Refrigerant Charging Jake Quamme

Since refrigerant charging is typically much faster than evacuation, we often find excess charging capacity sitting right behind a bottleneck at the evacuation stage.  As a result, we frequently hear our customers ask what they can do to reduce their evacuation time.
There are several methods, each with its own advantages, drawbacks and strings attached.  The best answer must be tailored to your specific application.  The hard truth is however, that there is no magic evacuation machine (yet?).  It comes down to basic physical principles.  But fret not, there are things you can do!
One of the first things that many people turn to is a larger pump size.  Yes, this can decrease your evacuation time, but there is a major caveat here:  the maximum pumping speed (usually measured in CFM) is only relevant when there is still enough air in the system to fill that pipeline.  Imagine you’ve got a circuit with an internal volume of 5 cubic feet.  You currently use a 5cfm pump.  Why does it take significantly longer than 1 minute to fully evacuate the system?  Because life isn’t fair!  Furthermore, once you get down to lower micron levels, the remaining air molecules become further and further apart which means that the low pressure generated by the pump is less and less effective in “grabbing” them and pulling them out of the system. (More on this further down.) At this level, the size of your pump could be 100cfm or 5cfm, and your pumping speed will be almost identical. (this is, of course, comparing similarly constructed pumps.  Two-stage pumps perform better at lower micron levels than single-stage pumps).  A larger pump may evacuate faster, but only if you’ve got an internal volume that is quite a bit larger than the cfm speed of the pump so that it operates longer at full capacity.