Arnold Throp Corliss Valve setting

[Les#053]

I managed to get this running, eventually, but it had no power which is why the governor belt has been removed in the video.

The engine turns over very easily, in fact only using one finger.

This may seem a silly question but what is the correct direction of rotation for the flywheel, or should it run in both directions?

I made some changes to try and improve things but now can't get it to run at all!

Any help would be much appreciated.


Les


<a href="https://www.youtube.com/watch?v=q8z07UK8PJc" target="_blank">http://www.youtube.com/watch?v=q8z07UK8PJc</a>

[Alan Haisley]

I think you have it running backwards, Les. As it is, it pulls up on the crosshead. If you run it the other way it will push down, which looks like it will be better for that design.

Alan

[kvom]

That's my thought as well.  Such engines are not reversible, but the direction is can be changed by interchanging the front and rear valve settings.

[vcutajar]

You said you did some things to improve it.  Do you remember what you did and backtrack?  I am not an expert but I think the position of the eccentrics and the valves is critical.

Vince

[Les#053]

Hi Alan, Kvom, it doesn't show any inclination to run the other way whereas at least it almost does this way.

Hi Vince, I can't change anything on the eccentrics as they are keyed to the shaft, the inlet valves seem to be operating as they should
so I think the problem is with the exhaust valves.

PS Vince congratulations on your MEM Corliss, a beautiful model, I've read every page of your build and learned a lot.

Les

[crueby]

That's my thought as well.  Such engines are not reversible, but the direction is can be changed by interchanging the front and rear valve settings.

Kvom - Is there something about the corliss valve design that made them not reversible, or just that for a mill engine they did not need to reverse them so they did not bother to install a reversing gear? I'm just learning about corliss valves, gotta build one one of these days!

[kvom]

The valve motion is controlled by the 4 linkages and the single eccentric.  Reversing requires that the phase of valves vs. the piston change 180 degrees, and there is no provision for that on these engines.

Mill engines powering a line shaft, generator,or pump and had no need to reverse.

Since these are rotary valves, and I assume that your model doesn't have trip valves, then each of 4 rotary valves needs to be positioned properly for the desired direction and its motion arm tightened on the shaft. 

[Captain Jerry]

The valve motion is controlled by the 4 linkages and the single eccentric.  Reversing requires that the phase of valves vs. the piston change 180 degrees, and there is no provision for that on these engines.

Mill engines powering a line shaft, generator,or pump and had no need to reverse.

Since these are rotary valves, and I assume that your model doesn't have trip valves, then each of 4 rotary valves needs to be positioned properly for the desired direction and its motion arm tightened on the shaft.

Hi Kvom

I agree with almost everything that you say with one amendment.   As you say, most mill engines have no reason to reverse and therefore most mill engines were designed and built without reversing gear, but that does not mean that it could not be done with Corliss valve engines.  There were many reversing Corliss engines  built, notably in steel rolling mills, where the mill was cycled in both directions as the hot steel slab was rolled.  Any engine where the valve timing is controlled by an eccentric is reversible using one of the many patented gears such as the Stevenson linkage.  But such gear is an unnecessary expense and complication in many applications.

This engine is a bit different in that it has two eccentrics, one for the steam valves and one for the exhaust valves.  This was one more engineering effort in the search for greater economy, but even those engines so equipped could be made reversible with additional valve linkage.

On this model, since there is no way to change the angle of the eccentric, any tuning adjustment has to be made in the links between the wrist plate and the valve control arms or possible in the relationship of the valve edge to the valve control arm.  I agree that it seems to be running in wrong direction which makes me think that second of these two.

There is a lot going on with all that motion and the separate eccentric for the exhaust  adds to the confusion.

Jerry

[Les#053]

I think I mentioned in an earlier thread that this came to me like one of Jo's orphans and was 30-40% completed.

The crankshaft was already completed and I'm beginning to wonder if the eccentrics have been positioned incorrectly as it seems
impossible to reverse the direction as Alan has suggested.

Should the exhaust eccentric lead the inlet, at the moment with the flywheel going clockwise (the only way it will run) it is leading.

Les

[kvom]

Is there some reason you can't move the eccentric setting?  In theory if the engine runs successfully in one direction, turning the eccentric 180 degrees would be a good start to getting it to run the opposite direction.

[vcutajar]

I know that Arnold's MEM Corliss and mine turn in opposite directions.  I have been studying Arnold's photos and comparing them to mine and it seems that our eccentrics are set 180 degrees apart.  So I guess the position of the eccentric dictates in which direction the flywheel turns.

I think Les has said that his eccentrics are keyed to the crankshaft so he cannot reposition them.  Is there a possibility of switching the eccentrics?  What I mean is that can the eccentric that controls the exhaust valves be made to control the inlet valves and the eccentric that is controlling the inlet valve be made to control the exhaust valves.

Just an idea.

Vince

[Les#053]

Sadly it's not possible to swap them over Vince, nothing would line up at the cylinder end.

I think I have to bite the bullet and accept it as it is, or re-machine the key-ways, if I leave it as it is what Alan says is correct, the crosshead will be trying
to lift rather than push down on the slide bed.

What concerns me more at the moment is that, yes it will run but, it has no power and I wonder if that is down to the exhaust valves not operating correctly.

The exhaust valve seem to be almost impossible to set where I would expect them to be so I'm beginning to wonder if the existing key positions are completely wrong.

Les

[kvom]

Are the valve stems keyed as well?  It's hard to see much from the video.

[Captain Jerry]

Les

I would really like to help you work this out but the video is not clear enough for me to do this.  I have watched it and played with it on the original youtube site where it can be played at 1/4 speed and at full screen but it is still to fast.  It would be very helpfull if you could post four still pictures  starting with the crank TDC on the head end and advancing 90 degrees in each of the three following shots.  It is not necessary to show the crank or the flywheel. just from the crosshead and the valve gear on the cylinder. 

Another posssibility would be a video with the engine turning over very slowly under finger power.  Again just the crosshead and cylinder linkage.

I believe that the exhaust valve should lead the inlet but on the video, the lead appears excessive.  Exhaust valve timing is important of course and that is why this design has a separate eccentric for the exhaust.  When I was testing and tuning the valves on my corliss design,  I found out that it is possible to run it without moving the inlet valve.  I had the inlet valve linkage completely disconnected and both valves locked wide open.  Just letting the linkage control the exhaust valve gave a pretty good running engine but of course it was a terrible air hog.

Since this is a salvage job, I am wondering if you have the original plans that show the position of the eccentrics relative to the crank.   It seems to me that the only direction that this crank will run is in the direction that you now have it running but it should be possible to make it run better.

Jerry

[Jo]

These are the timing diagram from the drawings.

Without close up photos of the set up it is difficult to make any suggestions.

Jo

[Les#053]

Hi everyone, thanks for the offer of help, it is really appreciated.

Jerry, I will try to get the photos and video done later today.

Les

[Les#053]

Hi Jerry

Attached is the link to the video, and some not very good photos.

Hopefully you might be able to see what I'm doing wrong!


Les


<a href="https://www.youtube.com/watch?v=Hgggtp7mlhQ" target="_blank">http://www.youtube.com/watch?v=Hgggtp7mlhQ</a>

[vcutajar]

Les

I have been looking at you latest video in slow motion.  I do not know if it matters or maybe it's an optical illusion.  I noticed that the left hand inlet valve moves more than the right one.  In fact it seems that at some point it disconnects from that central pivot arm.

Vince

[Les#053]

Hi Vince

Yes you are right, that is the last video I have of it running and I think that was one of the things I thought I was correcting
and I haven't had it running since.

Serves me right for making multiple changes without testing between them!

Just found the answer to one of my questions, there is a note on the drawing to say that the steam eccentric leads the crank by 42 degrees and the
exhaust follows by 45 degrees.

I decided to try and check this, the only way I could think of without dismantling the crankshaft was to count the barring teeth on the flywheel as they looked fairly even.
I set the steam eccentric to its high point using a DTI and marked a tooth, I then moved the crank to the vertical position and counted the teeth.

96 barring teeth = 3.75 deg/tooth X 14 teeth = 52.5 deg for Steam and 11 teeth = 41.25 for Exhaust

Can anyone see any glaring errors in this fairly crude method?


Les

[Captain Jerry]

Les

Thanks for the new pictures.  Very easy to see and analyze.  There is one more piece of information that is needed.   That is where does the valve actually open?  It appears from the pics that the valves use inside admission but it is impossible to actually see the valve in relation to the control arms which are very visible.  Full size corliss engines have a witness mark on the opposite end of the valve stem that shows this.  The bonnet on the other side of the cylinder must be removed  to see it. Here is aa link to an article that gives a lot of detail on vaalve adjustment.  You will have to go down to figure 877 and 878 to see this.  There is a lot of additional information that pertains to valve gear that is quite different from yours.  Don't let it confuse you.  If your model does not have these marks you may want to look into it.  It is a critical piece of the adjustment.  It is usually adjusted  by loosening the steam arm on the front of the cylinder and rotating it in relation to the valve.

My guess at this point is that is where the problem lies and when that is set properly, the engine will run in the right direction.

I do not claim to be an expert on this subject but I have invested a lot of time reading as much of the old literature as I can find in order to get a couple of Corliss engine to run.  A lot of the older articles a difficult to understand and may need ro be re-read a time or two or more.  Thanks to the internet all of that expertise is available.  Keep us posted on your results.  I am truly interested.

By the way, that is a very nice model with a lot of interesting mechaanical detail that I have not seen.  One of the reasons that I like Corliss engines is the great number of ways that were devised to do the same thing.

Jerry

[Les#053]

Hi Jerry

Picture one shows the left hand exhaust just beginning to open and the right hand one fully closed, picture two shows the right hand side.

It seems to be impossible to stage the inlets for a picture as they are held apart by a spring between them and I ran out of hands.

I've included a PDF of the theory if everything had been made to dimension.

You mentioned about a link to an article but I can't seem to see it.


Les

[Captain Jerry]

Les

My apologies for not including the link to the referenced article.  Here it is:

http://www.wkinsler.com/technology/corliss/figures/index.html

I hope it makes sense.  The witness marks on the opposite end of the valve shaft makes it possible to see exactly when the valve opens or closes.   Just to re state the situation, with the bonnet on the backside of the cylinder there should be a witness mark on the frame that corresponds to the opening edge of the valve face.  On the end of the valve shaft, there should be a witness mark that corresponds with the leading edge of the valve.  If there are no such marks, it would be very worthwhile to create them, even if it means taking the valve apart.

From looking at the second video and the first set of photos, my best guess is the position of the arm on the front end of the valve shaft is not correctly set,  This is probably true on all four valves.

Jerry

[Captain Jerry]

The reference marks are also shown in figure 960.

[Les#053]

Jerry

Thanks for the link, really interesting article, if what you need to know about Corliss valves isn't there it isn't anywhere.

I've been doing a lot of thinking and decided that if those eccentric keys are really as far out as I believe they are I'm never going to get this running right.
It would also explain why I can't seem to get the exhaust valves synchronised with the steam valves.

So, reluctantly, I'm going to do a complete strip down, check those key-way positions accurately and do a few other things such as put those valve position markings in, make
a few new gaskets etc.

It maybe a little while before I have any progress to report as I'm quite slow and don't get as much shop time as I would like.

Will keep you posted on the outcome Jerry.


Les

[Captain Jerry]

Les

Congratulations on your decision to work it out.  If things don't seem to be working like they should, you need to get to the bottom of it.  The eccentrics may be a part of it but your measurement of the angles show that they are set pretty close to the design and I think your method was valid.  It seems odd that they are keyed in, particularly as the reference source shows a setup called "squaring the valves" that involves adjusting the eccentrics.

Good luck with your investigation.  I know that the referenced source will be a great  help as it has been for me.

Jerry

[Les#053]

Still can't get this engine to run in the correct direction, and as Alan commented this means that the crosshead is pulling up into the keep plates rather than down into the bed.

Either I have interpreted the drawings incorrectly (a distinct possibility) or the drawings are at best misleading.

Picture N01 shows the information given on the plans, I've assumed from this that the crank is at TDC as shown in picture N02 Fig A.

Earlier in this post Jerry suggested that he believes the exhaust should lead the inlet and as he is clearly very knowledgeable on Corliss valve gear I intend to take his advice and modify
the keyways accordingly.

What I can't decide is whether to follow Fig B and leave the leading and trailing angles the same, or follow Fig C and swap the angles as well.

I have been in touch with Bob Potter from Southworth Engines who has been very helpful and sent me loads of pictures, but he hasn't got this far on his engine yet
and as he says people don't always notify him of any errors found. He is very kindly trying to contact people he knows who have completed the engine but has not got back to me yet.

Any ideas would be much appreciated


Les

[Les#053]

Well I did wonder at times whether I would ever get there, it still needs some fine tuning as it doesn't run that smoothly,
hopefully it just wants running in. It seems to need a lot of air, 25 PSI and will not tick over very slowly.

My thanks to Colin Palmer for the pictures he sent me, they really helped, and to Terry Fleet for the chat we had on the phone,
it was his suggestion that I might have the valves 180 degrees out that was the turning point, I had indeed got the inlet valves wrong.


<a href="https://www.youtube.com/watch?v=le5HtngczSk" target="_blank">http://www.youtube.com/watch?v=le5HtngczSk</a>

[vcutajar]

Glad you managed get it running.

Vince

[Alan Haisley]

An engine that pretty SHOULD run!

[crueby]

That is VERY nice! Wonderful sound to it.

[Les#053]

Thanks guys, I just wish I could get it to run as smooth as your Corliss Vince!

Les

[crueby]

The corliss valves are very sensitive to throw distance and timing, spent a lot of time on mine as well tweaking all the settings.