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Part 6
What are different types of
orifice plates? State their uses.
How do you identify an
orifice in the pipeline?
Why is the orifice tab
provided?
Explain Bernoulli’s
theorem. State its application.
How can a D.P. transmitter
be calibrated?
How is flow measured in
square root?
Name different parts of a
pressure gauge. Explain the use of hair spring in the pressure gauge.
What are different types of orifice plates? State their uses.
Different orifice plates are: 1. Concentric 2. Segmental 3. Eccentric
- Concentric: These plates are used for ideal liquid as well as gases and steam
service. Concentric holes are present in these plates, thats why it is known as
concentric orifice.
- Segmental: This plate has hole in the form of segment of the circle. This
plate is used for colloidal and sherry flow measurement.
- Eccentric: This plate has the eccentric holes. This plate is used in viscous
and sherry flow measurement.
How do you identify an orifice in the pipeline?
An orifice tab is welded on the orifice plate which extends out of the line
giving an indication of the orifice plate.
Why is the orifice tab provided?
Following reasons justify for providing orifice tab:
1. Indication of orifice plate in a line
2. The orifice diameter is marked on it.
3. The material of the orifice plate.
4. The tag number of the orifice plate.
5. To mark the inlet of an orifice.
Explain Bernoulli’s theorem. State its application.
Bernoulli’s theorem states that the ‘total energy of a liquid flowing from one
point to another remains constant’. It is applicable for non-compressible
liquids. For different types of liquid flow Bernoulli’s equation changes. There
is direct proportion between speed of fluid and its dynamic pressure and its
kinetic energy. It can be used in various real life situations like measuring
pressure on aircraft wing and calibrating the airspeed indicator. It can also
be used to low pressure in the venturi tubes present in carburetor.
How can a D.P. transmitter be calibrated?
D.P. transmitter can be calibrated using following steps:
1. Adjust zero of Xmtrs.
2. Perform static pressure test: Give equal pressure on both sides of
transmitter. Zero should not shift either side. If the zero shifts then carry
out static alignment.
3. Perform vacuum test: Apply equal vacuum to both the sides. Zero should not
shift.
4. Calibration procedure: Give 20 psi air supply to the transmitter and vent
L.P. side to atmosphere. Connect output of the instrument to the standard test
gauge. Adjust zero. Apply required pressure to the high pressure side and
adjust the span. Adjust zero gain if necessary.
How is flow measured in square root?
Flow varies directly as the square root of pressure. Thus, F=K of square root of
applied pressure. Since this flow varies as the square root of differential
pressure. The pressure pen does not directly indicate flow. Thus flow can be
determined by taking the square root of the pen. Assume the pen reads 50% of
the chart. So, flow can be calculated using the pen measure in the chart.
Name different parts of a pressure gauge. Explain the use of hair
spring in the pressure gauge.
Pressure gauge includes following components:
a. ‘C’ type bourdon tube.
b. Connecting link
c. Sector gear
d. Pinion Gear
e. Hair spring
f. Pointer
g. Dial
Use of hair spring: Hair spring is responsible for controlling torque. It is
also used to eliminate any play into linkages.
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