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