Vacuum pumps are part of one of the final processes in the repair process. After you’ve diagnosed and repaired any 
leaks or various other issues in the machine it’s time to recharge. Before recharging you desire to make sure the system is free from any unwanted gasses, air, or water. If these were to remain in the machine, it would turn the essential oil it runs on into sludge and leave behind damaging impurities.
The draw on a vacuum pump is usually broken down into its “CFM,” or Cubic Feet per Ac Vacuum Pump Minute. To estimate what your CFM needs, look at the tonnage of the systems you focus on. Take the square root of that number and you’ll get the approximate CFM you must have to work with that system. Typical home systems need 4-5 CFM, while industrial and rooftop systems generally need just as much as 6-8 CFM.