Earl - I have no expertise in these matters, but Bruce's diagram made sense to me. If what you suggest is the case, what is the purpose of the elbow pipe located below the pump? It's in a logical location to function as Bruce suggested.
Also - presuming this was added post-manufacture, how was the water fed to the boiler originally?
Anyone - is there a reason why the air brake needed such a large tank? It's just a shade smaller in diameter than the boiler's horizontal section - and longer.
Charles