THE OPERATION OF LIVE STEAM INJECTORS 

Years ago I drove/repaired a 11? Royal Scot constructed by a local guy in the 1960,s. Was a marvelous build with tons of power. How ever one was required to keep a small hammer on hand. This was to get the injector to start doing its job. I read all I could about injectors but no luck. Apparently the whole setup was sold to some on in the States ( I live in Canada) included was a CPR Hudson that I was unable get running due my employer not willing to fork out the cash. I really enjoy this channel.

Injectors are the bane of my life. I have a 4" Foster and the overflow has always dribbled, no matter if it's a new one, old one that's been pickled, and I have tried different sizes. Now I have a clear hose that returns the excess water back into the tender. There's no leaks in the supply pipe as it will pick up quickly, but I cry when I see others just work.

The principles behind these injectors are really not all that difficult. They are somewhat detailed, but very straightforward. The idea that Bernoulli recognized, is that the kinetic energy in a moving stream of fluid is equivalent to head pressure (potential energy) and these two forms of energy can be interconverted. Very basically, the injector works a lot like pushing a puddle of water up a hill with a nozzle on a garden hose. Where people get hung up is in thinking about the pressure of the boiler. Injectors do not work on pressure. They work on the velocity and density (>kinetic energy) of a precisely tuned water jet operating at approximately atmospheric pressure, and conversions between kinetic and potential energy. The first cone (nozzle) uses the potential energy of the steam pressure to produce a high velocity steam jet with high kinetic energy. The second cone (combiner) draws water into the steam jet, producing a high velocity water jet where optimally all of the steam has condensed, and all of the kinetic energy (and heat of vaporization) of the steam jet has transferred to the water jet. It is now a lot like the water jet that comes out of a pressure washer nozzle that makes a stream instead of a fan. When properly adjusted, there is no steam left in the water jet, and there is no excess water. This water jet is precisely directed into the third cone which is positioned and sized to just exactly catch the entire cross sectional area of the water jet, not more, not less, and converts the kinetic energy of the water jet into potential energy (pressure) of a slow velocity stream of high pressure water which is dependent only on the velocity and density of the water jet that it caught. It is not directly related to the pressure of the steam supplied to the first cone. Remember, this water jet is formed at atmospheric pressure, the pressure at the overflow port. This third cone works a lot like a Pitot tube on an airplane, where ram air velocity is sampled as pressure. The first two cones together function as an ejector (of the supply water) that has been precisely tuned for maximum density and velocity of the water stream, giving it maximum kinetic energy. This is why you have to adjust the water valve carefully. This is also why the cones have to be clean, so the water jet flows smoothly. If you provide too little water, there is still steam in the jet and the kinetic energy is less than maximum. If you provide too much water, the third cone cannot catch it all, and energy is wasted. If the injector body or the feed water is too warm, the steam in the jet will not completely condense, reducing the density of the water jet causing inefficient energy transfer. If there is an air leak in the water supply, the density of the water jet cannot be maximized because air is not condensable, and the injector won't work. Hope this helps.

Im new to the hobby and still getting to grips with injectors so I have found all your videos in bite sized chunks on the subject really useful. Be really great if you could cover vacuum brakes in similar detail👍

I think that you're right about the black art thing... I simply can't get my head around steam injectors, simply putting them in the category of 'magic'.

Not long ago when Keith was talking about another loco and it's steam injector I looked up steam injectors on Wikipedia It was then that a memory was activated of my science teacher explaining " entraining " to us and how it related to some simple laws of thermodynamics. It's a simple device and it made engines better and more economical to run, yet the man who invented it, Henri Guiffard made no money from it as his company claimed the patent for it. Typical isn't it? "I oil the engine and shovel the coal but get no credit, and if the engine jumps the track guess who catches hell?"

💯 Thanks again brother! -Drummer

I would like to be able to use the injector on my locomotive whilst on the move but cannot see the overflow. It almost looks as though the extention on the injector is detatchable but I think its soldered on. I could try threading the overflow 1/4 x 40 the pipe looks thick enough to take it and then I could attach an extention pipe. Have also looked for an elbow shaped piece of plastic which would push on but this has proved difficult.

I notice you use the same rolling roads that we set at Miniature Railway Workshop which is where I now work. Could you also try to explain the logic behind traction engine scales? Locomotives are easy because is governed by the track width, but I don't understand the traction engines.

Very informative. Keep up the good work.

Thank you for that, very informative

The part that I don't get is that the steam input for the injector is at boiler pressure but its pumping into the boiler. So I'm not sure how the steam flows since the input and output to the injector is at boiler pressure

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