Abstract: The invention relates to an apparatus for applying multi-component coating compositions comprising at least two dosing devices, an air-assisted spray gun, and a controlling device, each dosing device comprising a supply container comprising one component of the multi-component coating composition, a motoring device, and a metering device, the supply container being connected to the metering device, the metering device being connected to the motoring device and to the air-assisted spray gun, the connecting line between at least one metering device and the air-assisted spray gun being fitted with a pressure transducer for measuring a decrease in pressure in the connecting line, the pressure transducer being connected to the controlling device, and the controlling device being connected to the motoring devices, the controlling device capable of comparing the decrease in pressure in the connecting line with a set value, for starting up the motoring devices, and controlling the power of the motoring devices to kee