Great video.
If you want a measure what someone who didn’t know diddley learned about injectors here’s what I now think is going on.
Steam is injected into cool water, as no mention of a bleed was made the steam must be condensing within the water fast enough to keep the speed of the mix high enough to create a hydraulic ram effect.
Hot water or air bubbles screws up the ram.
Is there a reed or some periodic shut off that causes the ram to work?
The momentum of the water (hitting something?) overcomes the pressure of the boiler to let the water in.
As an engineer it seems pretty complicated. Did anyone ever try making a pump, something like a steam air compressor, that would simply use a steam piston to pump water in?

As I understand it from my time studying the GENERAL many years ago, that was more or less the way early locomotives got water into the boiler. The main disadvantage of it being that water could only be pumped in while the locomotive was in motion. Injectors took care of that problem, and when the GENERAL was restored to operation in the early 1960's an injector was added to supplement/back up the original pump system.

Nice video, John!