Concepts about hydraulics.

Hydraulic Systems

Physics behind Hydraulics

Ever wondered how the beautiful mechanism behind hydraulic machines work? Hydraulics as the name suggests involves the use of liquid and laws of liquid pressure to carry out work. Hydraulic machines and especially Hydraulic lifts and brakes which are hugely implemented and used in the car and technological industry involve the use of pressure in liquids and a basic idea and knowledge about physics. To understand the concept, we need to reflect back upon the basics of physical concepts.

The idea of Hydraulics involves Pascal's Law. The law proposed by Blaise Pascal (A french mathematician and physicist) states that the pressure exerted on one point (surface area) of the liquid exerts and transfers the same and equal pressure throughout the liquid. This liquid is assumed to be in a closed system i.e. "pressure exerted in a confined and incompressible fluid is transmitted equally throughout it."

                                                     

You may be wondering why choose liquids, well liquids are the best suitable for the job because they are not compressible. This unique property enables them to transfer the force, hence the pressure, equally through the liquid. 

Hydraulic mechanism involves a liquid which is used to either transfer the pressure to a braking pad or used to lift heavy load.

Here's an example of application of hydraulic pressure:

     

This hydraulic jack or lift uses a liquid (commonly known as a hydraulic fluid) to transfer the pressure. This simplified example consists of two pistons. Input Piston (on which we exert force) has a smaller area than the the output piston(on which load is kept). A force (F1) is applied on the input piston exerting pressure, as a force is applied on a unit area (A1), resulting in pressure being generated on the piston. 

[Pressure = Force/Area], thus P1 = F1/A1

This pressure is equally transmitted through the incompressible liquid to the other output piston . The output piston experiences a greater force being experienced as the pressure is exerted in a unit larger area. (A2)

Mathematically speaking,

P₁= P₂

F1/A1 = F2/A2

As,   A1<A2

F1<F2  to keep the pressure constant.

Thus the Jack/lift is a force multiplier and can lift heavier objects (with a greater mass) with a less force. In the above example:

 P1 = 1 N/ 1 cm^2 

P1 = 1 N/cm^2

P2=P1

P2 = F2/A2

F2= P2*A2 

                      = 1 N/cm^2 /*50 cm^2

F2= 50 N

Thus this jack/lift multiplies the force by 50.  Thus a force of 20 N would be required to lift an object of 1000 N - fifty times less. Thus it is hugely beneficial in hydraulic lifts and presses which are used widely in many industries.

But this extra force comes at a cost as the output piston is only moved by a factor of the distance. In the above case: (1/50)th of the distance that the input piston is pushed down.

This is due to the fact that input piston  displaces a volume of, lets say, V input cm^3. This same amount of liquid is then transferred to the output piston (V output), but due to the output piston having a larger surface area, it is moved a lot less.   

Image: https://commons.wikimedia.org/wiki/File:BernoullisLawDerivationDiagram.svg#mediaviewer/File:BernoullisLawDerivationDiagram.svg

In the above diagram, as area 1 is less than area 2. The volume of liquid is the same, the distance, L1, is more than the distance, L2. Thus the output piston moves less distance than the input piston is moved. 

Mathematically speaking,

Volume _input = Volume _Output

Area₁ * Length _input = Area₂* Length _output

When A₂>A₁, then L _output < L _input

This was, in a gist, the basic principle which governs the hydraulic machines which makes our work a lot easier.

Still confused: Watch this video

img src = google

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