Download GENERAL RULES FOR HANDLING REFRIGERANT GAS

PRESSURE
MEASUREMENT
INSTRUMENTS
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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Hello, I want to show you the various
pressure measurement gauges we
use at Fresh or Freezing and talk
about how we maintain and test them.
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Normally we aren’t looking for exact
pressures – rather we need to know
the pressure differences between the
high side and the low side of a
system. To do this we use a few
different types of gauges.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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The type of gauge used on a
refrigeration service manifold gauge
set is the Bourdon tube gauge. This
is used for indicating system
pressures. The gauge manifold is
fitted with two gauges.
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The pressure gauge (red) only
measures high side system
pressures above 0 kPa
(atmospheric pressure).
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The compound gauge (blue)
measures low side system
pressures above or below 0 kPa.
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Most gauges with an indicating
needle are Bourdon tube gauges.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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For measuring very small
pressures of less than 1 kPa a
manometer or a magnehelic
gauge is used. This is used for
measuring the pressure drop
across air conditioning filters or
duct pressures.
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This is a digital manometer
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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There are two types of monometer
gauges we use at Fresh or Freezing.
They are U tube monometers and
inclined monometers.
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U tube manometers are filled with
mercury and are used for measuring
pressure drops across water cooled
condensers, chilled water and hot water
coils and chillers (mmHg).
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U tube manometers can also be filled with a coloured
manometer fluid to measure static pressure differences across
air handling systems (Pa).
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Inclined manometers are filled with coloured manometer fluid
and used to measure pressure drops of air across filters. They
are also used to measure ductwork static pressures and
velocity pressures to determine air flow rates (Pa).
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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As part of our work we need to
measure vacuums. In the field,
vacuums are measured with
electronic vacuum gauges.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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We also need to
measure atmospheric
pressure. To do this we
use a barometer.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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All our equipment and tools have to
be stored and maintained properly
so they give us accurate readings. I
always make sure they are clean
and placed in their correct storage
place when I’ve finished using them.
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Generally Bourdon tube gauges are
reasonably rugged and will require
little in the way of regular
maintenance. A periodic test for
leaks is good practice.
Calibration usually consists of removing any residual
refrigerant, in keeping with the current codes of good
practice, then adjusting the needle of the gauge to read 0
kPa at atmospheric pressure.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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As gauges are usually fitted to a
service manifold, maintenance
includes replacing the rubber seals
in the ends of the gauge lines, and
giving the gauge lines a visual
check to look for perishing of the
lines, cracks in the outer covering of
the lines, and any other signs of
mechanical damage.
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Keep gauge lines sealed to keep
out dirt and other contaminants.
Other types of pressure gauges require specialised
maintenance which must be carried out by suitably qualified
persons.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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When taking readings, be careful.
You will be working on an operating
unit. You need to be aware of
rotating machinery, as well as the
fact that some components will be
very hot or cold. The refrigerant in
the gauge lines and the system
may be at high pressure and can
cause burns and damage the ozone
layer if it escapes.
You need to be careful to avoid the gauge needles
bouncing from the refrigerant oscillation, especially in the
high side, as this will cause damage to the gauge
mechanism.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence
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Remember:
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The red gauge is fitted to the high
side of the system as it is a
pressure gauge, ie it only reads
pressures above 0 kPa.
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The blue gauge is fitted to the low
side of the system as it is a
compound gauge. It reads
pressures above and below 0 kPa.
© Commonwealth of Australia 2010 | Licensed under AEShareNet Share and Return licence