Oh man that is fantastic info to have! If I can find one with a bad pump engine that would be an excellent starting pointSay, I looked at monotube flash steam boiler plan posted above. That is exactly how a hot high pressure washer is built. Mine does 4000 psi. Its got everything done for you, just remove the gas engine and pump. Get a feed water pump and you are good to go.
Start shopping Craig's list for an old broke one.
Well that is handy, I will have to check that. I know Washington has a law on hobby boilers that was reduced in scope a couple years ago but i havent found a definitive list of the limitations. Need to find someone from the area with the regulations book or something. The websites for WA are dang near useless 30+ pages just explaining who the board members are and the fines for non compliance but I cant find the actual regulations yetA possible advantage of monotube boilers is they are nearly always exempt from state laws governing the testing ,maintenance ,operation and qualification of tube boilers.......however most jurisdictions do have a "model boiler" code ,which generally means you can build a tube boiler to say 12" or 14" shell dia,and be within the model code.