Vacuum Facts: When is the last time you changed your vacuum pump oil? If you had to scratch your head it has been way too long! The oil in your pump absorbs the moisture and non-condensable that you removed from the system. Only clean dry oil will allow your vacuum pump to achieve a deep vacuum while extending the life of the pump. The pump oil should be changed after every use while the oil is still hot. A micron gauge must be used to check pump efficiency regularly. A high-quality pump will incorporate a gas ballast that will help prevent moisture from condensing in the pump oil. Moisture in the pump oil will prevent proper evacuation. Make sure the pump you choose has a gas ballast, as most cheaper pumps don’t.
Bigger is not always better! The pump capacity has little to do with how fast a system can be evacuated. To select the proper pump, square the CFM rating. For a 3 CFM pump, 3X3 = 9, so it is good for up to 9 tons. A 5 CFM pump is good for 25 tons and a 7CFM 49 tons. To reduce evacuation time remove the Schrader cores with a vacuum Schrader core remover. Use a service manifold that has a 3/8 evacuation hose and evacuate from both low and high side.
Whether you run the pump for an hour or a day you can’t be assured of a dry system. Pulling and holding a 400-500 micron vacuum using a high-quality micron gauge like JB’s New DV-41 is the only way to be sure you have a clean, dry and leak free system. 30”hg is equal to 738,000 microns or 1” hg is equal to 24,600 microns so just how accurate is your manifolds compound gauge for measuring vacuum? POE oil is not very forgiving; do you really want to take a chance?