Measurement of Pressure
Manometry
• Use liquid column in vertical or inclined tubes
• Hg barometer is an example of one type of manometer
• Measure
• 3 common types of manometers including the U-tube
manometer, piezometer, inclined manometer Measurement
of Pressure Manometry
pA  h1
p  h  p0
•Piezometer is simple and accurate
•Piezometer is only suitable if the
pressure in the container is greater
than atmospheric pressure
•Fluid in the container in which the
pressure is measured must be a
liquid rather than gas
Figure 2.9 (p. 51)
Piezometer tube.
Figure 2.10 (p. 51)
Simple U-tube manometer.
pA  h1   h2  0
pA    h2  h1
Example 1
• A manometer is used to measure the pressure in tank as
shown. If the local atmospheric pressure is 96 kPa,
determine the absolute pressure within the tank.
Example 2
A closed tank contains compressed air and oil (SGoil=0.90)
as Is shown in the Figure. h1=36 in., h2=6 in, h3=9 in.
Determine the pressure reading (in psi) of the gage using
the U-tube Hg manometer
Figure 2.11 (p. 53)
Differential U-tube manometer.
• suitable to measure the pressure
difference between two points
pA  h1    h2   h3  pB
pA  pB    h2   h3  h1
Figure 2.12 (p. 54)
Inclined-tube manometer
Suitable to measure small pressure changes
Often used to measure small difference in gas pressures
pA  h1   l2 sin    h3  pB
pA  pB   l2 sin    h3  h1
p A  pB
l2 
  sin 
pA  pB   l2 sin 
Other Pressure Measurement Devices
• Mechanical and electronic pressure measuring devices
Figure 2.13 (p. 55)
(a) Liquid-filled Bourdon pressure gages forv arious
pressure ranges. (b) Internal elements of Bourdon gages.
The “C-shaped” Bourdon tube is shown on the left, and the
“coiled spring” Bourdon tube for high pressures of 1000 psi
and above is shown on the right. (Photographs courtesy of
Weiss Instruments, Inc.)
Pressure Transducer
• Pressure is measured as an electrical output for continuous
monitoring.
Figure 2.14 (p. 56)
Pressure transducer which combines a linear variable
differential transformer (LVDT) with a Bourdon gage.
(From Ref. 4, used by permission.)
Figure 2.15a (p. 57)
(a) Two different sized strain-gage pressure transducers
(Spectramed Models P10EZ and P23XL) commonly used to
measure physiological pressures. Plastic domes are filled with
fluid and connected to blood vessels through a needle or
catheter. (Photograph courtesy of Spectramed, Inc.
Hydrostatic force on a Submerged Plane
Surface
Figure 2.16 (p. 58)
(a) Pressure distribution and resultant hydrostatic force on
the bottom of an open tank. (b) Pressure distribution on the
ends of an open tank.
Figure 2.17 (p. 58)
Notation for hydrostatic force on an inclined plane surface
of arbitrary shape.
Hydrostatic force on an inclined surface
dF  hdA, orFR   hdA
A
 y sin  dA; h  y sin 
A
FR  hc A
First moment of the area
 ydA  y
c
A
A
FR   sin   ydA
A
Hydrostatic force on a curved surface
Figure 2.23 (p. 67)
Hydrostatic force on a curved surface.