Too much air pressure on Bedford Library Bus!
 

I've got a 1982 Bedford Library bus with Bedford 330 diesel engine 3.2.

The air pressure always used to run at around 7 to 8 bars but recently its been soaring up to 10 bars. There's a new sound which seems to be a safety pressure release which kicks in every few seconds while I'm driving.
Does anyone know if its dangerous to be maxed out on air pressure like this? Could it be caused by a fault in the door mechanism because I'm also not able to close the side door when the engine's running and so have to brace it with a bar while I'm driving.

I'd be so glad to hear any advice/ideas.

Clive.