YORK INTERNATIONAL
26
FORM 160.54-O2(1102)
FORM 160.54-O2(1102)
27
YORK INTERNATIONAL
VACUUM DEHYDRATION
To obtain a sufficiently dry system, the following in-
structions have been assembled to provide an effective
method for evacuating and dehydrating a system in the
field. Although there are several methods of dehy-
drating a system, we are recommending the following,
as it produces one of the best results, and affords a
means of obtaining accurate readings as to the extent of
dehydration.
The equipment required to follow this method of de-
hydration consists of a wet bulb indicator or vacuum
gauge, a chart showing the relation between dew
point temperature and pressure in inches of mercury
(vacuum), (See Table 2) and a vacuum pump capable
of pumping a suitable vacuum on the system.
OPERATION
Dehydration of a refrigerant system can be obtained
by this method because the water present in the
system reacts much as a refrigerant would. By pull-
ing down the pressure in the system to a point where
its saturation temperature is considerably below that
of room temperature, heat will flow from the room
through the walls of the system and vaporize the wa-
ter, allowing a large percentage of it to be removed by
the vacuum pump. The length of time necessary for
the dehydration of a system is dependent on the size
or volume of the system, the capacity and efficiency
of the vacuum pump, the room temperature and the
quantity of water present in the system. By the use
of the vacuum indicator as suggested, the test tube
will be evacuated to the same pressure as the system,
and the distilled water will be maintained at the same
saturation temperature as any free water in the system,
and this temperature can be observed on the thermom-
eter.
If the system has been pressure tested and found to be
tight prior to evacuation, then the saturation tempera-
ture recordings should follow a curve similar to the
typical saturation curve shown as Fig. 12.
The temperature of the water in the test tube will drop
as the pressure decreases, until the boiling point is
reached, at which point the temperature will level off
and remain at this level until all of the water in the
shell is vaporized. When this final vaporization has
taken place the pressure and temperature will continue
to drop until eventually a temperature of 35°F (1.6°C)
or a pressure of 5 mm Hg. is reached.
When this point is reached, practically all of the air
has been evacuated from the system, but there is still
a small amount of moisture left. In order to provide
a medium for carrying this residual moisture to the
vacuum pump, nitrogen should be introduced into the
system to bring it to atmospheric pressure and the indi-
cator temperature will return to approximately ambient
temperature. Close off the system again, and start the
second evacuation.
The relatively small amount of moisture left will be
carried out through the vacuum pump and the tem-
perature or pressure shown by the indicator should
drop uniformly until it reaches a temperature of 35°F
(1.6°C) or a pressure of 5 mm Hg.
When the vacuum indicator registers this temperature
or pressure, it is a positive sign that the system is
evacuated and dehydrated to the recommended limit.
If this level cannot be reached, it is evident that there
is a leak somewhere in the system. Any leaks must be
corrected before the indicator can be pulled down to
35°F or 5 mm Hg. in the primary evacuation.
During the primary pulldown, keep a careful watch
on the wet bulb indicator temperature, and do not let
it fall below 35°F (1.6°C). If the temperature is al-
lowed to fall to 32°F (0°C), the water in the test tube
will freeze, and the result will be a faulty temperature
reading.
FIG. 12 –
SATURATION CURVE
LD00474
6
