How does the compressor work ?
The air horns are blown by a FIAMM compressor (blue box that can be seen on the left hand side of the engine). Inside the compressor sits a "rotary vane compressor system". Here is how it works :
Source: Diverse

Compressor

This type is a "sealed for life". You must oil the inside of the box regularly using the air port or a dedicated port. A dry compressor will fail with age, the vanes will worn out.
Source: Diverse