Subject- Fluid Mechanics, ppt on mechanical guages pressure measuring devices.

1. FLUID MECHANICS
Fluid Statics
(Pressure Measuring Devices)
Mechanical Gauges
Lecture 5 (BTME301-18)

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

5. Bourdon Tube Pressure Gauge
Principle:- The bourdon tube works on a simple
principle that a bent tube will change its shape
• As pressure is applied internally, the tube straightens
and returns to its original form when the pressure is
released .
• The tip of the tube moves with the internal pressure
change and is easily converted with a pointer onto a
scale.

6. Bourdon Tube Pressure Gauge

7. Diaphragm
The diaphragm is a flexible disc, which can be either
flat or with concentric corrugations and is made from
sheet metal with high tolerance dimensions.
• The diaphragm can be used as a means of isolating
the process fluids, or for high pressure applications.
• It is also useful in providing pressure measurement
with electrical transducers (LVDT).

8. Diaphragm

9. Advantages of Diaphragm
Good for low pressure
Inexpensive
Wide range
Reliable and proven
Used to measure gauge, atmospheric and differential
pressure.

10. Bellows
• A bellows gauge contains an
elastic element that is a
convoluted unit that expands
and contracts axially with
change in pressure.
• The pressure to be measured
can be applied to the outside
or inside of the bellows
however, in practice, most
bellows measuring devices
have the pressure applied to
the outside of the bellows.

11. THANKS