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Friday, 26 December 2014

PRINCIPLES OF HYDRAULICS

I have observed in my industrial life that we are very much dependent over the hydraulic driven machinery due to lots of advantage and better productivity as compared to mechanically driven machines.

I have observed lot of times, we always think why our system failed in short period of time and our team always tried to get the root cause analysis and finally we have secured some common reason and those reasons, i will explain over here and i would appreciate if readers will share their experiences about hydraulic system as we may amend the maintenance quality of our system .

I would like to mention here ,if we are not aware that our hydraulic system require special attention then this cycle will be continued of repairing and breakdown

in this blog we will introduce hydraulic principle and we will go ahead in hydraulic system with practical knowledge in our next post, we will start hydraulic system from very basic and will secure the ability for repairing and maintaining the healthiness of our hydraulic system.
so , lets start to understand how one hydraulic system operates and over which principles they are based .

Hydraulic is basically the study of forces and movement which is provided by liquids . let us understand the  hydro mechanics which is classified in Hydro statics and Hydrodynamics.
Hydro-statics pressure is given by following formula

PS= ρ * g * h

Where ,
PS = Hydro-static pressure (Bar or Pa)
ρ   = Density of liquid  ( Kg/m3 )
h   = Height of liquid (meter)
g   = Acceleration due to gravity ( 9.81 m /s2 )

Hydro-static pressure depends on the density of liquid and height of the liquid , we must note that pressure does not depend on shape of vessel that we are using.


Pascal's  Law

Let us consider following figure , where one force F1 is acting over the enclosed fluid i.e liquid via an area A1
hence ,there will be produce one pressure , P and which will be given by following formula

P = F1/A1

as we know that hydraulic system operates at high pressure hence we may neglect hydro-static pressure , hence in order to understand the pressure in liquid ,we will concentrate only pressure due to external forces.

Value of pressure in liquid will remain same throughout the liquid in all direction and we must note it that complete hydraulic system is based on this concept and this concept is known as Pascal's Law

Let us understand, how hydraulic system is based on pascal's Law

as we know that pressure at every point in enclosed liquid will be same and hence there is no matter that what is shape of vessel or container in which liquid is placed.

in order to understand how hydraulic system depends over pascal's law , we will consider following case.
P1= F1/A1
And 
P2= F2/A2

According to Pascal's law 
P1= P2



F1/A1 = F2/A2

F1 =F2 [A1/A2]

as we may see in above figure, area A2 is larger as compared to area A1 hence we will require less force to lift the heavy load .

This is the basic principle which is used by all hydraulic system .

Flow rate

Flow rate, as name indicates , is the volume of liquid flowing per unit of time or we may say in easy way flow rate means liters of liquid flowing in given period of time
Flow rate = Volume of liquid / time

Q = V / t

where ,
Q = Flow rate ;  unit = m3/s
V = Volume of liquid : unit = m3
t = Specified Time : seconds or s

Continuity equation

Q =  A. V
where ,

A = Pipe cross section area : unit = m2
V = flow velocity ; unit = m/s

Temperature measurement

In hydraulic system , temperature could be measured by using measuring devices that will send signal after sensing temperature to the control system.

We must understand that there will be premature aging of liquid ( hydraulic fluid ) if the temperature of hydraulic system fluid will be beyond manufacturer limit and due to high temperature the viscus property of fluid also reduces, hence we must maintain the temperature of liquid under specified limit as per manufacturer or up to 60 Degree centigrade. 

Resistance temperature detectors or RTDs are normally used these days in hydraulic system for sensing temperature of hydraulic fluid.

Fluid Flow

let us remind the concept of type of fluid flow , Laminar flow and turbulent flow .
As we are very well aware that for determining the type of flow we use to calculate the Reynolds number and on the basis of Reynolds number we use to decide the flow type

Value for Reynolds number might be calculated with the help of following formula

Re = ρ V D /μ

V = Flow velocity of the Hydraulic fluid i.e liquid (m/s)
D = The diameter of pipe (m)
μ = viscosity ( poise )

once we will determine ,Reynolds number

• laminar flow: Re < 2300
• turbulent flow: Re > 2300

Lets move towards next post '' Hydraulic Fluid "

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