Re: We be injections (was AIR BRAKES 101.... was Re: RGS #20. Was: [HOn3] Division Point K-27 question)
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I cannot claim much knowledge on the subject, just the basics and a few details. Injectors came in three basic types: the familiar lifting injector placed high on the boiler, and less known non-lifting injector placed under the cab, which can powered by either full boiler pressure steam or exhaust steam.
Lifting injectors lift water from the tender or tanks by generating a partial vacuum using a steam jet. If the water or the injector is too hot, the water will boil and the injector cannot lift it. Internally the injector is a precise arrangement of concentric converging and diverging cones: A steam jet and venturi for drawing in water and accelerating it, a mixing cone where the steam is condensed, and a pressure cone where the jet's impact builds the pressure needed to force the water into the boiler. Don't ask me how or why it works - I'm just reporting on what I find in drawings. But if the feed water contains any suspended grit, or is unusually hard, abrasion or deposition that reshapes the cones will degrade the injector's performance, to possible failure.
With non-lifting injectors, the feed problem is the possibility of drowning the injector with too much water. They are also subject to the same degradation of the cones. The exhaust steam version required auxiliary steam from the boiler when the engine was not working, and perhaps on starting, making their construction and operation more complicated than full pressure injectors. These were a fairly late development, say late 1920s, and the only North American narrow gauge use that I am aware of was on the Uintah and NdeM Mallets, and the White Pass 70 & 71.
Probably the most common source of injector failure was operator error, due largely to the multiplicity of designs, each with their unique details and often idiosyncratic operating quirks.
On October 11, 2020 at 12:46 PM "Lee Gustafson via groups.io" <bagustaf@...> wrote: