VACUUM DRYING AND LEAKAGE CHECKING
18
1
.
Purpose of
vacuum
drying
Eliminating
moisture
in
system
to
prevent the phenomena of ice
-
blockage
and copper oxidation
.
Ice
-
blockage
shall
cause
abnormal
operation
of
system
,
while
copper oxide
shall
damage
compressor
.
Eliminating the
non
-
condensable
gas (air) in system
to
prevent
the
components oxidizing
,
pressure
fluctuation
and
bad
heat exchange
during
the
operation
of
system
.
2
.
Selection
of
vacuum
pump
The
ultimate
vacuum degree
of
vacuum pump shall
be
-
756mmHg
or
above
.
Precision
of
vacuum
pump
shall
reach
0
.
02mmHg
or
above
.
3
.
Operation
procedure for vacuum
drying
Due to
different construction
environment
,
two
kinds
of vacuum
drying
ways could
be
chosen
,
namely
ordinary vacuum
drying
and
special
vacuum
drying
.
3
.
1 Ordinary vacuum drying
1
.
When
conduct
first
vacuum
drying
,
connect pressure
gauge
to
the
infusing
mouth
of
gas
pipe
and
liquid
pipe
,
and
keep
vacuum
pump
running
for
1hour
(
vacuum
degree
of
vacuum
pump
shall
be
reached
-
755mmHg
).
2 If
the
vacuum
degree of vacuum
pump
could not reach
-
755mmHg
after
1
hour
of drying
,
it
indicates
that
there
is
moisture
or leakage
in
pipeline
system
and
need
to
go
on
with
drying for
half
an hour
.
3 If
the
vacuum
degree of vacuum
pump
still
could
not reach
-
755mmHg after 1
.
5 hours of drying
,
check
whether there
is
leakage
source
.
4 Leakage
test
:
After the
vacuum
degree
reaches
-
755mmHg
,
stop
vacuum
drying
and
keep
the
pressure
for
1
hour
.
If
the
indicator
of vacuum gauge
does
not
go
up
,
it is qualified
.
If
going
up
,
it indicates
that
there
is
moisture
or leak
source
.
3
.
2 Special vacuum
drying
The special vacuum
drying
method
shall
be
adopted
when
:
1
.
Finding
moisture
during
flushing
refrigerant
pipe
.
2
.
Conducting
construction
on
rainy day
,
because rain water
might
penetrated
into
pi peline
.
3
.
Construction
period
is
long
,
and
rain
water
might
penetrated
into
pipeline
.
4
.
Rain
water might penetrate
into
pipeline
during
construction
.
Procedures
of
special
vacuum
drying
are
as
follows
:
1
.
V acuum
drying
for
1
hour
.
2
.
V acuum damage
,
filling
nitrogen
to
reach
0
.
5Kgf
/
cm2
.
Because nitrogen
is
dry gas
,
vacuum
damage
could
achieve
the
effect
of
vacuum
drying
,
but this
method
could
not achieve
drying
thoroughly when
there
is
too
much
moisture
.
Therefore
,
special
attention
shall
be
drawn
to
prevent
the
entering
of
water
and
the
formation
of
condensate
water
.
3
.
V acuum
drying
again for half
an hour
.
If
the
pressure
reached
-
755mmHg
,
start
to pressure leakage
test
.
If it
can
not reached the
value
,
repeat vacuum damage and
vacuum drying
again
for
1
hour
.
4 Leakage
test
:
After the
vacuum
degree
reaches
-
755mmHg
,
stop
vacuum
drying
and
keep
the
pressure
for
1
hour
.
If
the
indicator
of vacuum gauge
does
not
go
up
,
it is qualified
.
If
going
up
,
it indicates
that
there
is
moisture
or leak source
.
