Depressurising the air system?

hello, does anyone know how this is done manually and not through test book? Rave manual says it must be done through test book but Im sure there must be another way....?

Depends what you want to do, if changing an air spring or compressor, just pull the pipes off, thats all i do and never had any trouble.

If you need to take the air tank off then thats a different story.

I was looking at replacing the air filters and possibly later on replacing the airbag suspension units, would I need to depressurize the cylinder for any of these two? this is all new to me, and I cant seem to find any information on this..... thanks for the reply, ( Im used to springs this air system malarchy is confusing!!!! LMAO)