SYSTEMS

Refer Question No. 4 b (i)8. (b) (i) Fluid is flowing through a tapering pipe having diameters 50mm and 25mm at sections 1 and 2 respc. The discharge through the pipe is 7.5 Lps. The section 1 is 3m above datum and section 2 is 1.25m above datum. If the pressure at section 1 is 200 kpa, find the pressure at section 2. The specific gravity of the fluid is 0.9. (ii) Write Pascal’s law. Explain any one applications of Pascal’s law with neat diagram?

Nov/Dec 2010 16 Marks 11 b(i,ii)(b) (i) PROBLEM

Refer Question No. 2 b(ii) (ii) PASCAL’S LAW

Pascal's law or the principle of transmission of fluid-pressure is a principle in fluid mechanics that states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations (initial differences) remain the same.

Example: Hydraulic pressThe hydraulic press depends on Pascal's principle: the pressure throughout, a closed system is constant. One part

of the system is a piston acting as a pump, with a mod mechanical force, acting on a small cross-sectional area the other part is' a piston with a larger area which generate correspondingly large mechanical, force. Only small-diameter tubing (which more easily resists pressure is needed if pump is separated from the press cylinder.

The hydraulic press is a type of machine based u Pascal's principle, that is when a fluid completely fills a vessel and a pressure is applied to it at any part 'of its surface, that pressure is transmitted equally throughout the whole of enclosed fluid. The hydraulic press has numerous uses, the compression of soft materials such as waste paper and cotton into compact pales to the shaping of motor-car 'bodies and the forging of steel armor plate. In its simplest form the hydraulic press consists of a cylinder and piston of large diameter, connected by a pipe to' a force pump of much smaller diameter. Oil from a supply tank is pumped into the cylinder and the piston (or ram) moves out, exerting, considerable force. A valve is provided to release the pressure and allow the oil to return to the tank, after the press has done its' work.

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Page 8: APPLIED HYDRAULICS AND PNEUMATICS

9. (a) (i) what are the basic component that are required for a hydraulic system? Explain their functions? (ii) What types of fluid are available for hydraulic system? Explain two of them?

Nov/dec 2011 (16 Marks) 11 a (i,ii)(a)(i) BASIC COMPONENTS FOR HYDRAULIC SYSTEMActuators: Hydraulic actuators are the end result of Pascal's law. This is where the hydraulic energy is converted back to Mechanical energy. This can be done through use of a hydraulic cylinder which converts hydraulic energy into linear motion and work, or a, hydraulic motor which converts hydraulic energy, into 'rotary motion and work. As with, "hydraulic pumps, hydraulic cylinders and hydraulic motors' have several different subtypes, each intended for specific design applications.Reservoir: The purpose of the hydraulic reservoir is to hold a volume of fluid, transfer hear from the system, allow solid contaminants to settle and facilitate the release of air and moisture from the fluid.Pump: The hydraulic pump transmits mechanical energy in to hydraulic energy. This is done by the movement of fluid which is the transmission medium. There are several type of hydraulic pumps including gear, vane and piston. All of these pumps have different subtypes intended for specific applications such as a bent axis piston pump or a variable displacement vane pump. All hydraulic pumps work on the same principle, which is to displace fluid volume against a resistant load or pressure.Valves: hydraulic valves are used in a system to start, stop and direct fluid flow. Hydraulic valves are made up of poppet’s or spools and can be actuated by means of pneumatic, hydraulic, electrical, manual or mechanical means.

FiltersFilters are used to remove any foreign particles so as keep the fluid system clean and efficient, as well as

avoid damage to the actuator and valves. Pressure regulator regulates (i.e., maintains) the required level of pressure in the hydraulic fluid.

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Page 9: APPLIED HYDRAULICS AND PNEUMATICS

(ii) TYPES OF FLUID FOR HYDRAULIC SYSTEM

Refer question No. 1 a(ii)

10. (b) (i) Write short notes on 1. Laminar and turbulent flow 2. Reynolds number?(ii) Explain the working principle of hydraulic press with neat sketch?

Nov/Dec 2011 (16Marks) 11 b (i,ii)(b)(i) LAMINAR AND TURBULENT FLOW

Refer question No. 3 (a)(ii)

(ii) HYDRAULIC PRESSRefer Question No. 8 (b) (ii)

11. a(I) What are the essential and desirable properties of a hydraulic fluid? Discuss? (ii) list the precautions to be taken when a mineral oil based fluid is changed into fire resistant fluid.?

April/May 2010 16 Marks 11 a(I,ii)(i) Refer Question Number 2b(i)

(ii) MINERAL OIL BASED FLUID

Key check points for any conversion of mineral oil based fluid in to fire resistant fluid are as follows: Compatibility of each of the components in the circuit with the fire resistant fluid to be introduced in

to the circuit as a replacement (seals, packing’s, hoses and coatings) Draining and cleaning ( pipes, valves, tanks, strainers, filters, and cartridges, pumps, etc.,) Flushing Refilling and checking, including specific system and oil monitoring.

12. b (I) explain how Bernoulli’s equation can be used to determine the pressure drop between two statins in a hydraulic system. Assume that there is some number of bends, tees, elbows, and globe and gate valves in between these two stations separated by a long distance. (ii) Oil with specific gravity 0.9 enters a tee, as shown in fig.5, with velocity v1=5m/s. the diameter at section 1 is 10cm, the diameter at section 2 is 7 cm and the diameter at 3 is 6 cm. if equal flow rates are to occur at section’s 2 and 3, find v2 and v3 is m/s

April/May 2010 16 Marks 11 b(i,ii)(i) BERNOULLI’S EQUATION

In an ideal, incompressible fluid when the flow is steady and continuous, the sum of potential energy, kinetic energy and pressure energy is constant across all cross section’s of the pipeFor the incompressible fluid flowing through a non uniform pipe shown in fig.

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Page 10: APPLIED HYDRAULICS AND PNEUMATICS

ENERGY EQUATIONBernoulli’s Equation stated earlier was based on the assumption that fluid is ideal and therefore friction

less. But practically all fluids are real and therefore there are always some losses during the fluid flow. These energy losses have to be taken into consideration in the application of bernoulli’s equation which gets modified for real fluids as follows:

And also refer question No. 6 b (i,ii,iii)

13. a compare the use of fluid power to a mechanical system by listing advantages and disadvantages?April/ May 2011 16 marks 11 (a)

(a) Refer question No 3 a(i) Disadvantages

Hydraulic fluid is highly corrosive to most of the aircraft materials.  Due to the heavy loads experienced in a typical hydraulic system, structural integrity is a must which

also means higher structural weight for the aircraft in addition to the weight of its hydraulic lines, pumps, reservoirs, filters, & etc. 

Hydraulic system is susceptible to contaminations & foreign object damage (FOD).  Mishandling and constant exposure to hydraulic fluid and its gas fumes without proper equipment and

precautions is a health risk.  If disposed improperly, a hydraulic fluid is an environmental risk.

14.b List and explain various hydraulics fluids?April/May 2011 16 Marks 11 (b)

Refer Question No. 1 a(ii) 2 b (i) |

Page 11: APPLIED HYDRAULICS AND PNEUMATICS

15.a) (i) Explain in detail any eight desirable properties of a good hydraulic fluid? (ii) Explain the advantages and limitation’s of using petroleum based hydraulic oils?

May/June 2012 16 marks 11 a(I,ii)(i) Refer Question NO. 2 b (i)

(ii) ADVANTAGES AND LIMITATIONS OF USING PETROLEUM BASED HYDRAULIC OILS Good lubricating characteristics Protection against rust, corrosion, sludge and foam formation Longer life Better heat dissipating capability Better sealing property Generally these oils have a high viscosity index so that they may be used over a wide

temperature range.LIMITATIONS

Low fire resistance Tendency to oxidize rapidly

16. b) (i) Hydraulic oil of kinematic viscosity 0.9 strokes, flows through a 35mm diameter pipe at a velocity of 4m/s for a length of 100m. find the head loss due to friction. Assume specific gravity of oil as 0.90. (ii) State the significance of K-factor in determining the losses in valves and fittings. Determine the head loss across a 40mm wide open gate valve, when hydraulic oil of specific gravity 0.9 flows through it at rate of 0.015m3/s. the k-factor for wide open gate valve is 0.19.

May/June 2012 16 Marks 11 b (i,ii)(i)

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