Author Topic: Back to Steam  (Read 12963 times)

Online crueby

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Re: Back to Steam
« Reply #345 on: November 13, 2017, 09:53:40 PM »
The only critical part is that the valve opens the passage to steam after TDC, and closes it before BDC, how you get there doesn't matter.
And the other fellow is right, the throw on the valve is determined by the spacing of the ports, not the length of the crank. I have a beam engine with very long cylinder, but ports and steam chest are sized like a shorter cylinder.

Offline Brian Rupnow

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Re: Back to Steam
« Reply #346 on: November 13, 2017, 09:59:13 PM »
A short video of the complete Stephensons reversing linkage on my engine.

Offline Brian Rupnow

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Re: Back to Steam
« Reply #347 on: November 15, 2017, 04:35:52 PM »
This thing is kicking my butt!! After adding all the little bits and pieces, now I can't get it to run at all. :cussing: :cussing: I've decided to go back to basics and completely isolate one cylinder and to get it running on one cylinder first, then isolate the running cylinder and set up the other one. This works great if I can get it running on one cylinder, which so far is eluding me. I must be getting close, because in one position that the valve was set, it oscillated. Flywheel didn't go all the way around---It sat there and went back and forth. That's something I haven't seen before. It seems that the secret is getting the steam valve into the right position, which for me has always been at the center of it's travel when the piston is at bottom dead center. Of course the problem is that with the steamchest cover plate in place, you can't see where the valve is, so you have to resort to measuring the amount of steam valve rod extending beyond the gland nut, in it's maximum and minimum positions, then decide on the "happy medium" and set the engine up to run that way.---And of course this may not be accurate either, because without being able to actually see the steam valve, I don't really know if it's centered or offset to one end or the other of where it should be in the steamchest.

Offline Jasonb

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Re: Back to Steam
« Reply #348 on: November 15, 2017, 04:48:23 PM »
Stuarts pdf on how to set up an engine with reversing gear may help

https://web.archive.org/web/20060713173202/http://www.stuartmodels.com/pdfs/SM-Timing.pdf

Also remember that when you turn the engine end for end to set up the second cylinder the crank will be rotating the opposite way as you look at that end

Online crueby

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Re: Back to Steam
« Reply #349 on: November 15, 2017, 04:49:04 PM »
Isolating the cylinders, just feeding air to one at a time, is a great way to go. I like to put in low pressure air, enough to feel the push, and hand turn the flywheel while feeling when the valves open and close. That way I can fine tune the center spot as well as the eccentric angle to the crank. Tiny angle change can make all the difference. A felt tip line on the eccentric and shaft make it easier to tell how much you are moving it.
You valve slider dimensions must be okay since it did run once. Methodical changes one at a time will get you there.

Offline Stuart

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Re: Back to Steam
« Reply #350 on: November 15, 2017, 04:52:52 PM »
Brian

Itís very easy to do
Put it in full gear one way look in valve chest rotate the engine the valve should uncover the port the same at both ends do not worry about the position of the piston at this stage , now put the gear in the other end and repeat if itís not still uncovering the port evenly at both ends then the valve gear is not correct in the dims. To adjust move the valve on the valve rod

If the above is ok then time the valve put the piston at TDC and rotate the working eccentric in the direction you want until the respective port is just uncovered , repeat for with the gear in the direction and repeat with the working eccentric ,remember it now going the other way

Repeat for the other end or test that one , but when you do the other end think about the rotation make sure it matches


I have built a good few locoís with Stevensonís loco link and many more with walschaerts gear

All you need is equal valve movement and the eccentric set so that is just opens the port at TDC

My aim is for a accurate part with a good finish

Offline Brian Rupnow

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Re: Back to Steam
« Reply #351 on: November 15, 2017, 05:56:19 PM »
Thanks guys--I'm trying.---Brian

Offline Zephyrin

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Re: Back to Steam
« Reply #352 on: November 15, 2017, 06:02:06 PM »
No need to see the valve for setting the eccentrics, Brian!

turn the engine crankshaft by hand in the forward direction, when the piston crosses TDC, look at the valves, the forward valve starts to open the upper steam port, and moves in the same direction as the piston (for this short part of the cycle only), even if you don't see the valve, you can see its direction of rotation : downwards, the valve being in advance on the piston.
When the piston passes midstroke, this valve moves now upwards, in the opposite of the piston; this is the valve which corresponds to this rotation.
The same holds true for the second cylinder, for the same direction of rotation of the crankshaft, but looking at the engine from the other side can be confusing as Jason said.
once the eccentrics are roughly set, the engine runs, and the setting are adjusted up to the best...
Zephyrin
my model engineering albums :
https://plus.google.com/u/0/113249908069844921550

Offline Brian Rupnow

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Re: Back to Steam
« Reply #353 on: November 15, 2017, 07:40:14 PM »
AWRIGHT!!! We've-got foreword and reverse on one cylinder. Hooray Hooray---Happy Dance. :pinkelephant: :pinkelephant: :pinkelephant: Stuart--It was your post that done the trick. Thank you so much.---Brian
« Last Edit: November 16, 2017, 12:20:23 AM by Brian Rupnow »

Online crueby

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Re: Back to Steam
« Reply #354 on: November 15, 2017, 10:33:24 PM »
Whahoo!!!

Offline Art K

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Re: Back to Steam
« Reply #355 on: November 16, 2017, 02:16:46 AM »
Brian,
Great that you got it. :whoohoo:
Art

Offline Stuart

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Re: Back to Steam
« Reply #356 on: November 16, 2017, 07:01:18 AM »
Brian

Itís a pleasure thatís what forums are for to help others and to spread our knowledge to others

My aim is for a accurate part with a good finish

Offline Brian Rupnow

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Re: Back to Steam
« Reply #357 on: November 16, 2017, 06:19:42 PM »
Progress report. I have everything back together but the cylinder closest to the flywheel is still acting quite wimpy. I need a break from this before I break out in hives!!! I have to go across town now and do some business, and maybe when I get home later I can try a teensy bit of adjusting on the eccentric on that underperforming side. If I'm really, really lucky, that may be all it takes. Hope--hope.

Online crueby

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Re: Back to Steam
« Reply #358 on: November 16, 2017, 06:42:08 PM »
Progress report. I have everything back together but the cylinder closest to the flywheel is still acting quite wimpy. I need a break from this before I break out in hives!!! I have to go across town now and do some business, and maybe when I get home later I can try a teensy bit of adjusting on the eccentric on that underperforming side. If I'm really, really lucky, that may be all it takes. Hope--hope.

If it is not pushing hard in the up OR down stroke, then it may be that the valve slider is a tad too long, and not opening the port all the way. Or there is a bit of cylinder gasket sticking out too far and blocking the port into the cylinder (done that one a few times!)

Offline Brian Rupnow

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Re: Back to Steam
« Reply #359 on: November 16, 2017, 11:38:49 PM »
Today we had success. The engine ran on both cylinders, forward and then reverse. It's not video worthy yet, but it certainly made my old heart go pitter patter. I had a tough time getting the eccentrics set in the correct position on the second cylinder. I could get it to run, but only clockwise. then I would adjust it a little bit and it would only run counterclockwise. Finally, I played "Around the clock" and moved it in 20 degree increments until I found the sweet spot, where it would run in either direction as dictated by the reversing levers position and in concert with the first cylinder. At the end of the day I scrounged around in my shop until I found a piece of steel to make a second flywheel. I'm not sure if I actually need it or not, but even if I only use it during "set-up" procedures you can never have too many extra flywheels around.