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10/21/2015Hydraulic and Pneumatic Systems2Hydraulic SystemsChapter-3 Week 5

2Chapter-1PneumaticHydraulicCompressed Air Industrial OilLight loads,6-8 barsHeavy loads, unlimited, no OLFast, erraticSlow, stableCompressorPumpCompressible IncompressibleAir Receiver/Air ReservoirTankExhaust to AtmosphereLiquid back to TankPU tubesHi pressure Wire braided hoseHydraulics is the study of fluid forces whether at rest or in motion. Two branches : Hydrostatic and Hydrodynamics.Fluid flow10/21/2015Hydraulic and Pneumatic Systems4Flow is a loose term that generally has three distinct meanings:volumetric flow is used to measure volume of fluid passing a point per unit of time. Where the fluid is a compressible gas, temperature and pressure must be specified or flow normalised to some standard temperature and pressuremass flow measures the mass of fluid passing the point in unit timevelocity of flow measures linear speed (in m s -1, say) past the point of measurement. Flow velocity is of prime importance in the design of hydraulic and pneumatic systems.4Laminar and turbulent flow10/21/2015Hydraulic and Pneumatic Systems5

The nature of the flow is determined by the Reynolds number, R c, given by the expression:

5Flow through pipes10/21/2015Hydraulic and Pneumatic Systems6

Volume flow rate is Q=vAMass flow rate is Qm=vAWhere v is average velocity6Where v is average velocityPressure and Force.10/21/2015Hydraulic and Pneumatic Systems7Pressure is force exerted against a specific area (force per unit area)An example of pressure is the air (gas) that fills an automobile tire.Force is anything that tends to produce or modify (push or pull) motion and is expressed in Newton. F = PAPressure =Force/Area; N/m2Power=Work/time=Nm/sWork =Force X distance travelled=NmFlow rate= Area x velocity; Q=AV=m2.m/sPower= Pressure x Flow Rate=N/m2x m3/s=J/s=WTorque= Force x radius=NmBasic Formula

Units of PressurePascal's Law.10/21/2015Hydraulic and Pneumatic Systems11Blaise Pascal formulated the basic law of hydraulics in the mid 17th century.He discovered that pressure exerted on a fluid acts equally in all directions. His law states that pressure in a confined fluid is transmitted undiminished in every direction and acts with equal force on equal areas and at right angles to a container's walls.It is known for Equilibrium and force amplification as long as the distance or lever arm is enough ( from the small diameter pipe /tube but with long lever arm) to equate the WORK from bigger diameter but small distance on the other side of the system.Basic Physical Laws

10/21/2015Hydraulic and Pneumatic Systems12Pressure EquilibriumForce -Area-Distance Area relationshipWork =Fd1lb x 10 in=10lbs x inchPressure Equilibrium1 lb/1 sq in.=10 lbs/10 sq in.Pascals Law=Force multiplication with constant pressure

P=37500 kgf/15,000 cm2=2.5kg/cm2250 kg/ 100 cm2=2.5 kg/cm2P=5kg/2 cm2=2.5 kg/cm2F=2.50 kgf x 15000 cm2=37,500 kgfPressure is uniform=2.5kgf/cm2Pascals LawPf = P0 + ghWhen there is an increase in pressure at any point in a confined fluid, there is an equal increase at every point in the container.In a fluid, all points at the same depth must be at the same pressure.Consider a fluid in equilibrium.

PA - Ahg P0A = 0P = P0 + ghHydraulicsPressure is equal at the bottom of both containers (because its the same depth!)P = F2/A2 = F1/A1 and since A1 < A2, F2 > F1 There is a magnification of force, just like a lever, but work stays the same! (conservation of energy). W = F1* D1 = F2 * D2 D1 > D2

You have to push down the piston on the left far down to achieve some change in the height of the piston on the right.Bernoullis Equation(Continuity Equation)Bernoullis equation is an equation used to determine the head of the fluid.Energy Entering the system = energy Leaving the system + EnergyLossEf=flow energy of mass entering the systemP =potential energyK= kinetic energy of mass entering the system10/21/2015Hydraulic and Pneumatic Systems16Law of conservation of mass/EnergyEf1 + P1+K1=Ef2 + P2 + K2Bernoullis equation for an Ideal systemNeglecting friction, the total head or the total amount of energy per unit mass or weight is the same at every point in the path of flowWith continuous steady flow, the total head at any point in the stream is equal to the total head at any downstream point plus the head loss between two points..10/21/2015Hydraulic and Pneumatic Systems17Bernoullis equation if friction is consideredDerivation of Bernoullis Equation

Consider the change in total energy of the fluid as it moves from the inlet to the outlet. Etotal = Wdone on fluid - Wdone by fluid Etotal = (1/2mv22 + mgh1) (1/2mv12 + mgh2)Wdone on fluid - Wdone by fluid = (1/2mv22 + mgh1) (1/2mv12 + mgh2)P2V2 - P1V1 = (1/2mv22 + mgh1) (1/2mv12 + mgh2) P2 P1 = (1/2 v12 + gh1) (1/2 v12 + gh1)

Etotal = 1/2mv2 + mgh W = F/A*A*d = PVP2 + 1/2 v12 + gh1 = P1 + 1/2 v12 + gh1 Venturi TubeA2 < A1 ; V2 > V1According to Bernoullis Law, pressure at A2 is lower.Choked flow: Because pressure cannot be negative, total flow rate will be limited. This is useful in controlling fluid velocity.

P2 + 1/2 v12 = P1 + 1/2 v12 ; P = /2*(v22 v12)Daniel BernoulliA Swiss scientist born in 1700s that is most famous for his work in fluid pressure. He died in 1782.

BERNOULLIS THEOREMBernoullis theorem which is also known as Bernoullis principle, states that an increase in the speed of moving air or a flowing fluid is accompanied by a decrease in the air or fluidspressure or sum of the kinetic (velocity head), pressure(static head) and Potential energy energy of the fluid at any point remains constant, provided that the flow is steady, irrotational, and frictionless and the fluid is incompressible.

BERNOULLIS EQUATION

If a section of pipe is as shown above, then Bernoullis Equation can be written as;22BERNOULLIS EQUATIONWhere (in SI units)

P= static pressure of fluid at the cross section;= density of the flowing fluid in;g= acceleration due to gravity;v= mean velocity of fluid flow at the cross section in;h= elevation head of the center of the cross section with respect to a datum.

HOW TO VERIFY?The converging-diverging nozzle apparatus (Venturi meter) is used toshow the validity of Bernoullis Equation. The data taken will show the presence of fluid energy losses, often attributed to friction and the turbulence and eddy currents associated with a separation of flow from the conduit walls.

APPARATUSES USEDArrangement of Venturi meter apparatus(fig.1)Hydraulic bench(fig. 2). Stop watch(fig.3).

fig. 2fig. 3PROCEDURENote down the inlet, throat and outlet section areas.Measure the distances of inlet, throat ant outlet section from origin.Switch on the motor attached to hydraulic bench.If there any water bubble is present in tube remove it by using air bleed screw. Fully open the control valve.Note down the reading of piezometer corresponding to the section, simultaneously note down the time required to a constant rise of water in volumetric tank(say of 10).Varying the discharge and take at least six readings.

OBSERVATIONSVolume = 1000 cm3Distance of inlet section from origin= 5.5 cmDistance of throat section from origin= 8.1 cmDistance of outlet section from origin= 15.6 cmArea of inlet section= 4.22 cm2Area of throat section= 2.01 cm2Area of outlet section= 4.34 cm2

OBSERVATIONSS NO.TIME(sec)PIEZOMETRIC HEAD(cm)INLETSECTIONTHROATSECTIONOUTLETSECTION190.4019.817.519.3292.9019.917.319.23101.2619.417.418.84106.0019.417.418.85110.0019.617.619.06115.6519.217.618.8CALCULATED VALUESQ(cm3/s)VELOCITY(v) (cm/sec)VELOCITY HEAD (cm)TOTAL ENERGY HEAD (cm)LOSS OF ENERGY(cm)v1v2v3v12/2gv22/2gv32/2gE1E2E3E1-E2E1-E3110.6226.255.025.40.351.540.3120.119.019.61.100.51107.6425.553.524.80.331.460.3120.218.719.51.470.7198.7623.449.122.70.271.230.2619.618.619.01.040.6194.3422.346.921.70.251.120.2419.618.519.01.130.6190.9121.545.220.90.231.040.2219.818.619.21.190.6186.4720.443.019.90.210.940.2019.418.519.00.870.41RESULTSIt is observed from the calculated value that at section where area is less velocity is high and pressure is low which validates the Bernoullis Equation. Graphs are plotted between distance v/s piezometric head and distance v/s total energy but from the graph (B) we can observe that there is dissipation in energy at last point this is because to achieve an ideal condition practically is not possible. APPLICATIONS The Bernoullis equation forms the basis for solving a wide variety of fluid flow problems such as jets issuing from an orifice, jet trajectory flow under a gate and over a weir, flow metering by obstruction meters, flow around submerged objects, flows associated with pumps and turbines etc.Apart from this Bernoullis equation is very useful in demonstration of various aerodynamic properties like Drag and Lift.APPLICATIONSDRAG AND LIFT

Fast Moving Air; Low Air PressureAir travels farther Slow Moving Air; High Air PressureairfoilLeading edgeTrailing edgeAPPLICATIONS

SummaryBernoullis equation is valid for flow as it obeys the equation.As the area decreases at a section (throat section) velocity increases, and the pressure decreases.

Velocity becomes high but the pressure drops a the throat.Hydraulic PowerSystems

Power SystemSymbol for Pumps

PumpsHydraulic pumps convert mechanical energy from a prime mover (engine or electric motor) into hydraulic (pressure) energy. The pressure energy is used then to operate an actuator.Pumps push on a hydraulic fluid and create flow.PUMPHydraulic pump is heart of a hydraulic system. It pumps oil in hydraulic system and converts the mechanical energy of prime-mover into hydraulic energy. (Hydraulic horsepower). Only positive displacement types of pumps are used in high-pressure hydraulic system.Description of a PumpTypeDisplacementDeliveryPressure RatingVolumetric Efficiency

Terms related to pumps: -

A pump is described in following terms.a) Type of Pump: -There are three types of pumps namely, vane pump, gear pump and piston pump. These each type of pumps has many verities, which will be discussed later in this chapter.b) Displacement: -This is oil discharge of pump per revolution of its shaft. This is generally indicated as Cubic Centimeter per revolution.c) Delivery: -This is total discharge of pump at particular RPM of prime mover, and at particular pressure. It is indicated as liters per minute. Delivery of pump changes with RPM of primemover and operating pressure, hence it is generally indicated as graph. For example a vane pump of 28 CC per revolution displacement will have 40 LPM discharge at 1440 RPM at 10 kg/cm2 working pressure, and same pump will have 35 LPM discharge at 1440 RPM and 175 kg/cm2 working pressure.

d) Pressure Rating: -Vane pump can operate up to maximum pressure 210 kg/cm2, Gear pump 250 kg/cm2, and Piston pump 550kg/cm2. This is the maximum limit; many manufacturers have much less working pressure. Hence it is indicated with pump, so that it is always operated within safe limit, to avoid any damage to pump.

e) Volumetric Efficiency: - All pump give higher or theoretical discharge at low-pressure. And discharge decrease as pressure increase due to internal leakage between various parts of pump.Efficiency = Actual Output / Theoretical Output.Higher the efficiency, better the performance and low heat generation and rise in temperature of oil.

VaneGearPiston 210 bars250 bars550 barsGear Pumps

Applications:Forklift, Hydraulic mobile crane, tractor etc. uses gear pump.Maximum Pressure : 250 barsExternal Gear Pump

Internal Gear Pump

Vane Pumps

. Vane pumps are economical and simple in maintenance and repair. Their discharge capacity can be changed by simply changing cam ring, vanes, pressure-plate etc. all are made from harden alloy steel, hence they are comparatively less susceptible to heat and oil contamination as compare to other pump. Hence for most moderate pressure and heavy duty operation vane pumps are most suited. Most of the injection mounding machines uses vane pump.Application: Injection moulding Machine hydraulic pump Vane PumpsMaximum pressure : 210 barsFluid flow from vane-type double pumps

Piston PumpsMaximum pressure : 550 bars barsNon-positive-Displacement PumpsWith this pump, the volume of liquid delivered for each cycle depends on the resistance offered to flow. A pump produces a force on the liquid that is constant for each particular speed of the pump. Resistance in a discharge line produces a force in the opposite direction. When these forces are equal, a liquid is in a state of equilibrium and does not flow.General Types of PumpNon positive displacement Valve

Positive displacement pump With this pump, a definite volume of liquid is delivered for each cycle of pump operation, regardless of resistance, as long as the capacity of the power unit driving a pump is not exceeded.If an outlet is completely closed, either the unit driving a pump will stall or something will break. Therefore, a positive-displacement-type pump requires a pressure regulator or pressure-relief valve in the systemPositive displacement pumps

Positive displacement pumps

PerformancePumps are usually rated according to their volumetric output and pressure.Volumetric output (delivery rate or capacity) is the amount of liquid that a pump can deliver at its outlet port per unit of time at a given drive speed, usually expressed in GPM or cubic inches per minute.ContndPressure is the force per unit area of a liquid, usually expressed in psi. (Most of the pressure in the hydraulic systems covered in this manual is created by resistance to flow.Resistance is usually caused by a restriction or obstruction in a path or flowPressure is the force per unit area of a liquid, usually expressed in psi. (Most of the pressure in the hydraulic systems covered in this manual is created by resistance to flow.Resistance is usually caused by a restriction or obstruction in a path or flowContdAs pressure increases, volumetric output decreases. This drop in output is caused by an increase in internal leakage (slippage) from a pump's outlet side to its inlet sideSlippage is a measure of a pumps efficiency and usually is expressed in percent.Displacement is the amount of liquid transferred from a pumps inlet to its outlet in one revolution or cycle.In a rotary pump, displacement is expressed in cubic inches per revolution and in a reciprocating pump in cubic inches per cycle.Fluid flow from vane-type double pumps

Electric MotorsMotor

PRIME-MOVER (MOTOR)Two types of prime movers are used in hydraulic system. Electric Motor I. C. EngineThe hydraulic system used in mobile vehicles drives their power from main I. C. Engine of automobile. As well as those hydraulic equipments, which are going to be used at those areas where there is no electricity supply, then in such case also I.C. engine are used to drive the hydraulic pump of hydraulic equipment.

Electric motors are convenient and most commonly used prime-mover in hydraulic system.

Electric Motors :-1. Standard motors are available in four speeds 750, 1000, 1440, 3000 RPM. In hydraulicgenerally 1440 RPM is used.

2. Standard motors are available in many classes of insulation. In hydraulic power pack weuse F class of insulation. Common motor have B class insulation, good quality motorE grade insulation but F grade is best, most reputed manufacturer using F gradeinsulation.

3. In refinery and chemical plant, a small spark in junction box, connection box of motormay cause an explosion or fire. Due to the combustible fumes around. Hence in suchatmosphere Flame and Explosion Proof electrical items are used. Such items havetwo metallic casing or enclosure. In one casing main equipment is enclosed and in otherenclosure its electrical connection is fitted. All incoming and outgoing wires are throughspecial cables and gland. All these arrangement is done so the heated surface and sparkdo not come in contact with outside combustible atmosphere. And due to residualcombustible gases even if an explosion take place within enclosure of electrical componentthen it remain confined in enclosure and do not come-out in open atmosphere.Electric motor, solenoid valves, limit switch etc. are available in flame and explosionproof grade. Hence whenever such requirement of safety arises, only such safe electrical item should be used.

4. Motors are made in many grade of protection against entry of water and dust etc. generallycommercial grade of motor are with protection grade of IP44. But better grade protectionis IP65 in which case water can not enter in motor from rear (Fan side)?

5. Nowadays most of the pumps are flange mounted type. If such pumps are coupled toflange of motor through a accurately machined bracket and coupling, then centerline ofpump and motor can be accurately controlled. Which increases bearing life of both motorand pump? Hence always try to select flange type motor. In market vertical flange mountedmotor, and horizontal foot mounted motor with flange is available. According torequirement they should be selected.

At full load and working pressure electric motor should draw only 90% of it full rated current.

7. When a hydraulic system starts and motor is switch on, motor may start with no load on it, or full load on it. In case of no load start equipment, use slip ring type of electric motor, and in full load start type of requirement use squire cage type of electric motor.

8. Up to 15HP and no load start type of requirement DOL starter could be used while above 15HP use star-delta type of motor-starter.

Hydraulic Power Pack/TankTank/Power Pack Unit

TankThe reservoir systemThe 'reservoir' as the name suggests, is a tank which provides uninterrupted supply of fluid to the system, by storing the required quantity of fluid. The hydraulic fluid is considered the most important component in a hydraulic system or in other words its very heart. Since the reservoir holds the hydraulic fluid, its design is considered quite critical.The reservoir functions such as dissipating heat through its walls, conditioning of the fluid by helping settle the contaminants, aiding in the escape of air and providing mounting support for the pump and various other components.. Some of the essential features of any good reservoir include components such as: Baffle plate for preventing the return fluid from entering the pump inlet Inspection cover for maintenance accessFilter breather for air exchange Protected filler opening Level indicator for monitoring the fluid level Connections for suction, discharge and drain lines.The monitoring of the temperature of the fluid in the reservoir is also important. At the very least, a simple visual thermometer whose ideal temperature range is around 45 C (113 ^^F) to 50 C (122 F), needs to be provided on the reservoir.

.Filter Location

Filter Location in hydraulicsTypes of ReservoirThere are basically two types of reservoirs:1. Non-pressurized reservoir2. Pressurized reservoirNon Pressurized Reservoir

Function of a BaffleEssentially the baffle plate performs the following functions: It permits foreign substances to settle at the bottom It allows entrained air to escape from the fluid It prevents localized turbulence in the reservoir It promotes heat dissipation from the reservoir walls.Sizing of TankThe sizing of the reservoir is based on the following criteria: It should have sufficient volume and space to allow the dirt and metal chips to settle and the air to escape freely. It should be capable of holding all the fluid that might be drained from the system. It should be able to maintain the fluid level high enough to prevent air escaping into the pump suction line. The surface area of the reservoir should be large enough to dissipate the heat generated by the system. It should have sufficient free board over the fluid surface to allow thermal expansion of the fluid.For most hydraulic systems, a reservoir having a capacity of three times the volumetricflow rate of the pump has been found to be adequate.Pressurized reservoirsAlthough it has been observed that non-pressurized reservoirs are the most suitable ones in a hydraulic system, certain hydraulic systems need to have pressurized reservoirs due to the nature of their application.

For example, the Navy's aircraft and missile hydraulic systems essentially need pressurized reservoirs in order to provide a positive flow of fluid at higher altitudes where lower temperatures and pressure conditions are encountered.