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
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
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
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
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.