6
PC=corrected final pressure, psig
PR=final pressure as read, psig
T1=beginning temperature, degrees F
T2=final temperature, degrees F
Note: A rule of thumb is that the final pressure should not be less than half the
initial pressure after twenty-four hours.
6. If the system looses pressure at an unacceptably high rate, re-pressurize.
7. Leave the gas/air supply on and find the leak(s) using a “leak detector” or
bubble soap.
Should it be necessary to identify a leak, use non-ammonia based leak detection
soap, such as Snoop, by Swagelok. If unavailable use a simple mixture of dish
detergent and water. Ammonia and ammonia-based chemicals are extremely
incompatible with brass and brass is one of the main components in
transmission line and antenna systems. Ammonia makes the brass more
susceptible to stress-corrosion cracking.
8. Correct any leaks that are found.
9. Repeat steps 2 thru 5.
D. Purging System
The transmission line and the antenna system should be purged prior to applying
power.
1. Purge by pressurizing the antenna array to about 10 psi (70 kPa) with
compressed dehydrated air or cylinder nitrogen
2. Loosen the connection between the transmission line and input section to power
divider just enough to allow an air leak.
3. Purge using table below.
Note: Usually allow three volume changes of dry gas/air for a system. See
table below for approximate volumes inside various coax sizes.
VOLUME OF COAX PER
1000 FEET OF LENGTH
Diameter Volume
1-5/8” 13 cu. ft.
3-1/8” 50 cu. ft.
4-1/16” 90 cu. ft.
6-1/8” 200 cu. ft.
One full nitrogen cylinder, size K, contains about 240 cubic feet of gas.
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