Looking for a good picture or diagram of a hot water boiler and its components for training ...anyone?

we work on small boilers in apartment buildings(200,000 to 500,000 BTU)need a BIG pic or diagram of a boiler, PT gauge,low water cutoff, hi limit, stack switch, roll-out switch, pressure relief valve, gas valve, pressure reducing valve(auto-fill), RPZ valve(backflow preventer) and all shut off valves