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Rapid dehydration can accomplish the removal of moisture and in a fraction of the time traditional techniques require by maintaining the pressure during dehydration at 6000 microns or about 37 degrees.
The process provides a means of “sweeping” the system with a dry gas that promotes the movement of moisture while maintaining an atmosphere that will vaporize water.
Required components: Vacuum pump, Rota-meter with needle control valve scaled to about 10 SCFM, source of nitrogen capable of 1~1.5% by volume of the pump, 6 cfm pump/~.06-.09 cfm of N2, 300 cfm pump/ 3-5 cfm, and an electronic vacuum meter of good quality. See below:
CAUTION: ALWAYS USE AN APPROVED NITROGEN REGULATOR, A NITROGEN BOTTLE IS AT 3000 PSI!
The regulator pressure must be set at the inlet design pressure determined by the Rota-meter, which can be found at the Dwyer website.
Installation of the components: There is little criticality to the orientation of the devices but placing the nitrogen injection as far from the pump nozzle produces better results.
Find a “neutral” point to attach the electronic vacuum gauge. Look for a port that is about half way in between the meter and pump connection. The preferred spot should also be low traffic and safe for the electronics in the meter. Avoid low points also, if water or oil gets into your vacuum meter it may be finished for good! I also suggest using a cold trap and filter to protect your vacuum pump from destruction.
1. Pull an initial vacuum on the system until the electronic vacuum gauge reading is essentially stable. This reading should be somewhere below 5000 microns. If the pump is suitably sized for the system, the approximate time is less than an hour. If the system will not achieve a vacuum below 5000 in this amount of time, the pump may be too small, or faulty, or a leak still exists.
2. After reaching a stable operating point, set the flow of the Rota-Meter to about 1% of the volume flow of the pump. Monitor the vacuum gauge until the reading is stable. Adjust the nitrogen flow to establish an environment of ~6000 -8000 microns.
3. For general dehydration the system should remain stable and dehydration will be complete when the gauge ceases to drop. Constant fluctuation and necessary adjustments to the nitrogen indicate extreme quantities of water and/or leaks. The required dehydration will be two to three times longer. Constant monitoring of the system will be the only way to determine termination of the dehydration. If the oil mist ceases to purge from the pump exhaust, it is a sign that the process is very near complete.
4. Repeat the pull-down in step 1 and compare it to the chart below. If the reading maintains a steady trend for one hour below the line in the chart, the system is dry.
If the vacuum readings over time increase sharply, there is a leak, if they trend up slowly or cross the line, it is water in the system.
Below is a vacuum conversion chart.
I worked for over thirty years in the HVACR industry. I have designed, installed, serviced, and trouble shot units of various types throughout the years. The posts here are information based on that experience, I hope you find them useful. If you have a different experience, please comment.