Injector - The injector is perhaps the most arcane piece of plumbing on a steam tractor, and is subject to the most superstitions regarding its use.
    The basic idea is to use the venturi effect to enable a jet of steam to force fresh water into the boiler, thus replacing what is being consumed by the engine. Although the steam at the top of a boiler and the water at the bottom are under the same pressure (Pascal's law), when released to the atmosphere they have markedly different velocities, due to the lower density of the steam compared to the water. The injector condenses the steam back to water, but the molecules retain their former velocity. The velocity differential is enough to lift the feedwater out of the tank, mix with the "steam", and both then push through the check valves and into the boiler. The feedwater, being colder, helps the condensation process.
    Starting an injector, if all is in order, is as simple as opening the feedwater valve, and then the steam valve. The injector will blow steam out of the overflow for a few moments while the feedwater is drawn up the pipe or hose, then everything will balance and the overflow will cease and the injector will be putting water into the boiler. A correctly working injector usually vibrates the water within the pipe a bit, making a "singing" noise. Placing the injector low so that the injector is at or below tank water level, reducing or eliminating the need to lift the feedwater, would help ensure proper operation, but this was more commonly a railroad practice, not an agricultural practice. It is generally thought that fully opening the steam valve and throttling the water valve to control the injector was the best practice, as it would impart the greatest amount of heat to the makeup water, reducing its cooling effect on the boiler.
    Many engineers have bought into the notion that all injectors are unique individuals that must be handled a certain way to work at all, much like opening a safe, with the "combination" of one injector being unrelated to the "combination" of another. It may be true that the specifics of design, installation, and wear have some bearing on the exact efficiency of a given injector in a given situation, but to consider every injector as being possessed of an independent nature is not correct. The laws of physics are constants. Instead of learning an injector's secret sequence, you would be better off asking why an injector is failing to work when it should, and then fixing the underlying problem.
    Starting an injector when all is not in order is a different story. The most common problem is hot feedwater. If the feedwater does not cool the steam sufficiently to condense the flow, then the injector will not work correctly, if at all. The feedwater could be hot from being in the tank with the sun shining on it during a hot summer day, or it could be hot from proximity to the boiler, or from passing through pipes near the boiler. The common practice of locating the injector right next to the boiler aggravates the problem. The cures include cooling the tank water with fresh cold water, and pouring water over the injector to cool the injector body. Sometimes a few pieces of wood between the injector and the boiler can insulate it enough that it stays cool enough to function. Replumbing the injector so it's farther from the boiler is a more involved solution, but may be a good plan. Another cause of hot injectors are leaky check valves. A scored seat or a piece of grit in a check valve can allow boiler water and steam to burp back through the pipe to the injector, heating it and sometimes the feedwater too. Cleaning or regrinding the check valve, or adding a strainer/filter can be helpful. A few engineers have tried turning the check valve upside down, on the theory that grit will fall out easier.
    The second most common problem is a suction leak. If the feedwater line has an opening that allows air to be sucked into the line, it will be nearly impossible to lift feedwater any distance. Many engines use rubber hoses between the tanks and injectors, and these may be old enough to be have hardened and cracked, or they may not fit tightly enough on the pipe nipple leading to the injector. Renewing the hose, or putting a hose clamp on the end may help.
    The third most common problem is operator error, usually in the form of dry tanks. The injector will never successfully suck water from an empty tank, although most of us have tried at least once. Another common stumper is to forget to open the feedwater inlet valves on the boiler (most of us have tried that, too).
    Less likely is for the injector to be limed up. Some waters have a significant amount of dissolved lime that will deposit itself everywhere in the water spaces of the engine. In the injector, it can build up to the point that it changes the shape of the venturi jets or blocks passages inside the injector. The cure is to disassemble and soak the injector in an acid bath that will clean the lime off of the brass. Typically, muriatic acid is used for this purpose. Most hardware stores carry muriatic acid, a 20% hydrochloric acid solution. Read the safety instructions on the container (gloves and safety goggles are a plus), and using a plastic bucket, mix the muriatic with tapwater 10:1 to form a 2% solution, and place the injector parts in it (use enough liquid to completely cover the injector parts). Let the parts soak for a few minutes, then remove and rinse with fresh water and inspect to see if continued soaking is needed. Do not leave the parts in too long, as once the lime is absorbed, the hydrochloric acid is perfectly happy to attack the zinc in the brass, turning your solid brass injector into a porous copper one. Once things seem to be metal colored again, rinse thoroughly, reassemble the injector and reinstall.
    Occasionally the strainers on the tank ends of the feedwater hoses or pipes will become plugged, either from rust and corrosion, or crud from the bottom of the tank packed around them.
    After the above fixes have been tried, we enter the territory of serious head scratching. If you have steam, water, suction, sufficient cooling of the steam, and plumbing access to the boiler, the injector should work. If it doesn't, then you might be dealing with a severely worn venturi, an injector that isn't built to handle this particular pressure range, plumbing that's not routed correctly (I've seen the connections get swapped around by accident), or something more mysterious.
    The pressure range is one of the easier things to check. Penberthy injectors were commonly used by Case and other makes, and Penberthy is still in business today. Each injector was stamped with a code indicating the pipe size and pressure range the injector was built for, viewable here [Penberthy chart]. The erosion of worn jets can usually be seen by eye, once the injector is apart, but very few resources are available for figuring out how to reproduce them. The pipe connections (generally) should be as follows: Steam inlet at the top (vertical), water inlet mid level, and water outlet towards the bottom (both waters are usually horizontal connections). The overflow usually points straight down, and sometimes there's a drain cock on the very bottom.