There is greater pressure in the water bottle than at the exhaust of the engine. That pressure differential causes the water to flow from the bottle through the system to the exhaust. The water gains energy in the heat exchanger, transports that heat to the engine where it gives up the heat by turning it into work (turning the propeller).I do not understand why the steam does not go backwards into the water bottle too.
Is the engine basically runing on the 100 PSI pressure of the water tank?
I went to B&W's welding school to weld their boiler tubes and welded their Boiliers for several years and also worked for Combustion Engineering on many, many jobs.I like the B&W Steam much better than Combustion Engineering but I have used both extensively.