24431
Rev. A
10/12
http: www.networketi.com
Environmental Technology, Inc.
11 of 94
Automatic Air Dehydrator
ADH
®
SIROCCO™
Instruction Manual
DESCRIPTION AND THEORY OF OPERATION
A detailed product description and theory of operation for the ADH Sirocco
automatic air dehydrator are presented below.
FUNCTION
Unpressurized transmission lines allow the entry of moist ambient air through
leaking seals and cracks. When the line passes from one environment to
another (such as entering a shelter from the antenna outside) or when there is a
change in existing environmental conditions (such as a weather front or nightfall)
the pressure and/or temperature changes in the air will result in the collection of
water inside the line. This is normally the result of the ambient temperature
dropping below the dew point. Water in transmission lines causes corrosion,
voltage arcing, and increased VSWR, all of which reduce system performance.
The ADH Sirocco automatic air dehydrator prevents the accumulation of moisture
in transmission lines by maintaining the pressure and dew point of the air inside
the line. Supplying low pressure dry air, the ADH Sirocco keeps waveguides, air-
dielectric coaxial cable and related components used in earth station and
terrestrial UHF and microwave communication systems dry.
PRINCIPAL CONSIDERATIONS
The ADH Sirocco automatic air dehydrator works best supplying dry air in a
flowing system, where the dehydrator completely replaces the air on a regular
basis. Consequently, the equipment being supplied dry air should have a bleed
system. For a waveguide, this is best accomplished by slightly opening a purge
valve at the window end of the system. Installing a pressure relief valve,
purposely set higher than the High Limit Target Pressure, will allow the solar
pressure gain to bleed off. This will provide for greater system stability and
repetitive daily performance and results. Likewise, air dielectric coaxial cable
should be equipped with a valve at the far end which can be set to allow a small
continuous bleed. Many systems will have sufficient normal leakage that such
actions might not be necessary. For optimal performance and life expectancy of
the dehydrator, a duty cycle between 1% and 10% is recommended.
The ADH Sirocco has check valves in the air path and a pressure relief valve. A
tightly sealed system may experience a pressure increase with a rise in ambient
temperature. The ADH Sirocco will relieve such build-up should it reach 8 psig
(552mbar) but it is advised the ADH Sirocco not be used as the only means of
overpressure protection.
