400P-Automatic is VIAIR’s first Automatic shut-off function portable compressor. This 33% duty cycle unit is capable of pressures up to 150 PSI and can be operated for up to 40 minutes at a time before needing to be rested (at up to 40 PSI). The 400P-Automatic comes with a close-ended gas station-style air gun for added convenience.Portable compressors with automatic shutoff come into play when moving from tire to tire, and when checking tire pressure in the middle of a tire fill. A typical portable compressor must be turned off between tire fills, and anytime you want to check tire pressure. If you aren’t near the compressor, this can turn into running laps back and forth to the portable compressor to turn the unit on and off. Automatic portables do not work in this fashion and will save you time & effort to get tires inflated quickly.