On the subject of turbos, I did have a couple of photos, but not on the server.
First, a photo of my bus engine compartment when I purchased it. This may or may not be the factory configuration for a turbo, as I have the distinct feeling that this bus was fitted with a turbo after it had been in service for a while:
The exhaust enters the turbo expressor at the top of the assembly and exits the rear, passing through an exhaust brake butterfly plate operated via pneumatics.
Intake air is drawn from the air cleaner into the compressor side of the turbo and expelled into the intake manifold of the engine (on the bottom).
Since I have "nothing leaves stock" disease, and because I wanted to maximize under-frame area for mounting tanks, batteries and such, I ditched the original big box air filter and fitted the engine with a disposable cartridge-type filter, fabricating a cradle for it between the engine and the body sheet metal. In order to make the filter last as long as possible, the cartridge filter is fed through a custom fabricated pre-filter that uses throw-away blue polyester filter media which is impregnated with an oily substance to trap particles (that's the white square to the right of the photo). It gets cruddy pretty fast, but at less than $.50 a filter change, I could replace it daily and still be ahead.
As for your brakes, my coach has had significant upgrades to the air brake system, but the principles are the same. There are three air reservoirs on the bus, primary, secondary, and emergency. The air comressor supplies air to the primary system, which runs all of the air-operated accessories,
except the brakes (curb door actuator, windshield wipers, inter-axle differential lockout, exhaust brake, etc.)
There is a check valve which allows air to enter the secondary reservoir, but not return. This secondary system runs the braking system. If you lose pressure in the primary system, you have a few brake application's worth of air pressure left in the secondary reservoir.
If you lose pressure in the secondary system, the pressure holding the wheel brakes
released goes away, and the spring brakes built into each wheel assembly take over, locking up the rear wheels (rear
only, you don't want the front wheels to lock up if the compressor fails!)
From the secondary system, there is another check valve to the emergency system reservoir. The only purpose of the emergency system is to allow the brakes to be released once, and only for a short time. If the bus runs out of air and the wheels lock up in the middle of a busy intersection, or sitting across railroad tracks, the emergency system may allow the bus to be moved to safety. This is probably what the second knob is for.
If you are going to own a bus with air brakes (and they are the only type to have on a rig that sits a lot), I suggest you learn more about them -and- how to check and adjust them properly. Fortunately, I happen to have a cure for this lack of knowledge:
Bendix Air Brake Handbook (in PDF format, please save to your hard drive to keep my bandwidth low)
Bendix Slack Adjusters Handbook Adjusting air brakes isn't hard, but ~very~ important, they go from working dandy to not being there at all with NO noticeable pedal feeling change.
