Steam & Excursion > 3 Cyl. steam loco ?????

On regular 2 cyl. steam loco the drivers are "quartered" I understand the reason for this. What about 3 cyl. locomotives with the 3rd cyl in between the frame members and driving a "crank" on the axel. Are the outside journals still "quartered" or is the angular displacement of the 3 journals set at 120° from each other?

Old Bob out in Lost wages

Theoretically 120 degrees but you'd have to compensate for the angle of the middle cylinder,
drag out both the trig and geometry books because the means of compensation would then
be the stroke of the middle cylinder and/or the crank angle.

Out

Thank you Sir!!

You might want to refer back to this discussion from a few months ago
 
http://www.trainorders.com/discussion/read.php?10,3962660,3964050#msg-3964050

-John

The center cylinder on SP 4-10-2s and UP 4-12-2s
was inclined 9.5 deg, so the cranks on the second
driver axle were presumably at 120-129.5-110.5 deg.

But did that or didn't that result in equally spaced strokes?  I mean, if the 3rd cylinder lay in the same plane you'd do 120° spacing, no?  So just adjusting for the different angle should result in the same thing effectively, no?

filmteknik Wrote:
-------------------------------------------------------
> But did that or didn't that result in equally
> spaced strokes?  I mean, if the 3rd cylinder lay
> in the same plane you'd do 120° spacing, no?  So
> just adjusting for the different angle should
> result in the same thing effectively, no?

Yes. The thing that "fools" listeners concerning 3-cylinder steam locomotives is the uneven exhaust sound, i.e. that "3-cylinder gait". The uneven exhaust is caused by the much shorter distance that the steam exhausting from the center cylinder takes to the exhaust nozzle, when compared to the greater distance of the exhaust steam from the two out-side cylinders. Having ridden behind a 3-cylinder steam locomotive in Germany, there is no "uneven" power stroke sensation, as compared to the characteristic uneven exhaust SOUNDS.

That's the reason for all the gymnastics on the cylinder angle and crank angles, to try and balance
out the force vector from the middle cylinder against the other two to reduce that surge or vibration
from the middle cylinder.

Out

How about 4-cylinder balanced compounds with two inboard high pressure and two outboard low pressure cylinders?  How were the cranks arranged to balance the forces there?

And didn't some 4-cyl compounds have piston valves
for the two right-side cylinders on one valve shaft? If
we were smart enough maybe we could figure out
how the pistons had to be phased. Dunno if 4-cyl
compounds always had the two right-side cyl
180 degrees apart, but one English class of 4-cyl
simples had some sort of 45-deg/135-deg layout.
Was it the SR Lord Nelsons?

You'd almost think you could 90 degree that four cylinder compound because the losses
could be figured so that the HP exhaust into the LP cylinder would give the same applied
force (diameter puzzle) and you wouldn't even have to valve the LP cylinders as the 90
degree timing would give equal thrust to all four cylinders ie LP works at 50% of HP so
that back pressure would dampen the pulsations, your results may vary, write if it works.

Out

> But did that or didn't that result in equally
> spaced strokes?  I mean, if the 3rd cylinder lay
> in the same plane you'd do 120° spacing, no?  So
> just adjusting for the different angle should
> result in the same thing effectively, no?

Same as what?

We'd like to have one cylinder at front
dead center at 120-deg intervals of driver
rotation. Only way to do that if the center
cylinder is inclined is to shift the crank
angles correspondingly.

Evan_Werkema Wrote:
-------------------------------------------------------
> How about 4-cylinder balanced compounds with two
> inboard high pressure and two outboard low
> pressure cylinders?  How were the cranks arranged
> to balance the forces there?

Is this what you're looking for?

-John

---

LarryDoyle Wrote:

> Is this what you're looking for?

Thanks!  So inboard and outboard were 180 apart - would the two sides have been set 90 degrees apart?

Evan_Werkema Wrote:
-------------------------------------------------------
> LarryDoyle Wrote:
>
> > Is this what you're looking for?
>
> Thanks!  So inboard and outboard were 180 apart -
> would the two sides have been set 90 degrees
> apart?

Shooting from the hip, my immediate answer would be "Yes, inboard and outboard on each side would be 180 degrees apart."

BUT...  Studying the diagram, it appears the draughtsman has shown the inboard HP piston (12) and outboard LP piston (14) to both be at midstroke, the angularity of the rods thus causing both the exterior main pin AND the inside main pin to each be  apx. 1 degree forward of their vertical positions.

My dilemma is, what happens 180 degrees later?  I would seem to me that both main pins would then be apx. 1 degree backward of their vertical positions, and thus the pistons would be somewhat separated from their centered positions.  This seems highly irregular!

Did the draughtsman  get it wrong?  Or, is there something about the timing on these engines I'm not seeing????

-John

The cylinder stroke vs angular displacement doesn't even look close, that and I'm getting crosseyed
looking at that diagram. Why would you 4 cylinder compound when you could just increase the normal
cylinder diameter simple and dismiss that pile of valve gear?

Out

callum_out Wrote:
-------------------------------------------------------
> The cylinder stroke vs angular displacement
> doesn't even look close, that and I'm getting
> crosseyed
> looking at that diagram. Why would you 4 cylinder
> compound when you could just increase the normal
> cylinder diameter simple and dismiss that pile of
> valve gear?
>
> Out

The objective of any compound is to improve efficiency.

You bet, that's why you see so many in the modern era of steam!

Out

I think compounding arose just before general acceptance of superheating.  One has nothing to do with the other; you can certainly user superheaters with compounding as all the later Mallets did and increase efficiency with both techniques but they probably were happy with the efficiency they got with superheating alone and, for the most part, cast aside compounding and its mechanical complexities.

To John's point and mine on the 4 cylinder arrangment, because of the exhaust and the lack of ability
to put the larger low pressure cylinders inboard you end up with the high pressure valving inside. Just
makes maintenance a total headache also somewhat limits the size of the high pressure cylinders, just
doesn't seem like an overall good idea.

Out