This document discusses hydraulic principles including Pascal's law of transmission of pressure in confined fluids. It defines key terms like pressure, force and area. It explains how hydraulic systems use Pascal's law to multiply force - applying a small force over a small area creates high pressure that can generate a much larger force when applied over a larger area, like in hydraulic brakes and presses. The conservation of energy is maintained because while force is multiplied, distance of travel is reduced in inverse proportion to the increase in area and force.
2. Definition
Pressure – Force – Area relationship
Pascal’s Law
Hydraulic Press
Hydraulic Brake
Conservation of Energy
3. It deals with the transmission of force in a confined
area
It works on the principle discovered by French
scientist named Blaise Pascal
4. Pressure is the force acting on unit area it is usually
expressed in pound per square inch (PSI) or Newton
per square meter (Pascal)
5.
6. We use the Pressure–Force–Area triangle to find
relationship between them
P
7. We use the Pressure–Force–Area triangle to find
relationship between them
A
8. We use the Pressure–Force–Area triangle to find
relationship between them
F
9. Force: Pound / Newton
Area: in2 / m2
Pressure: Pound per square inch (PSI) /
Newton per square meter (Pascal)
10. Pressure applied on confined fluid is transmitted in all
directions and acts with equal force on equal area and
at right angle (90 degree) to them.
This is the basic principle behind all hydraulic systems
Simply, force applied at any point can be transmitted
to another point using incompressible liquid
11. Take a glass bottle filled with fluid.
A small input force is applied to stopper
Pressure equal to force divided by
stopper area is created in the fluid
In this cause it is 10 lb per sq inch
According to this law this developed
pressure will travel through liquid in all
direction
This pressure acts against equal area of
bottle
The resultant output force is multiplied
by the bottom area of bottle
12. Area of bottom of bottle is 20 in2
So in this case output of 200 lb force is
generated with input force of 10 lb.
Due to this increase in force the bottle
brakes
Remember as a simple rule of thumb,
In Hydraulics a small force on a small
area creates a proportionately large
force on a large area
13. What would be the pressure developed if a force of 50 lb
acts on area of 10 square inches.
500 PSI
50 PSI
5 PSI
Its 50 X 10 = 500 PSI
14. Hydraulic press uses the principle stated by Pascal’s law
We can multiply the force on small area to the force on
larger area
Hydraulic press also called Bramah press after the
inventor Joseph Bramah of England invented it in 1795 .
A force of 10 lb is applied to a piston of 1 in2.
Resultant system pressure on smaller piston is 10 PSI
This pressure is transmitted undiminished (not reduced)
through the fluid till it acts on big cylinder with area of
10 in2.
15. So resultant force on large piston is (pressure X area)
10 PSI X 10 in2 = 100 lb
This force balances the downward force of 100 lb due to
weight of the cylinder
16. A small force is applied on brake
pedal whose area is small
The pedal transmits the resultant
pressure through the hydraulic oil
Force gets multiplied on the brake
piston which has a larger area
17. The of conservation of energy states “ Energy can
neither be created nor destroyed”.
The multiplication of force in hydraulics gives the
impression that energy is being created, because of force
multiplication.
This is not the case however
As energy is measured in terms of ‘amount of work done’
And, work is defined as Work = Force X Distance
In the previous example force on small piston is
sufficient to move large piston
18. However it must be noted that smaller piston moves 10
inches to move large piston 1 inch
If the smaler piston moves by 10 inch inside container,
the volume of fluid displaced is calculated as
Volume = Piston area X Distance
= 1 in2 X 10 in
= 10 in3
Hence the amount of work accomplished or force over a
distance is same for both the pistons
This proves the energy is not created though force is
multiplied
19. The volume displaced by fluid pushes the larger piston,
the distance by which the larger piston moves is
calculated as
Distance = Volume / Piston area
= 10 in3 / 10 in2
= 1 inch
The distance each piston moved is inversely proportional
to area
From this we conclude “what is gained in force is
scarified in distance”