To choose a suitable vacuum cleaner generator, you must consider the suction rate, vacuum level, evacuation time, air consumption, and operation of the vacuum generator. The maximum suction rate is defined as the maximum flow rate that the vacuum generator evacuates from the environment and is probably the most important consideration of them all. The vacuum level is typically given as a percentage which indicates at what pressure the vacuum is lower than the ambient pressure. The evacuation time is the time in seconds that is required to create the specified vacuum level, while the air consumption is a rating given in SCFM.