Quick question for you about my truck a k reg scanni 93m, on the dashboard underneath the engine stop knob theres what looks to be like a valve similar to a car tyre valve any idea what its for ■■? Ive been prodding it with a screwdriver but it doesnt seem to do anything 
simon
It is for an airline, you can attach one of those curly airline dust blower things to it and blow the dust from one side of the cab to the other. 
im not sure but it sounds like the choke. if i am right then rotate it to adjust the idling speed of the truck
Scanny77 the choke is on the righthand side of the engine stop so i dont think its that 
Coffee it defo looks like a tyre valve so i think you could be right cheers
many thanks
simon
Ps tomorrow i will investigate further (bigger screwdriver) 
Just push in the centre pin, same as you would to let a tyre down and you should hear and feel air coming out.
sorry mate. its been ages since i last drove one 
simon usually scanias have a piece of tube with a valve on each end( like the one you blow tour tyres up with) in the tool kit ,it allows you to charge the handbrake system with air from the front tyre to allow you to relaese the hand brake, if your engine is dead and there is no air in the system, you can also use it as coffee said to blow dust around the cab
ditto malcn
but i wouldnt prod it too much cos when they leak its one of the MOST annoying sounds 
you will ever drive with ( apart from radio 1 )
the constant hiss is like having our lass in the cab