GOSSIP FROM THE BACK SHOP

article image

I remember when once my morning trek to work was halted as I
heard the loud talking of a steam engine down in Hanson’s shop.
While he had a water brake set up for testing, it had never been in
operation while I had been around. This apparatus functions like a
Prony brake, but instead of using a brake band around the large
drum to tilt the scale when the engine is loaded up, a perforated
disk turns within a close-fitting housing through which water is
circulated. This makes control much easier with no tendency to bind
up. My old friend and master mechanic had just set the
double-ported valve on Walsh’s 10 horsepower Russell the night
before, and was running off some indicator cards to check the
overall balance of the engine.

‘Do all double-ported valves make that much racket under a
good load?’ I inquired of Mel while the noise from the stack
under the smoke jack in the shop sounded like an entire tribe of
African natives beating on large drums. ‘Well, quite
likely,’ he shouted back to me, ‘but the double-porting has
little or nothing to do with the snort of the exhaust, because the
extra valve passage is always under inlet steam and never sees the
exhaust port. It just lets the steam into the cylinder quicker at
the beginning of the stroke.’ Gee, come to think of it, the old
boy was right, and this point had never occurred to me before.

As his assistant let off on the water circulation and the engine
coasted along more quietly for a few minutes, Mel replaced the
indicator cards which he had just recorded and after moving the
reverse lever from its present position near center to that at full
quadrant, called to Manfred, ‘Alright, Manny, let’s have
the same amount of water again.’ I noticed that under these
conditions the old girl seemed to bark a bit louder than before,
although doing the same amount of work. At the end of this short
run, when Mel removed the indicator card with its traces for both
ends of the cylinder, I felt again the urge to seek a little more
knowledge. ‘Well, I know you are not studying X-ray pictures,
but what can you see there?’ I asked. While Manny shut the.
engine down, I trailed Mel over to the desk top on his work bench,
where he pulled a planimeter out of its cubbyhole and told me that
he was measuring the work load of each end of the cylinder, from
which he would calculate the cylinder horsepower. When he had
finished his figuring, he turned to me and said, ‘Now this may
be of interest to you. Notice that we have called for the same
given amount of work to be performed under hookup as under full
quadrant, and as closely verified by these diagrams. But with
hookup at about 40 percent the governor was riding low and running
full steam pressure to the chest, while consequently releasing it
to the atmosphere at a lower pressure than was possible under
maximum cutoff where the governor was throttling the steam to about
70 percent of full pressure under the same load.’ ‘I
don’t get what you are driving at,’ I puzzled, at this
point really wallowing down in my ignorance. ‘ If you would
quit wearing that dumphoozled Derby hat on your noggin,’ he
began razzing me, ‘you would remember that paper discussion we
had some time ago when I explained to you that, according to the
Rankin cycle, which describes what goes on in a steam cylinder, the
efficiency of a reciprocating steam engine is dependent upon
amongst other things, the ratio of the steam pressure at admission
to that at which release occurs.’ As my face reddened up a bit,
I had to admit he had me dead to rights there, and now I began to
see that under this principle an engine would run more efficiently
if it could be hooked up a bit. If many of you fellows to whom I am
telling this story are further interested, I will ask old Mel to
let us borrow those cards for publication.

Farm Collector Magazine
Farm Collector Magazine
Dedicated to the Preservation of Vintage Farm Equipment