The document defines pressure as the force exerted on a unit area and describes different types of pressure including atmospheric and gauge pressure. It discusses the measurement of atmospheric pressure using barometers and the use of manometers and mechanical gauges for measuring fluid pressure, noting that piezometers are a simple type of manometer for moderate pressures. Additionally, it outlines the requirements for manometric fluids depending on the pressure range being measured.

1. 1
Definition of
Pressure
Pressure is defined as the amount of force
exerted on a unit area of a substance:
Pa
m
N
area
force
P 

 2

2. 2
ATMOSPHERIC PRESSURE
VACUUM PRESSURE
GAUGE PRESSURE
ABSOLUTE PRESSURE
ABSOLUTE ZERO PRESSURE
PRESSURE
A
B
RELATIONSHIP BETWEEN PRESSURES
101,325 Pa
0 Pa

3. 3
Measurement of Atmospheric Pressure
Atmospheric pressure is measured by a device called a barometer;
Patm = ρgh

4. 4
It is important to note that the pressure of a
fluid can be measured either using:
Manometers
or
Mechanical gauges

5. 5
The pressure of a fluid is measured in
Manometers by balancing the column of a
fluid by the same or another column of fluid,
Whereas, the pressure of a fluid is measured
in Mechanical Gauges by balancing the fluid
column by spring or dead weight.

6. 6
The mechanical gauges are used for measuring
high pressure and where high precision is not
required.
Some examples of mechanical gauges are as
follows:
Bourdon Tube Pressure gauge
Diaphragm Type Pressure gauge
McLeod Gauge
Dead Weight Pressure Gauge
However, in dealing with low pressure of fluids, we
will use manometer only for the measurement of
pressure.

7. 7
The simplest manometer used for the
measurement of pressure- Piezometer.
A Piezometer is the simplest form of
Manometer, which is used for the
measurement of moderate pressure of a
liquid.

8. 8
It consists of a glass tube inserted in the wall
of a vessel or of a pipe containing liquid
whose pressure is to be measured.
The tube extends vertically upwards to such a
height that the liquid can freely rise in it
without overflowing.
The arrangement is shown in the figure.

9. 9

10. 10

11. 11
A simple manometer is the device consisting
of a glass tube bent in u shape.
One end of the tube is connected to a point
at which the pressure of the fluid is to be
measured, and the other end is left open to
the atmosphere.
SIMPLE
MANOMETER

12. 12 Positive Gauge Pressure. Vacuum Pressure
ρl
ρHg
ρHg
ρl
Patm
Patm
SIMPLE MANOMETER

13. 13
SIMPLE MANOMETER

14. 14
SINGLE COLUMN MANOMETER

15. 15
INCLINED SINGLE COLUMN MANOMETER
More Sensitive

16. 16
DIFFERENTIAL MANOMETER
ρ1
ρg

17. 17
ρ1
ρg

18. 18
INVERTED U TUBE DIFFERENTIAL MANOMETER
Uses lighter manometric liquid
=

19. 19
MICROMANOMETER

20. 20
Requirements of manometric fluid
For Higher pressure measurement
Liquids should be immiscible
Liquid should have high density
Liquid should have low vapor pressure
Should not wet glass surface
For Lower pressure measurement
Liquids should be immiscible
Liquid should have low density
Liquid should have low vapor pressure
Should not wet glass surface

21. 21
Bourdon tube