106 South Elm Street, Newkirk, Oklahoma 74647
During the early part of the 20th Century, the piston steam
engine was in almost universal use driving the machinery in
factories and the generators in electric light plants; Corliss
engines in the larger, ‘Automatics’ in the smaller
plants.
The operating engineers who attended the engines were generally
required to hold an operator’s license. To obtain it he would
need to have at least an elementary knowledge of a device called
the steam engine indicator.
The indicator is not a very complicated instrument. James Watt
invented it. It is just about impossible to set the valves on a
Corliss engine without an indicator and it is a great help in
getting the valve on an ‘automatic’ especially a piston
valve.
The indicator shows the engineer how the steam is acting in the
cylinder: the ‘valve events’; admission; cut-off; and
release on the power stroke and back pressure and compression on
the return. Any mis adjustment of the valve gear and leakage will
show. In fact, the indicator card shows the engineer the same
things that a cardiogram shows your doctor. The horsepower being
developed can be calculated.
An indicator is especially needed in adjusting the reversing
gears on traction engines and locomotives. The builders of traction
engines needed them very badly but some surely didn’t use
them.
The writer operated a sawmill at Harrison, Arkansas, until a few
years ago. It was driven by a SKINNER steam engine with cylinder
diameter 14 inch, stroke 15 inch and with Shepard automatic valve
gear with ‘inertia’ governor.
I had been using two Case traction engines to pull the mill but
it got too big for them, so I set them aside to play with and
acquired the larger engine.
For this more ‘sophisticated’ valve gear, I needed an
indicator, and had the good luck to obtain a fine instrument that
had never been used and had been kept in perfect condition. The
trouble was that it had been made for use on large engines and the
reducing motion, or ‘detente’ as it is sometimes called
could only be used on from 36 down to 18-inch stroke. This caused
me to have to make a reducing motion. The one I made can be used on
15 down to 10-inch.
If any reader has ever had actual experience with an indicator,
I would be very glad to exchange cards, especially cards taken on a
traction engine. I would especially like to get some of the younger
steam engine lovers interested.
I strongly maintain that it is not possible to really know the
steam engine unless you know the indicator.
