Author Topic: Working Corliss Valve Release  (Read 8621 times)

Offline Captain Jerry

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Working Corliss Valve Release
« on: January 29, 2013, 07:23:12 PM »
With so many Corliss engines under way or planned,  I thought that it might be a good idea to open a thread devoted to just the valve gear.  There are many different types and all very interesting.  I have been working on a Corliss engine for about 6 months that I hesitated to call a Corliss because I doubted that I could build a working valve release at that scale.  As it turns out, I was right.  I should have gone for a slightly larger cylinder so that I could make something that would work and still fit in scale.

The MEM-Corliss as designed by Mods seems about right.  It uses the same 1/4" valve bore that I used on my small design but the cylinder block is about 75% bigger and that leaves a lot more space between the valve centers and the wrist plate center for the release linkage.  I think something smaller than the MEM design and a little larger than mine could work also.

Here is model that incorporates features from a number of full scale engines, many of which are very similar.  In the video, the control rod on the left should be attached to a governor but is at the moment attached to my left hand.  I controls the cam angle and the point of release.  The rod on the right should be attached to the wrist plate to provide the rocking motion that rotates the valve but in this case is attached to my right hand.

Be sure that your sound is on!



The above is a Photobook link.  If you prefer YouTube, try this link

 http://youtu.be/8dr1CLpzmiU     
 
I hope you can put up with the crude finish and photography but this is just a proof of design, not a finished model.

The release is an important part of the action but without the re-latch on the return would be useless.  The re-latch was as much of a problem to get to function reliably but right now I am satisfied with the overall design.  I do need to make a few changes.  The governor control arm should be slightly longer so that it does not interfere with the hook spring, and the lower arm of the double arm could be slightly shorter for scale considerations.

Jerry

I hope that as other people get to this stage of the build that they might add to this thread as well.   Crab Claw, Oval Arm, Half Moon, Musgrave, Bates and other styles are worth seeing and analyzing.
« Last Edit: January 29, 2013, 07:35:49 PM by Captain Jerry »
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Offline ScroungerLee

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Re: Working Corliss Valve Release
« Reply #1 on: January 29, 2013, 07:34:12 PM »
Thank you Jerry, that was very helpful.

Lee
Mmmmm.... Shiny!

Online pgp001

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Re: Working Corliss Valve Release
« Reply #2 on: January 29, 2013, 08:47:55 PM »
By Jove I think he's got it.  :ThumbsUp:

Phil

Offline mklotz

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Re: Working Corliss Valve Release
« Reply #3 on: January 29, 2013, 09:45:48 PM »
Bookmarked.  Kudos to you.  This was very much needed and is very appreciated.

Let me encourage you to continue with further explanation.
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Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #4 on: January 30, 2013, 01:23:38 AM »
Thanks, Marv.  It doesn't take much encouragement to get more from me. I had hoped that this would encourage participation from some other builders.  I have been working on this part of the design problem for several months and except for some very useful information from Bob (Maryak) the only sources of detailed information has come from very old text with poor clarity and limited views or from video of museum pieces.

Surely, with all of the obvious interest in this type of engine, some other members have given the fiddly parts more than just a passing thought.  This design, although it seems to work,  needs some refinement and I will probably build several iterations before deciding to start work on another engine.

I will post more as it develops.  The semi success of this model has been made possible by developing some fabricating techniques to hold and shape these small parts, mostly hand work, and modifications to the plan to reflect what was possible for me.  My methods may be a little crude so any comments that  might make it easier, better or more accurate should be posted.  Not just to help me but to help everyone.

Jerry
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Offline steamer

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Re: Working Corliss Valve Release
« Reply #5 on: January 30, 2013, 02:34:14 AM »
Well done Jerry!

 :praise2:

Dave
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Online Jo

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Re: Working Corliss Valve Release
« Reply #6 on: January 30, 2013, 07:22:17 AM »
Nice Jerry :ThumbsUp:,

Looks like I might need to get my skates on and put together sufficient of the engine show the trip C3.

Jo
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Offline black85vette

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Re: Working Corliss Valve Release
« Reply #7 on: January 30, 2013, 01:27:51 PM »
Thanks.   I had no concept of what this looked like or how it worked.

Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #8 on: January 30, 2013, 04:22:42 PM »
Nice Jerry :ThumbsUp: ,

Looks like I might need to get my skates on and put together sufficient of the engine show the trip C3.

Jo

Don't let me rush you.   I really want to see it done because you have a knack for dealing with the small bits, and also because the Musgrave gear is a much different way to achieve the same result.

Jerry

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Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #9 on: January 30, 2013, 04:59:00 PM »
I really should have posted a better explanation of the demonstration, but it had gotten very late and my concentration was fading. 

In the first part of the video, the governor arm was held relatively steady and the cutoff was occurring just short of mid stroke.  The release occurs when the cam has pushed the hook off of the latch stud.  You can hear the metal clank when the dashpot rod (the vertical rod) hits bottom because there is no dashpot fitted.  One of the purposes of the dashpot is to cushion the rod as it hitts bottom.  As the hook reverses its rotation and lowers over the latch stud, you can hear the click as the hook reengages.   That is where the characteristic Corliss sound comes from.

Towards the end of the video, you can see that I have move the governor control arm to the left.  That changes the point at which the release occurs giving a longer opening and more power.  You can also see that if it is moved too far, the release does not occur at all and the valve closes slowly.  This maximum cutoff point is at about 50% of the piston stroke.  If the cam follower has not hit the governor cam and kicked the hook off of the stud before the valve gear reverses it rotation and starts the closing, it never will.  Except for engines equipped with specialized high speed gear.  If this is occuring, the engine is way undersize for the load, and the efficiency of the Corliss gear is completely lost.

Ideally, the release and cutoff should happen at 20%-25% of the piston stroke.  In the final part of the video, I have moved the governor control to the right which causes the cam to make contact earlier.  You can see that the valve rod barely starts to open when the release occurs.  This represents a light load condition, when less power and less steam is required.

When I titled this a "Working Corliss Valve Release",  That may have been wishfull thinking.  Yes, the hook will drop the valve but whether I can actually get the governor to provide the fine control necessary remains to be seen.  Veeerrry doubtful.

Later tonight, I will try to post some pictures of the individual parts and their relationship.

Jerry
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Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #10 on: February 07, 2013, 01:55:45 AM »
Here is one more possible Corliss valve release mechanism.  It is my interpretation of what I believe is the Bates Toggle Release.  I have read several verbal descriptions and have seen only one drawing of the design.  There is one YouTube video of a Bates Corliss engine but that engine does not appear to use this type of release.



I have not built this design yet but it seems like it would be much easier to fabricate than most that I have seen.  There are no sliding catches or release/latch mechanism and no springs.  It relies on a toggle in the valve rod which is locked over center to open the valve and which is de-toggled at the point of cutoff, allowing the dashpot to drop and close the valve.  In the above CAD model, the wrist plate is rotating clockwise and the steam valve is opening.  It has not yet reached the cutoff point, but when the tail lever of the gold colored link hits the red limit stop, the link will de-toggle and the valve will drop closed.  The valve on the right was de-toggled on the previous counter-clockwise phase and is closed. As the wrist plate continues its clockwise rotation the link will go over center and lock in for the next cycle.  The position of the Red limit stops is fixed in this drawing but are movable under governor control for variable cutoff.

For size comparissons, the cylinder block is roughly the same as the MEM-Corliss (2.5" long) but is of slightly different design.  The diameter of the valve bonnets is .5" (12mm) and the diameter of all rods is 5/64"

If anyone has any more information or a clear drawing or photograph of the Bates release, it would be nice to see.  I am still researching various designs.

Jerry
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Offline tvoght

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Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #12 on: February 07, 2013, 03:52:15 AM »
Tim

Thanks for the effort to uncover that.  It appears to be a patent awarded to Thomas Wright which was assigned to the Bates Machine Company but that one has much more in common with other release mechanisms in that it relies on contact between hardened blocks on opposed parts that engage like a ratchet and pawl or a trigger sear mechanism.  That seems to be almost a universal feature of the various designs that I have researched but even in full size machines, the relative movement to disengage the latch is in the small fractions of an inch which means that the tolerances are very tight.  When reduced to 1:24 scale, the relative movement is invisibly small and the tolerance is impossible.  Which means that building at small scale requires the mechanism to be built way over scale. 

I think that I have seen that mechanism referred to as the Bates "Inertial" Gear because it relies on the inertial of the parts to close the latch instead of a spring and that is said to increase the reliability and the speed of the re-latch.  The speed limitation of Corliss machines seems to have been a result of the gear failing to re-engage at high speeds causing the valve to fail to open and this one is touted as a "High Speed" gear.  The Bates Machine Company seems to have built Corliss engines and other types under several different patents

The one that I have modeled (drawn) and am researching is a toggle mechanism that folds instead of disengaging.  It is like when you stand with your knees locked.  If some one hits you in the back of your locked knees, your legs fold and you fall down.  Your legs are not disconnected and you can stand up and lock them again.  It looks like it could be built the way that I have drawn it but there may be something I don't see. 

Thanks for the help.

Jerry

« Last Edit: February 07, 2013, 03:56:41 AM by Captain Jerry »
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Offline Captain Jerry

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Re: Working Corliss Valve Release
« Reply #13 on: February 07, 2013, 04:16:05 AM »
Here is a link to a description of the "folding toggle" linkage

http://www16.us.archive.org/stream/handbookofcorlis00shilrich#page/192/mode/2up

Jerry
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Offline tvoght

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Re: Working Corliss Valve Release
« Reply #14 on: February 07, 2013, 05:01:31 AM »
While I'll admit to only a marginal understanding of Corliss valve gear, I think the following patents (to Albert J. Bates) come closer. In particular, the drawings in the second (US505153) bear a strong resemblance to the figures in the book your referenced.

US436768:

http://www.google.com/patents/US436768?printsec=drawing&dq=436768&ei=hi8TUZ2YLoe9yQGXqYCwDw#v=onepage&q=436768&f=false

US505153:

http://www.google.com/patents/US505153?printsec=drawing&dq=505153#v=onepage&q=505153&f=false


Hope it's useful,
--Tim