you add the empty weight of the recovery cylinder to the 80% for your total. So, if the tank weighs 17 lbs. empty and you can only put 24 lbs. in the tank to reach your maximum capacity your total weight when the tanks is at 80% will be 41 lbs.
Try to never exceed this as many
HVAC supply house that trade out full cylinders for empty cylinders will not take them if they are over 80%.
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