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04/22/2023 Introduction to Hydraulic Power

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INTRODUCTION TO FLUID POWER

By ,

Royson Donate DsouzaAsst. Professor , Manipal School of Engineering-Dubai Campus


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INTRODUCTION TO HYDRAULIC POWER

• Introduction

• Objectives

• Fluid Power

• Fluid flow fundamentals

• Pascal Law

• Hydraulic force transmission

• Components of a Hydraulic System

• Summary

• Reference


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INTRODUCTION TO HYDRAULIC POWER

• Hydraulics and Pneumatics is the technology that deals

with the generation, control and transmission of power

using pressurized fluid. This subject is designated as FLUID

POWER, and is world wide accepted.

• The word Hydraulics is derived from the Greek

word ‘HYDOR’ means ‘Water’. This comprised all things

in affiliation with ‘Water’.

• The word Pneumatics is derived from Latin

Word “PNEUMO” means “Breathing”.


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Applications Include:

• It jacks up an automobile (Hydraulic jack)• Drills out teeth• Launches space ship • Control submarines • Mines coals and ores • Moves earth (earth moving equipment like excavators,

bull-dozers, bore-well drills etc.,) • Harvest crops • Presses • Machine tools • Material handling equipment • Transportation • Construction• And in general, makes our everyday living easier and more

enjoyable.

INTRODUCTION TO HYDRAULIC POWER (Cont.)


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By the end of this chapter you will be able to:

1. Understand Fluid Power

2. Know Fluid flow fundamentals

3. Explain Pascal Law

4. Learn about Hydraulic force transmission

5. Know the Components of a Hydraulic System

OBJECTIVES


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• Fluid power provides flexible and easy control of variable force, distance and speed.

• Fluid power can be varied from a delicate touch of a few grams to a gigantic force of 36000 tons or more.

• Hydraulic system use liquids such as petroleum oils, water, synthetic oils etc. The first hydraulic fluid to be used was water because it is readily available but it has been replaced by oils.

• Pneumatic system use air as the gas medium because air is very abundant and can be readily exhausted into the atmosphere.

FLUID POWER


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The field of fluid mechanics is broken down as follows:

1. Hydrostatics

2. Hydrodynamics

FLUID FLOW FUNDAMENTALS


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• It is the pressure which acts on the base of container filled with fluid and is dependent on the height of head of fluid inside the container.

• Mathematically , p = ρgh

Where ρ = mass density, Kg/m3

h = height of fluid level (head) in m

p = pressure intensity in bar, 1 bar = 105 Pascal = 105 N/m2

g = acceleration due to gravity, m/s2

MECHANICS OF STILL FLUID


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• Which section has the highest pressure intensity????

BRAIN TEASER!!!!!!!!


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• Which section has the highest pressure intensity????

Ans: The pressure intensity at all points along a horizontal plane remains the same; p1= p2 = p3

BRAIN TEASER!!!!!!!!


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• It is related to mechanics of moving fluid. It is concerned with the fluid flow laws and their effective forces.

a) Continuity equation: In steady state, the mass of fluid passing through all cross section of a tube / unit time is the same.

i.e, ρ1A1v1 = ρ2A2v2

Since ρl = ρ2

(same fluid is flowing in the pipe) Where v1,v2 = velocity of flow, m/s at cross section 1 and 2. A1, A2 = cross sectional area at section 1 and 2.

Fluid flow fundamentals (Contd.)

A1v1 = A2v2


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• Flow rate Q = V/ t , V = volume = A * S, where S = distance , t = time

i.e, Q = A * S/t

Distance s divided by time t is the quotient velocity v

i.e, v = A * V

therefore , Q = A * v

From 1, Q= A1v1 = A2v2 = Constant which is the continuity equation.

Also Q is proportional to square root of pressure across the length

i.e.,


𝑄∝√∆ 𝑃


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Question 1.• A hydraulic press has a ram of 30cm of diameter

and a plunger of 4.5cm diameter. Find the weight lifted by the hydraulic press when the force applied at the plunger is 500N. F

W

RAM

PLUNGER

`


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Homework Questions.

1. A hydraulic press has a ram of 20cm diameter and a plunger of 3cm diameter. It is used for lifting a weight of 50kN. Find the force required at the plunger.


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• Bernoulli’s equation:It states that the total energy of a flow of fluid does not change as long as energy is not supplied from the outside or transferred to the outside.

Total energy is made up of:

1. Potential energy2. Pressure energy and dependent on the column of fluid and on static pressure.3. Kinetic energy: It is dependent on the velocity of flow and on back pressure.



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Hence, Ptotal = Z + p / rg + v2/ 2g

Where Z =elevation

p= Pressure of fluid

v= Velocity of flow

r = Density of fluid



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Friction and Pressure losses :

If the fluid is still (no fluid movement), then pressure is same at all the point.

If fluid is flowing through the system, heat is created by friction. Thus part of energy is lost as heat energy, which means loss of pressure. The amount of friction loss is related to

Length of pipe Roughness of the pressure Cross sectional area of pipe Number of pipe bends Velocity of fluid flow Viscosity of fluid flow


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Types of flow :

Laminar flow: Up to a certain velocity fluid moves along pipes in layers (Laminar). The inner most fluid layer travels at the highest speed. The outer most fluid layer at the pipe wall does not move.


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Types of flow :

Turbulent flow: If the velocity of flow is increased, the type of flow changes at the critical velocity and becomes turbulent. This results in an increase of flow resistance and thus the hydraulic losses increases. Therefore, turbulent flow is not usually desirable.


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Reynolds’s number Re:The type of flow may be roughly determined Using Reynolds’s number

Re = v * dh /u

Where v = Velocity of flow m/s dh = Hydraulic diameter in m, with circular cross- sections equal to the pipe internal diameter, and otherwise calculated as

dh = 4 * A/U A = Cross- sectional area, U = Circumference u = Kinematic viscosity in m2/s and


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Recrit = 2300

At Recrit the type of flow changes from laminar to turbulent and vice versa.Laminar flow occurs for Re < Recrit , and

Turbulent flow occurs for Re> Recrit


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Pascal Law

Fluid power technology actually began in 1650 with the discovery of Pascal Law. Simply this law says that “Pressure in a fluid at rest is transmitted equally in all directions“

This law states “A pressure added to a confined fluid is transmitted undiminished throughout the fluid”.

It acts on all surfaces in a direction at right angle to those surfaces. The amount of pressure in the fluid is equal to the weightforce with respect to the area being acted upon.

Mathematically, it is defined as Pressure = Force / Area; i.e., p = F / A


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Hydraulic force transmission

• As pressure distributes equally in all directions, the shape of the container is irrelevant. If we now pressurise surface A1 with force F1, we create pressure, p = F1 / A1

• Pressure acts on all sides equally and simultaneously. It is therefore equal at all points. Therefore, it acts also on surface A2 The force which can be achieved is F2 = p A2

Thus F1 / A1 = F2 / A2

Or F2 / F1 = A2 / A1

• The pressure in such a system always depend on the size of the load and effective surface. This means that the pressure rises until it can overcome the resistance, which builds up in opposition to the fluid movement.

• The relationship of the paths S1 and S2 of the two pistons is then opposite to that of the surface. i.e., S1 / S2 = A2 / A1


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Advantages of using Fluid Power

• Fluid power provides flexibility in the control of machines

• Fluid power provides high forces (torque) with compact size i.e., high power density.

• Stepless regulation of speed.

• Simple overload protection.

• Suitable for controlling fast movement and for extremely slow precision movement.

• Hydraulic provides automatic lubrication for less wear.

• Pneumatic system is clean and safe from fire hazards.

• Fluid power is simple and provides ease of installation and maintenance.


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Components of a Hydraulic System

• The hydraulic actuator• The hydraulic pump• Valves• External power supply (motor)• Reservoir• Piping system• Filters• Pressure regulator


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• 1. 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.

• 2. 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.

• 3. Valves are used to control the direction, pressure and flow rate of a fluid flowing through the circuit. Motor 1 – Off 2 – Forward 3– Return 3 2 1 Load Direction control valve Pump Oil tank Filter Actuator Pressure regulator

• 4. External power supply (motor) is required to drive the pump.

• 5. Reservoir is used to hold the hydraulic liquid, usually hydraulic oil.

• 6. Piping system carries the hydraulic oil from one place to another.

• 7. Filters 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. 8. Pressure regulator regulates (i.e., maintains) the required level of pressure in the hydraulic fluid.


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Summary

We have learnt a considerable amount of information aboutFluid power :

Fluid flow fundamentals

Pascal Law

Hydraulic force transmission



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Exercise:

1. Distinguish between Hydrostatic and Hydrodynamic fluid flow?

2. Explain Pascal Law and show that how the pressure can be transmitted?

3. State the advantages and disadvantages of Fluid Power system?

4. State the applications of Fluid Power system?

5. Discuss the various components of Fluid Power system?

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