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that is the inside pressure never fails below the
outside pressure, which ensures that high-moisture air cannot
enter the transmission line. Andrew automatic dehydrators are used to reduce the moisture content (and, therefore, the dew point) of air and maintain a pressure greater than atmospheric pressure. For transmission lines with typical leakage rates, the dehydrator should normally run once every 24 hours for no more than 72 minutes and no less than 10 minutes. Figure 4 is a simplified diagram of dehydrator operation. The purge-gas-stripping method of regeneration is used, where moisture is removed from the air at high pressure and returned to the atmospheric at low pressure. This is illustrated in Figure 5. In operation, the pressure sensitive switch closes whenever the transmission line pressure falls below 3 psi (21 kPa). |
This action applies power to the compressor motor,
the solenoid timing motor, and the purging cylinder solenoid valve.
The compressor draws air through a filter in both air intake assemblies, compresses it, and feeds it to the manifold for distribution to two solenoid valves. The air is then passed through both dryer cylinders and to the back pressure regulator valve. When the drying cylinder reaches a predetermined pressure, the regulator valve opens and connects the dehydrator output to the transmission line. Each dryer cylinder contains a molecular sieve type desiccant that absorbs (sucks in) moisture from the air passing through it. The moisture clings to the desiccant until the pressure is reduced to a value that causes the desiccant to expel the moisture. A stream of dry air is diverted through the cylinder and carries the expelled |
