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5.5 Flushing Pipes
To remove dust, other particles and moisture, which
could cause compressor malfunction if not flushed out
before the system is run, the refrigerant piping should
be flushed using nitrogen. Pipe flushing should be
performed once the piping connections have been
completed with the exception of the final connections to
the indoor units. That is, flushing should be performed
once the outdoor units have been connected but before
the indoor units are connected.
CAUTION
Only use nitrogen for flushing. Using carbon
dioxide risks leaving condensation in the piping.
Oxygen, air, refrigerant, flammable gases and
toxic gases must not be used for flushing. Use of
such gases may result in fire or explosion.
The
liquid
and
gas
sides
simultaneously.
The flushing procedure is as follows:
1.Cover the inlets and outlets of the indoor units to
prevent dirt getting blown in during pipe flushing. (Pipe
flushing should be carried out before connecting the
indoor units to the piping system.)
2.Attach a pressure reducing valve to a nitrogen cylinder.
3.Connect the pressure reducing valve outlet to the inlet
on the liquid (or gas) side of the outdoor unit.
4.Use blind plugs to block all liquid (gas) side openings,
except for the opening at the indoor unit which is furthest
from the outdoor units ("Indoor unit A" in Fig.5.34).
5.Start to open the nitrogen cylinder valve and gradually
increase the pressure to 0.5Mpa.
6.Allow time for nitrogen to flow as far as the opening at
indoor unit A.
7.Flush the first opening:
a)Using suitable material, such as a bag or cloth, press
firmly against the opening at indoor unit A.
b)When the pressure becomes too high to block with
your hand, suddenly remove your hand allowing gas to
rush out.
c)Repeatedly flush in this manner until no further dirt or
moisture is emitted from the piping. Use a clean cloth to
check for dirt or moisture being emitted. Seal the
opening once it has been flushed.
8.Flush the other openings in the same manner, working
in sequence from indoor unit A towards the outdoor
units. Refer to Fig.5.35
9.Once flushing is complete, seal all openings to prevent
dust and moisture from entering.
liquid pipe
gas pipe
Outdoor
unit
Indoor
Indoor
unit A
unit B
must
be
flushed
Fig.5.34
5.6 Gas Tightness Test
To prevent faults caused by refrigerant leakage, a gas
tightness test should be performed before system
commissioning.
NOTE
Only dry nitrogen should be used for gas
tightness testing. Oxygen, air, flammable
gases and toxic gases must not be used for
gas tightness testing. Use of such gases may
result in fire or explosion.
Make sure that all the outdoor unit stop
valves are firmly closed.
Make sure all piping connections are
complete before the tightness test begins.
The gas tightness test procedure is as follows:
1.Charge the indoor piping with nitrogen at 0.3Mpa
through the needle valves on the liquid and gas stop
valves and leave for at least 3 minutes (do not open the
liquid or gas stop valves). Observe the pressure gauge
to check for large leakages. If there is a large leakage,
the pressure gauge will drop quickly.
2.If there are no large leakages, charge the piping with
nitrogen at 1.5Mpa and leave for at least 3 minutes.
Observe the pressure gauge to check for small
leakages. If there is a small leakage, the pressure gauge
will drop distinctly.
3.If there are no small leakages, charge the piping with
nitrogen at 4.2 MPa and leave for at least 24 hours to
check for micro leakages. Micro leakages are difficult to
detect. To check for micro leakages, allow for any
change in ambient temperature over the test period by
adjusting the reference pressure by 0.01Mpa per 1°C of
temperature difference. Adjusted reference pressure =
Pressure at pressurization + (temperature at observation
– temperature at pressurization) x 0.01Mpa. Compare
the observed pressure with the adjusted reference
pressure. If they are the same, the piping has passed the
gas tightness test. If the observed pressure is lower than
the adjusted reference pressure, the piping has a micro
leakage.
4.If the leakage is detected, refer to following part "Leak
detection". Once the leak has been found and fixed, the
gas tightness test should be repeated.
5.If not continuing straight to vacuum drying once the
gas tightness test is complete, reduce the system
pressure to 0.5-0.8MPa and leave the system
pressurized until ready to carry out the vacuum drying
procedure.
Outdoor unit
Liquid side of
Gas pipe
Liquid pipe
stop valve
Gas side of
stop valve
Nitrogen
Indoor unit
Fig.5.35
V.1
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