When the machine works, it works well. However, it looks like there is some kind of check valve in there that prevents it from starting again after you inflate a tire. If you flick the power button a few times, it will start up again. This is very annoying. I sent the unit back thinking it was just one, but that also happens with exchanges. To get around this annoying problem, switch on the device while it is disconnected and then screw it to the bus. Disappointed with this brand, do not recommend.