106 South Elm Street, Newkirk, Oklahoma 74647
Most all of the men who play with steam engines know something
about the ‘Angularity of the Connecting Rod;’ but you
seldom hear the angularity of the eccentric rod mentioned.
Any connecting rod on an engine of any kind; a pitman on a
mowing machine; a pump; any device on which one end of a rod is
carried in a circle while the other is attached to a piston that
moves in a straight line, will have this same peculiarity of
movement. An eccentric, which is a modified crank, will cause a
valve to move in the same manner. A piston will at the instant of
‘dead center’ have no movement at all; but will be moving
at about 3-1/7 times the average speed at a point near, but not
exactly, at the center of the stroke. The writer owns an engine
with a 9-inch diameter piston and 10-inch stroke with connecting
rod 32′ long. When the crank pin is at the 90° point or, as
some call it, ‘the quarter,’ top or bottom, the piston will
be about 7/16′ past the mid-point of the stroke on the end
nearest to the crank. This means that there is about 7/8′ more
steam in the ‘head-end’ of the cylinder. This would result
in having about 10% more power in the ‘head-end’ of the
cylinder if some means of compensation is not provided.
In the most simple type of stationary engine, the angularity of
the eccentric rod serves to increase the time that the steam is on
the ‘head’ end; however, millions of feet of lumber were
sawn and millions of bushels of grain were threshed with valve
gears of this type. The exhaust from the head end was louder than
from the crank end; but that did not worry the operators much.
These engines were simple to adjust and repair, so any smart farm
hand could run them.
On the Stephenson reversing gear which was used on the first
successful locomotives, the later cut-off on the head end could be
corrected by using the indirect motion rocker arm to move the
valve. This causes the angularity of the eccentric rods to work in
opposition to that of the connecting rod, and serves to equalize
the power in the cylinder. Most of the earlier traction engines
used the Stephenson or, as it is sometimes called ‘Link
Reverse’, as it was difficult to design a traction engine with
an indirect motion rocker arm. They had more power in the head end.
Some of them had inside admission piston valves which equalizes the
cut-off.
A more important fault in the action of these eccentric gears is
that the opening and closing of the valve occurs in the slow part
of the valve motion. Early in the steam engine era engineers
learned they could get more power and efficiency if they had full
pressure at the beginning of the stroke.
During the latter half of the 19th century the steam engine was
the most important machine in existence and the best brains in the
world were occupied with trying to improve it. Dozens of valve
gears were patented. Some were only devices that would make the
engine run in the other direction, but some would give almost
perfect distribution of steam. Around the turn of the century a
type of gear called the ‘radical’ came into use on most
traction engines. These open the ports very quickly just before the
beginning of the stroke, then dwell for an instant and close
quickly. Some of the earlier models could not be adjusted for
exactly lead and cutoff points, but several of them were improved
until the lead remains constant while the reverse lever is moved
from one corner of the quadrant to the other. The writer owns an
engine built in 1915 that can be startedidle of course in either
direction then, the reverse lever brought slowly to the center
notch and it will continue to run. This engine, while running with
the lever in the center, is running on only the ‘lead’
opening, which is about one thirty-secondth of an inch. To perform
this way a valve gear must be perfectly adjusted and, of course,
designed right in the first place. I have handled two other engines
that would perform this way.
Now a few words about locomotives: the corresponding parts are
called different names from those on traction engines. Instead of
‘connecting rods’ they call it the ‘main rod’ but,
it has angularity. With a main rod 84′ long and stroke 28′
the piston will be a little less than one and three-sixteenth
inches closer to the axle end of the cylinder than to the head end
when the main crank-pin is at the quarter (or 90°) point, either
top or bottom. This will add up to nearly two and three-eights
inches, which would mean that there is about 9% more power on the
head end.
There is a very important difference in the way a valve gear on
a locomotive is constructed. Due to the action of the springs, the
frame has considerable movement up and down on the axle bearings.
For this reason all eccentric rods, or any part that imparts motion
to the valve, must move in a horizontal direction.
Practically all the locomotives built after 1900 were equipped
with the Waalsheart outside connected or, as some call it
‘monkey motion’ or a little later the Baker-Pilliod came on
the scene. The Baker-Pilliod was possibly the most perfect of any
of the valve gears. Both of these gears open the ports quickly as
the crank passes dead center, dwells for a split second then, due
to the motion of the ‘lap and lever’ or, as some called it
the ‘intervening bar,’ closes quickly for cut-off. Near the
end of the stroke the valve is moving fast and gives a quick
release so there is little back pressure. Engines equipped with
these gears could move heavy trains and saved steam by utilizing
expansion.
An old locomotive machinist allowed me to make copies of
indicator cards that were made by the Baker-Pilliod Company when
they were demonstrating their valve gear, trying to sell it to the
Chicago and Great Western Railroad in 1909. There are four of these
cards. The date was May 11, 1909. The first was made 4:30 p.m.,
location: Mile Post 171 Throttle Fullreverse lever in the 7th notch
from centersteam pressure 190RPM 240, MPH 48. Spring 100. (This
means that one inch in the height of the card equals 100 pounds of
pressure.) This card was not ‘worked’ so the horsepower is
not known. The cutoff was occurring at about 10% of the stroke. The
next card was made at 5:00 p.m.location: Mile Post 154-153;
throttle full; reverse lever in the 10th notch from center, steam
pressure 200, RPM 160, MPH 32. This card was worked. This means it
was calculated to show horsepower. The head end shows mean
effective pressure82.4. The crank end 82.1. The indicated
horsepower in the head end271.5. The indicated horsepower in the
crank end 252.7.
The third card was made at 5:11 p.m.Mile Post 149throttle
full-reverse lever in 11th notch from centersteam pressure 200MPH
40. This card was not worked. Horsepower not known.
The fourth card was made at 5:40 p.m. Location: Mile Post
134-133 throttle fullreverse lever in 12th notch from centersteam
pressure 190RPM 180, MPH 36. Head end mean pressure 85.5. Crank end
mean pressure 84.7. Indicated horse-power in head end 316.8.
Indicated horsepower in crank end 304.9. It may be noted there is
less indicated horsepower in the grank end than, in the head. The
area bf the piston rod is subtracted.
These cards all show almost perfect distribution of the steam.
At the beginning of the stroke, the pressure was very close to that
of the boiler. Cut-off was occurring at about 10% on the card with
the lever in the 7th notch and about 35% on the card with the lever
in the 12th notch. On all the cards the back pressure was down to
about 7 or 8 pounds psi.
Notice that the throttle was wide open. The best engineer on the
road was at the throttle. The late A. D. Baker and several of the
railroad company officials were on the train. The engine was a
4-6-2, Pacific type. The size was not known, but it appeared to be
about 100 tons. A couple of the handiest mechanics that
Baker-Pilliod had were riding on a little platform about the
cylinder operating the indicator.
At that time the locomotive began growing. Monster articulated
compounds with boilers nine feet in diameter that left no room on
the sides for the air pumps so they had to be moved to the front
end. There was no room for the injector branch pipes, so the water
was fed to the boiler by pumps and preheated by coils in the smoke
box. The little engine on which the Baker-Pilliod was tested turned
up 1300 horsepower. The giant compounds could develop 6000. The
diesel changed all this and the big locomotives fell under the
junker’s torch. Now we are wondering where the diesel fuel is
to come from. What next?
