GOSSIP FROM THE BACK SHOP

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By FRANK J BURRIS

35640 Avenue F Yucaipa, Calif.

This incident involves a rather unexpected happening in the
course of engineering, in which I, as an innocent bystander but
nevertheless interested, was to witness what at first hand might be
considered as backward progress. But I was reminded that not
everything that turns up in mechanical development is necessarily a
great stride ahead. At least as we look back on some of these
events today, we dislike thinking that some of these diesel and
combine outfits are anything but the works of the devil. But what I
am about to relate happened many years ago so my yarn may be viewed
in the understanding of things as we knew them then, -or at any
rate thought we did.

Upon this particular occasion I stopped by the doorway of old
Mel’s shop and was interested upon seeing Manfred, his
right-hand assistant, clearing the heavy wooden packing crate off
from a new simple cylinder and valve assembly which the freight man
had just delivered that morning. Along the roadway side entrance to
the shop was Harold Ferguson’s 25 horsepower Case with the
Wolff setup about half disassembled. ‘What is going on here,
anyhow?’ I inquired as the nice new cylinder casting burst into
full view. ‘Well, it looks like we aren’t going compound
any more with this old kettle,’ replied Manfred. Mel was just
finishing turning down an old salvage piston to fit the new bore,
and as his lathe came to a stop he shut down the old chugging gas
engine which powered the line shaft for all the heavy shop tools,
and chimed in, ‘Yes, Harold can’t work this steamer over
half capacity on that 34-inch separator. For the last two years he
is getting about as much economy out of his coal wagon as we are
out of turning these line shafts all the time; but someday we are
going to get some of these new-fangled individual electric motors
on this machinery and get connected up to the power line in this
town, like the newspaper did here a few months ago.’

‘But what has all this to do with this boiler?’ I
interjected, failing to see what electric motors had to do with a
compound traction engine only four years in the field.
‘Hmmm,’ replied Mel, ‘you must not have read that
Swingles’ Handbook I loaned you last winter. Somewhere along
about chapter six I recall that it mentions that under light loads
a compound engine will tend to waste fuel instead of conserve
it.’ ‘Gee whiz,’ I came back, ‘Steam is steam,
isn’t it?’ ‘Yes,’ said Mel, ‘but it all depends
upon what you do with it. Now, there is what is called a
closed-expansion loop between the high and low pressure cylinders,
where the exhaust steam from the high pressure end has a chance to
expand about an additional two-hundred percent against the low
pressure piston. But if the high pressure exhaust is down around 40
pounds pressure, there is a good chance that this pressure will
drop to atmospheric at about half-stroke. From there on to the end
a slight vacuum may be created; or at least there will not be
enough work performed in this loop to even run the engine alone
over this portion of the stroke. Now even this is not too much of
consequence in that old cross-compound standing out in the back
lot. But the deficiency is multiplied in the case of this Wolff job
because in this type of tandem connection there results too long a
path in the port passages from the single valve to the
high-pressure cylinder ends. This particular volume is about twenty
percent of that of the high-pressure cylinder. So when the single
valve opens to allow a full cylinder of steam, if we are working
the old girl properly, to pass on to the low pressure cylinder the
first thing this steam sees is a twenty-percent reduction in
pressure just filling up the long port passage. There is no inter
stage receiver, and the port had just finished exhausting the low
pressure steam, so all this work is lost. And if the old girl is
working light, the sin alone is compounded.

‘Golly,’ I budged in, ‘it looks like we should have
independent high and low pressure valves, with short steam passages
as possible, and a variable cutoff on the high-pressure cylinder
with a fixed cutoff on the low end,’ ‘You stick around
awhile,’ replied Mel,, ‘and I will put you to work helping
Manfred around here. Yes, this is the cheapest and simplest way to
get some compounding, but the Winnipeg tests last year showed that
you are doing a bit of good thinking. The economy of this type of
compound is only marginal at full load, and is hardly worth the
bother and fuss on medium and lighter work. Harold will get plenty
of good work out of this animal when we get her reassembled and all
tuned up. I think he will give you these old cylinders for that
drag weight you were looking for last week.’

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