Pressure Measurement

1. PETROCHEMICAL ENGINEERING DEPARTMENT
GP313-PROCESS
INSTRUMENTATION & CONTROL
PREPARED BY:
MOHD TAUFIK REZZA BIN MOHD FOUDZI
Jun 2011

2. Pressure Measurement
FORWARD
Hydrostatic
Pressure
BACK
Pressure
HOME
FIRST Type of
SLIDE
Pressure Measurement
LAST
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Measuring
Buoyancy
Instruments
Applications Evaluation

3. PRESSURE
FORWARD
• Pressure units are a measure of force
BACK acting over unit area.
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• It is most commonly expressed in
pounds per square inch (psi) or
FIRST
SLIDE sometimes pounds per square foot (psf)
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SLIDE
in English units; or Pascals (Pa) in
metric units, which is the force in
Newtons per square meter (N/m²).
Pressure = Force, F Exercise
Area, A 2.1

4. HYDROSTATIC PRESSURE
FORWARD
BACK
A B C
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LAST
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Which the vessels above have
high pressure?

5. HYDROSTATIC PRESSURE
FORWARD
• A vertical column of fluid exerts a pressure due
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to the column’s weight.
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• The relationship between column height and
fluid pressure at the bottom of the column is
FIRST
SLIDE constant for any particular fluid (density)
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regardless of vessel width or shape.
Exercise
2.2, 2.3
= Mass density of fluid in kilograms per cubic meter (metric)
or slugs per cubic foot (British)
=Weight density of fluid in Newton per cubic meter (metric)
or pounds per cubic foot (British)

6. SPECIFIC WEIGHT TABLE
FORWARD
BACK
HOME
FIRST
SLIDE
LAST
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7. TYPE OF PRESSURE MEASUREMENT
FORWARD
BACK
Atmosphere Pressure
HOME
FIRST
SLIDE Vacuum Absolute
LAST Pressure Pressure
SLIDE
Gauge
Pressure

8. PRESSURE CONVERSION
FORWARD
BACK
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Exercise
2.5, Extra

9. BUOYANCY
FORWARD
•Buoyancy is the upward force exerted on an object
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immersed or floating in a liquid.
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•The weight is less than it is in air, due to the weight of the
displaced fluid. The upward force on the object causes the
FIRST
SLIDE
weight loss, called the buoyant force, and is given by:
LAST
SLIDE
where
B = The buoyant force in pounds
y = The specific weight in pounds per cubic foot
V = the volume of the displaced liquid in cubic feet.

10. BUOYANCY
FORWARD
BACK
HOME
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LAST
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Exercise
2.6, 2.7

11. PASCAL LAW
FORWARD
The pressure applied to an enclosed liquid (or
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gas) is transmitted to all parts of the fluid and to
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the walls of the container.
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LAST
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Exercise
2.8

12. MEASURING INSTRUMENTS
FORWARD
BACK
HOME
FIRST
SLIDE Manometer
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Exercise
2.9, 2.10

13. MEASURING INSTRUMENTS
FORWARD
BACK Diaphragms, The devices that change
Capsules, their shape when pressure
HOME
and Bellows is applied.
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LAST
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14. MEASURING INSTRUMENTS
FORWARD
BACK
Capsules
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FIRST
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LAST
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15. MEASURING INSTRUMENTS
FORWARD
BACK
Bellow
HOME
FIRST
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LAST
SLIDE

16. MEASURING INSTRUMENTS
FORWARD
BACK
Bourdon
Tube
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FIRST
SLIDE
LAST
SLIDE

17. MEASURING INSTRUMENTS
FORWARD
BACK
HOME
FIRST
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LAST
SLIDE Differential
Pressure
Transmitter

18. Applications
FORWARD
Measuring process vessel clogging
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HOME
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LAST
SLIDE

19. Applications
FORWARD
Measuring positive gauge pressure
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HOME
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LAST
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20. Applications
FORWARD
Measuring vacuum
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HOME
FIRST
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LAST
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21. EXERCISE 2.1
FORWARD
BACK The liquid in a container has a total weight of 152
HOME
kN, and the container has a 8.9 m² base. What is
the pressure on the base?
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LAST
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BACK >>

22. EXERCISE 2.2 & 2.3
FORWARD
BACK What is the depth in a lake, if the pressure is 0.1
HOME
MPa?
FIRST
SLIDE What is the pressure at the base of a water tower
LAST that has 35m of head?
SLIDE
BACK >>

23. EXERCISE 2.5 & EXTRA
FORWARD
BACK What pressure in psi corresponds to 98.5 kPa?
HOME
FIRST
The atmospheric pressure is 14.5 psi. If the
SLIDE absolute pressure is 2,865.6 psfa, what is
LAST
SLIDE
the gauge pressure?
What is the gauge pressure in (a) kPa, and (b)
N/cm², at a distance 5.5 ft below the
surface of a column of water?
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24. EXERCISE 2.6 & 2.7
FORWARD
BACK
What is the buoyant force on a plastic cube with
2.5m sides, floating in water, if three-quarters of
HOME the block is submerged?
FIRST
SLIDE
What is the apparent weight of a 3.7m³ block of
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SLIDE wood totally immersed in acetone? Assume the
specific weight of wood is 8.5 kN/m³.
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25. EXERCISE 2.8
FORWARD
BACK
In figure below, if the area of the small piston A S is
8.2 in²,and the area of the large piston A L is 2.3 ft²,
HOME what is the force FL on the large piston, if the force
FIRST FS on the small piston is 25N?
SLIDE
LAST
SLIDE
BACK >>

26. EXERCISE 2.9 & 2.10
FORWARD
BACK
The liquid in a manometer has a specific weight of
8.5 kN/m³. If the liquid rises 83 cm higher in the lower
HOME pressure leg, what is difference in the pressure
FIRST between the higher and the lower legs?
SLIDE
LAST
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What is the liquid density in a manometer, if the
difference in the liquid levels in the manometer
tubes is 1.35m, and the differential pressure
between the tubes is 7.85 kPa?
BACK >>