This document discusses pressure measurement. It defines pressure as the force exerted by a fluid per unit area. Absolute pressure is measured with respect to zero pressure, while gauge pressure is absolute pressure minus atmospheric pressure. Pascal's Law states that pressure is equally distributed in all directions in a static fluid. Hydrostatic law relates pressure, depth, and fluid density. Manometry uses hydrostatic law to measure pressure by relating the height of a fluid column to pressure. Common pressure measurement instruments include piezometers, manometers, and pressure transducers such as capsules, bellows, bourdon tubes, and LVDT transducers, which convert pressure into mechanical movement.

1. Fluid Mechanics
UNIT 1
Chapter 2: Pressure Measurement
ANKITENDRAN MISHRA
Asst. professor

2. Introduction to PRESSURE
 Pressure is defined as the force exerted by
the fluid per unit area. (compressive
nature)
 Unit = N/m2 or bar
 Static fluid has no shear force, only
normal force is present.
 Pressure exerted by environmental mass is
atmospheric pressure (1.01325 bar, 15ºC)

3. Gauge pressure
 Pabs=Pgauge + Patms. Absolute pressure
is measured with respect to zero pressure.
 Pressure less than atmospheric pressure is
vaccum pressure.
 There can be +ve or –ve gauge, but noe
negative absolute pressure.
 Which instrument is used to measure
the atmospheric pressure?

4. Pascal’s Law
 The pressure at a point is equal in all
directions in a static fluid (or) pressure
applied at a point is equally distributed in
all directions.
 Applicable if SF=0
 Also in ideal flowing fluid.

5. Hydrostatic law
 Gives variation of pressure in vertical
direction.
𝑑𝑝
𝑑ℎ
= w
 Pressure at any depth ‘h’
P=ρgh
 Pressure geing a function of only ‘h’, is
sometimes expressed in terms of height of
fluid coloumn.

6. Manometry
 The principle of finding pressure by using
hydrostatic law.
 Some commonly used:
I. Piezometer – used for moderate liquid
pressure measurement only
II. Manometers – Simple manometers
Differential manometers

7. Piezometers

8. Pressure Transducers
 Classified into
I. Gravitational type – simple manometers
II. Elastic type – capsule, bellows and
bourdon
CAPSULE – consists of two annular
corrugated metal diaphragm. For larger
displacement multiple capsule elements are
used in tandem.

9. BELLOWS – used for low pressure
measurement. Thin walled cylindrical shell
with deep convolutions.
Materials used for fabrication is
 Beryllium copper
 Nickle alloys
 Phosphor Bronze
 Stainless Steel

10. Bourdon- curved or twisted metallic tube
with elliptical cross section
They have high sensitivity and good
repeatability.
They are shaped in
 C-shaped – mechanical pointer
 Helical- 5 to 10 turns
 Spiral
 Twisted

11.  The deflection of bourdon pressure gauge
depends upon:
1. Internal and external pressure difference
2. Radius of curvature
3. Tube length
4. Ratio of minimum to major cross
sectional area
5. Angle of twist

12. LVDT Transducers
 Bourdon or diaphragm is coupled to the
core of LVDT.
 On application of pressure diaphragm
deflects and movement of core takes
place.