2. Pressure
Pressure (P) expresses the magnitude of normal force(F)
per unit area(A) applied on the surface.
SI units :- Pascal (N/m²)
Other units:- bar (=10⁵ pa), atm (=101.3kpa),
3. PRESSURE MEASURING DEVICES
The pressure of a fluid can be measured by the
following devices:
• Manometers
• Mechanical Gauges
Manometers – It is device used for measuring the
pressure at a point in a fluid by balancing the column
of fluid by the same or different column of the fluid.
They are further classified as:
• Simple Manometers
• Differential Manometers
4. PRESSURE MEASURING DEVICES
Mechanical Gauges – It is device which uses spring or
dead weight to measure pressure by balancing it with
fluid column. Commonly used mechanical pressure
gauges are:-
• Diaphragm pressure gauge
• Bellows pressure gauge
• Dead-Weight pressure gauge
• Bourdon tube pressure gauge
6. SIMPLE MANOMETERS
• A simple manometer consists of a glass tube having
one of its ends connected to a point where pressure is
to be measured and other end remains open to atm
Common types of simple manometers are :
1. Piezometer.
2. U-tube Manometer.
3. Single Column Manometer.
7. Piezometer
It is the simplest form of
manometer used for
measuring pressures. One
end of this manometer is
connected to the point
where pressure is to be
measured and other end is
open to the atmosphere as
shown in figure. The rise of
liquid gives the pressure
head at that point.
Pressure at A =⍴gh N/m²
8. U-tube Manometer
Let A be the point whose pressure is to be measured.
h1 = Height of light liquid above the datum line
h2 =Height of heavy liquid above the datum line
⍴₁ =Density of light liquid =1000*S₁
⍴₂ =Density of heavy liquid =1000*s₂
9. U-tube Manometer
• S₁ are the specific gravity of light liquid
• s₂ are the specific gravity of heavy liquid
As the pressure is the same for horizontal Surface. Hence
Pressure above the horizontal datum line A-A should be
same in both columns.
Pressure above A-A in the left column=p+ ⍴₁ *g* h1
Pressure above A-A in the right column= ⍴2 *g* h2
• Hence equating the two pressures
• p+ ⍴₁ *g* h1 = ⍴2 *g* h2
• P=(⍴2 *g* h2 - ⍴₁ *g* h1 )
