Dehydration; Table 28 - System Pressures - York YVAA Installation Operation & Maintenance

SECTION 9 - MAINTENANCE

Table 28 - System pressures

Gauge
Inches of mercury
(Hg) below one
standard atmosphere
0 in.
10.240 in.
22.050 in.
25.980 in.
27.950 in.
28.940 in.
29.530 in.
29.670 in.
29.720 in.
29.842 in.
29.882 in.
29.901 in.
29.917 in.
29.919 in.
29.9206 in.
29.921 in.
Note:
• One standard atmosphere = 14.696 psia = 760 mm Hg absolute pressure at 32°F = 29.921 in. Hg absolute at 32°F
• psig = pound per square inch gauge pressure = pressure above atmosphere
• psia = pound per square inch absolute pressure = sum of gauge plus atmospheric pressure
• Shell volume = L*π * r2= (Length in feet)*( 3.1416)*(radius squared) = cubic feet
To keep the units consistent, round the length and radius to the nearest tenth of a foot.
• μm = Micron

Dehydration

To make sure that there is confidence in the vacuum
decay related to moisture boiling off, only perform the
dehydration process after the system has been thor-
oughly leak checked. The dehydration process is only
needed if the following occurs:
1. The nitrogen holding charge on shipments has
been lost.
2. The system has been open to the atmosphere for
any length of time.
3. Tube leaks have introduced moisture to the refrig-
erant circuit.
4. Indications of moisture contamination have ap-
peared in any of the sight glasses Dehydration of
166
Absolute
psia Millimeters of
mercury (Hg)
14.6960 760.00
9.6290 500.00
3.8650 200.00
1.9350 100.00
0.9680 50.00
0.4810 25.00
0.1920 10.00
0.1220 6.30
0.0990 5.00
0.0390 2.00
0.0190 1.00
0.0100 0.50
0.0020 0.10
0.0010 0.05
0.0002 0.01
0
Microns
760,000
500,000
200,000
100,000
50,000
25,000
10,000
6,300
5,000
2,000
1,000
500
100
50
10
0 0
a refrigerant system can be obtained by the evacu-
ation method because the water present in the
system reacts much as a refrigerant would. How-
ever, the vacuum pressure in the system cannot
always be pulled down to a point where its satura-
tion temperature is considerably below that of the
equipment room temperature due to low ambient
room conditions and other factors. As a result, you
might need to use an external heat source or flow
warm water through at least one vessel to raise
the vessel internal temperature. This ensures that
heat flows into the system and helps to vaporize
the water, so that a large percentage of it can be
removed by the vacuum pump.
The length of time necessary for the dehydration of a
system depends on the size or volume of the system,
Form 201.47-ICOM1
Issue date: 17/11/2022
Boiling temperatures
of water, ⁰F
212
192
151
124
101
78
52
40
35
15
1
–11
–38
–50
–70
JOHNSON CONTROLS