Bilgram's valve diagram a graphical method to design a steam valve

[Dan Rowe]

I struck up an offline conversation with Chris about the valve gear for the Sabino because he made a comment that he wanted to make this engine with a lot of detail. The only valve gear I have really studied is Stephenson link motion. This is mainly because of my interest in Shay locomotives which are essentially a marine engine on a locomotive. The very first Shay built by Ephraim Shay was a marine engine on a flatcar. A Shay locomotive is really just a marine engine that got lost in the woods.

When I discovered Bilgram's diagram I was thrilled as I thought my struggle to learn valve gears was ended. Bilgram's diagram is a powerful tool to design a steam valve but it does not really help in the design of the rest of Stephenson link motion or any other type of reverse gear.

It was easy for Chris to get accurate measurements of the link motion but when I asked about the angle of advance he gave me an approximate number because it is not really possible to say looking at a built engine where the center of the eccentrics are in relationship to the crank pin for the cylinder. 

If the eccentrics were keyed to the shaft and fixed like a Shay and this was an IMPORTANT detail to the builder then the angle of advance would be a key piece of information. Lucky for me the valve travel and the angle of advance are listed on the drawing card index for every Shay.   

With those two numbers and knowing that Shays used 1/16" of lead, I can calculate the cutoff for that Shay. I do not think it is a coincidence that this is true.

I was not sure what would be a good number for the cutoff for this engine but in the book "Machine Drawing and Design" by William Ripper, there is a design for a two cylinder launch with all the parts and a Zeuner diagram. I thought I could simply look at the Zeuner diagram and state the angle of advance but it is really not quite that easy even if you have drawn that diagram as a learning example. I took the easy way out and drew a Bilgram diagram using ONLY the valve travel, the outside lap, and the lead. This worked to 74.92 degrees.

I also told Chris that for model engines it is customary to set the lead to zero. This is a match to the advice given by Dave on the Sabino thread.
                                                                                             

The last indicator card for Sabino that I saw was 75% cut off and just a smidge of lead.     I would dispense with the lead on an engine this small.   
Dave

More on how to use a Bilgram diagram to design a steam valve in the next post.
Cheers Dan

[crueby]

This should be an intersting journey, looking forward to the diagrams and methods!
Chris

[Admiral_dk]

A Shay locomotive is really just a marine engine that got lost in the woods.

       Thank you for that laugh Dan 

Per

[crueby]

A Shay locomotive is really just a marine engine that got lost in the woods.

       Thank you for that laugh Dan 

Per

Then a Lombard is just a train on portable tracks!

[Dan Rowe]

Per, I just really wish i was the one who came up with that phrase but It was Dave Latrope circa 2005 where I got it from.

Chris some Lombards like the Phoenix have vertical cylinders so a Shay on endless tracks.

As I mentioned I only used three numbers to calculate the cutoff for the Ripper launch engine.
1) Valve Travel
2) Steam or outside lap
3) Lead or the amount the valve is open at TDC

Most readers will know that TDC stands for top dead center and BDC stands for bottom dead center. This gets rid of the clumsy naming found in a lot of old steam books where the ends of the cylinder are called crank end and head end. A steam engine had a head at both ends. I am mostly interested in vertical engines so I draw valve diagrams with TDC at the top and BDC at the bottom.

Here is the Bilgram I drew to find the angle of advance of the Ripper launch engine.



Cheers Dan

[derekwarner]

Thanks Dan...I understand the geometry OK , but will be interested as to where some of the missing values are resultants of what?   

Derek

[crueby]

Also once you get farther along, can these diagrams predict what effects notching in the Stevenson link does?

[Dan Rowe]

Derek, I am scratching my head as to what you are asking. If you mean missing values for the Ripper launch engine they can all be found in the book. If you are talking about the Sabino the plan is to work the whole valve solution using the Ripper book as an example.

Cheers Dan

[derekwarner]

Thanks Dan....I had not heard of the Publication......this is my only find  Requium for the Little Ripper Launch Engine


https://books.google.com.au/books?id=6xNUEAAAQBAJ&pg=PT31&lpg=PT31&dq=Ripper+launch+engine&source=bl&ots=6Sc7K7QiEo&sig=ACfU3U2ufjRq5wHyU0JVIzFc2F9AXqkPhw&hl=en&sa=X&ved=2ahUKEwjWyduo1433AhWWzjgGHWjUAwoQ6AF6BAg8EAM

Derek

[Dan Rowe]

Derek, wow that is NOT the book I was talking about.
This is the one and the link should open to the Zeuner diagram for the engine.
https://archive.org/details/acourseinstruct00rippgoog/page/n184/mode/2up

Unfortunately, some vandal Ripped off the color plates of the engine which are the real gem of a very fine book on the art of drafting. (and I DO mean art)

Here is a link to ART prints of the work that shows even more views of the Ripper launch engine.
http://gouldstudios.com/me_SteamLaunch.html

Cheers Dan

[Dan Rowe]

Also once you get farther along, can these diagrams predict what effects notching in the Stevenson link does?

Chris, good question. The short answer is no in this thread we are designing the steam valve. It could be used for a single eccentric engine or any type of reversing gear.

To see what happens by notching back it would be best to use a program like Docksteader to see and compare the output curves.

Now when looking at the curves made by Docksteader's program how do you know when you change a variable if the change made the situation better or worse? It took a bit of thinking about that and the best I could come up with was to use the slip eccentric module for the same engine. A slip eccentric simply shifts the eccentric so the engine acts like a single eccentric engine and the curves look like a single eccentric solution. So my theory is if the change makes the reverse gear design look more like the slip eccentric curves then the situation is better and if the curves look less like the slip eccentric curve then you have made things worse.

The motor that drives Docksteader's program only goes in one direction so it is possible to turn a steam engine into a compressor by shifting the eccentrics far enough. I have done this and it is weird. (It is a program that is fun to throw a monkey wrench into)

The other way to see what happens when by notching back is to make a model. It was common to make a partial engine model to do just that in the days of steam. Now with 3D cad it is even easier to make a full model to see what is up with notching back with Stephenson link motion.

Now to get completely long-winded... The most common way to connect the eccentric rods for Stephenson link motion is with open rods. With open rods, the lead increases from full gear to mid gear. With crossed rods the lead decreases from full gear to mid gear. Open rods are the most common way to set up Stephenson gear. It is simple to change to crossed rods by simply shifting both eccentrics by 180 degrees. It would be interesting to check on what happens to the valve positions for both crossed and open rods to see what happens by flipping the eccentrics at several different angles of the crank.

Cheers Dan

[Dan Rowe]

I like to read about the career path of the engineering authors I have on my shelf or at least what it says in the front of the book. William Ripper was a Professor of Mechanical Engineering at the University of Sheffield.  The other book on my shelf by Ripper is "Steam-Engine Theory and Practice"
I have the fourth edition published in 1905. It is a very modern approach to the study of the steam engine that includes thermodynamics. I know that the last word made some readers think "not for me" but it is a good book and one of the best I have read on the subject and it is technical but not as hard to read as some later books on the thermodynamics of heat engines.

Cheers Dan

[crueby]

Also once you get farther along, can these diagrams predict what effects notching in the Stevenson link does?

Chris, good question. The short answer is no in this thread we are designing the steam valve. It could be used for a single eccentric engine or any type of reversing gear.

To see what happens by notching back it would be best to use a program like Docksteader to see and compare the output curves.

Now when looking at the curves made by Docksteader's program how do you know when you change a variable if the change made the situation better or worse? It took a bit of thinking about that and the best I could come up with was to use the slip eccentric module for the same engine. A slip eccentric simply shifts the eccentric so the engine acts like a single eccentric engine and the curves look like a single eccentric solution. So my theory is if the change makes the reverse gear design look more like the slip eccentric curves then the situation is better and if the curves look less like the slip eccentric curve then you have made things worse.

The motor that drives Docksteader's program only goes in one direction so it is possible to turn a steam engine into a compressor by shifting the eccentrics far enough. I have done this and it is weird. (It is a program that is fun to throw a monkey wrench into)

The other way to see what happens when by notching back is to make a model. It was common to make a partial engine model to do just that in the days of steam. Now with 3D cad it is even easier to make a full model to see what is up with notching back with Stephenson link motion.

Now to get completely long-winded... The most common way to connect the eccentric rods for Stephenson link motion is with open rods. With open rods, the lead increases from full gear to mid gear. With crossed rods the lead decreases from full gear to mid gear. Open rods are the most common way to set up Stephenson gear. It is simple to change to crossed rods by simply shifting both eccentrics by 180 degrees. It would be interesting to check on what happens to the valve positions for both crossed and open rods to see what happens by flipping the eccentrics at several different angles of the crank.

Cheers Dan

Do you have a picture or drawing showing the difference between open and closed rods? I've not heard those terms before.   

[Dan Rowe]

Chris, I can sketch one up it will be quicker than scanning Cecil H. Peabody who was the head of the Marine Engineering Department at MIT. If you have the book "Valvegears for Steam Engines" by Peabody turn to Plate XV in the back and read page 41 for the explanation. I can get this for the next post. The Sabino has a piston valve with inside admission and that is a new one for me and as you already know that flips the eccentrics just like switching to crossed rods.

With the suggested 75% cutoff and zero lead here is the preliminary Bilgram for the Sabino.



Notice that the angle of advance is now 30 degrees. This will be the case for any steam valve with 75% cutoff and zero lead.

I have made a physical analog of the Bilgram diagram in my head so I can easily make changes to see what is going to change with the valve.

I think the valve travel line is a pole. The steam lap is a tetherball. The angle of advance is the string supporting the ball. The lead is how much distance the ball is from the pole. With zero lead the ball is touching the pole. The Ripper launch is shown with 1/4" lead so that is the distance the surface of the ball is from the pole. For me, this works well so have a whack at the ball to see what happens.

Cheers Dan

[crueby]

I think I am seeing more of the relationships, check if I am right. Given the valve travel, if a certain cutoff is desired then the Bilgram could be drawn and the required lap and advance angle calculated? From that port size and valve sizes could be designed to match?

[Dan Rowe]

Yes Chris, if you have a desired cutoff number, draw a horizontal line at the desired percent of the stroke. Then draw a line from the center of the pole to the intersection of the horizontal line and the valve circle. The ball ALWAYS has the center point somewhere on the valve circle. So if there is zero lead the ball is tangent to both the pole and the cutoff line just constructed. With lead simply make a second pole the lead distance away from the original pole and the ball is tangent to the cutoff line and the new lead pole.

The main book I use for Bilgram is "Slide Valve Gears" by Frederic A. Hasley
https://www.google.com/books/edition/Slide_Valve_Gears/xtIXAAAAYAAJ?hl=en

Hasley was an engineer for the Rand Drill Company and went on to be the editor of "American Machinist"

See page 38 'Laying Out The Slide Valve' This describes how to use a full Bilgram diagram to layout the slide valve The only thing, not on the Bilgram diagram is the exhaust valve width. (this is a vertical engine the exhaust valve verticle length is the missing dimension)

I have a copy of the book and I will give the page numbers needed to follow the discussion as it progresses.

The next step is to layout the inside lap. Again we will look at the Ripper launch and use a similar proportional inside lap.

Cheers Dan

[Zephyrin]

This diagram is a very simple and clever way to determine angular advance, but it is not an absolutely exact solution, as the rod angularities are not taken into account.
ie : At 90° of the crank, the piston ( or the valve ) is not precisely at its mid stroke, but a little bit late in running forward, or in advance in the opposite direction.
This is discussed p 88 in the book you've mentioned.
This error is negligible for most steam engine with long valve rods, but if the aim is formal accuracy, more than building steam models (that I enjoy), these calculations are required.

[Dan Rowe]

Zephyrin, thanks for stopping by and yes that is all true. Bilgram does not take into account the angularity of the connecting rod or the eccentric rods. This is why Part I of the text starts with a scotch yoke for both the eccentric and connecting rods to simplify the discussion.

Bilgram's diagram will give the same EXACT answer as a Zeuner diagram or a Reuleaux diagram. The main advantage of a Bilgram diagram is simplicity which allows a physical analog to help visualize what will happen when the variables are changed. As can be seen, a Bilgram construction will simply solve the relationship between the angle of advance, the lap and lead, and the cutoff.

A Zeuner diagram is not as easy to construct and it at least for me, is not easy to visualize what will happen with changes. It is handy to compare designs as there are a lot more published Zeuner diagrams than all other types of valve diagrams.

The discussion on this thread is only about Part I of "Slide Valve Gears". The angularity of the rods is discussed starting on page 45. This part might be important to fine tuning a solution but the valve will work satisfactorily without this extra consideration.

The section that Zephyrin mentioned is in Part II of the book. This section is for shifting and swinging eccentrics. In this section, there are several drawings of more complex valves with extra passageways and extra sliding parts of the valve. On page 80 the author says that the only American firms employing a shifting eccentric, are Armington and Sims and Russell (Giddings). So yes in the case of this type of valve gear it might be a good idea to consider the extra work to design the valve.

Cheers Dan

[Zephyrin]

Hi,
I'm totally with you for the graphical diagrams of Zeuner or Reuleaux when compared to the Bilgram one ! the way you present it really clear, thanks to share your efforts...
I did many model steam engines, from published plans or from my own, and it was always a great pleasure to try to improve the steam distribution, with all these constrains...

[Dan Rowe]

Zephyrin many thanks for that fine comment. This is not the first time I have written on this subject but this time I am trying to make this subject as clear as possible. Reader feedback is more than welcome to help keep this clear and simple.

Now to add exhaust lap to set compression and release. I am not sure what would be a good percent stroke for compression and release which is what inside or exhaust lap sets. I checked the Ripper launch and the inside lap ball is 9.5 degrees wide. I rounded that to 10 degrees for no real reason except to have whole numbers for the angles.

Here is the construction with inside lap which is a ball inside the steam lap ball. Just like the steam lap the center of the ball is on the valve circle and the inside lap has the same center point as the original lap ball.



Now I added a half-circle with the center point that is half the valve travel and is tangent to the steam lap ball. This is labeled port opening circle. The radius of the port opening circle is known as the port opening.

Now, this next bit is somewhat tricky as the words I will use seem like they mean the very same thing. The port opening is defined as the distance of the extreme edge of the valve at full travel to the extreme edge of the steam port. The other term is the port width which sounds like the same thing. For the initial layout of the valve, we will assume that port opening is equal to port width so the valve at the end of travel just completely opens the steam port no more no less.

In the next post, we will start laying out the valve with the starting point of full valve travel to reinforce the concept just made.

Cheers Dan

[Dan Rowe]

Now it is time to change books to “Audels Engineers and Mechanics Guide 1” This is where I first learned about the Bilgram diagram and there is a reference to Mr. Halsey’s book on slide valve gears, so I tracked down a copy. I also tracked down a copy of Hugo Bilgram’s book “Slide Valve Gears” 1878. This is the very same Hugo Bilgram that invented a faster way to make bevel gears using a modified shaper to generate the teeth.

https://openlibrary.org/books/OL7052737M/Audels_Engineers_and_Mechanics_Guide_1

I have constructed Bilgram diagrams for several Shays, all the model designs I have plans for and a few others like the Ripper launch. This is the very first time I have made a Bilgram diagram for an engine that I did not have a full set of plans for. It has occurred to me that with a full plan set there is no real reason to learn about a Bilgram diagram. I was a Marine Engineer by trade and am curious about mechanical things and the more you know about the main engine of the ship you are on the better you will be prepared when all the alarms go off and the light to your cabin did not come on. I have had to make decisions and give orders on the fly with limited information. Learning about an engine on the design level is a large part of the enjoyment I have building model engines. I have checked the library collections of most of the major engineering universities in the US and I have the same books that were used for teaching about steam engines and slide valves on my shelf in my drafting office.

Back to where this left off with port width and port opening. I set port opening equal to port simply as a starting point of this discussion. All the valve terms I am using are defined in the Audels book in chapter 4 see pages 179-210. On page 203 the first question on the page is “Ques. What is the relationship between the port opening and the port width? Ans. It may be either greater or less than the width of the port,” well dang it seems that they forgot to mention the condition of equal port opening and width. The term over travel is defined as the valve traveling past the full open position. It is no surprise that the term under travel is defined as the steam port not fully opening. I will get back to this topic after the valve is completely drawn.

The book gives the main dimensions of the engine used to construct a Bilgram diagram.

              “Example.—A 7-7 engine is to run at 450 revolutions per minute. What are the principal dimensions of the slide valve and ports for a steam velocity of 8,000 feet per minute through the port opening and 6,000 feet through the ports? Lead 1/16 inch, cut off Ÿ, release .9 stroke, length of ports .8 the diameter of the cylinder. And length of connecting rod 2 œ times the stroke.”

The engine has a short connecting rod so it is most likely a vertical engine. If we changed the release to full stroke with no inside lap and slowed the engine to 300 rpm it would be a very good description of the early Shay engine with two 7” x 7” cylinders. They used the steam velocity with the rest of the data to calculate a port opening. This is the way to go when designing a full size engine.

There are several strategies for model builders to determine what to use for port width.

(1)    Full size plans can be scaled down.

(2)    Model plans with a similar size cylinder can be used The book “Manual of Model Locomotive Construction” by Martin Evans has a list of cylinder sizes with port dimensions.

(3)    The width of the bridge or the section of the valve face between the steam port and the exhaust port is a casting decision. The bridge is usually made the same thickness as the cylinder walls so the metal will flow and cool at the same rate. It is also very common to have the steam port width the same as the bridge width. The final piece of the puzzle is the exhaust width which is generally twice the steam port width.

Here is a drawing that shows port opening equal to port width. The valve is at the lowest point of travel and just about to start traveling up and the width of the bridge is equal to the width of the steam port. The letters may seem random but they match the named edges in the Audels sample problem. I will be using the same terms that have been defined in chapter 4. The letters are not really necessary I am simply using them to match the example in the book.



Cheers Dan

[Dan Rowe]

I am working out how to use a Bilgram diagram with a piston valve. It should be simple because the change between piston valves and D slide valves is just flip the eccentrics 180. Now that sounds like that would reverse the engine and that is correct. In order to show a D slide valve and a piston valve using the same Bilgram diagram one is going in one direction and the other is going in the opposite direction.

Chris asked me if Bilgram would predict what happens when the reverse lever is notched back with Stephenson gear. My answer was no it will not. I got long winded and mentioned crossed and open eccentric rods. The difference between open and crossed rods is flipping the eccentric. To read about what happens with this switch read the section in Audels on this subject. Page 322. This is really about Stephenson linkage and we are talking about valves in this thread, but one more factor comes into play and that is direct and indirect Stephenson valve gear. Direct is like a marine engine or a Shay locomotive. Indirect Stephenson uses a rocker shaft like a rod locomotive.

Okay, Blah Blah Blah.... time for the graphics department to the rescue. Here is a drawing lifted almost directly from Don Ashton's book "Stephenson Valve Gear for Model Engineers". The first page is the preferred arrangement for less dieslip with launch and 'locomotive or marine links'. The difference between 'marine or naval' links and locomotive links is locomotive links are made with a flat plate with a radius slot, and marine links are made from a set of curved bars.



This second page is the less preferred arrangements that have more dieslip and require more compensation.



Now to close this by throwing yet another monkey wrench at it.....ALL the drawings are shown with the most common arrangement which is open rods. To change them to crossed rods simply flip the crank pin 180 degrees.

Man I hope that cleared this up. It is all the possibilities of the eccentric orientation for open rods. It is left to the reader to work out what crossing the rods will do to the valve linkage.

Cheers Dan

[crueby]

Um, you show d valve shapes as inside admission and piston as outside, but piston valves can be either with the same shape, just different passages around them... On the Sabino the piston valves are one of each, with the exact same valve shape.




After this thread wraps up, we need to show the double d valves like Marion used with reversing and throttle built in, and are inside admission with outside help... But thats another whole discussion!

[Dan Rowe]

Chris yes I know that now but that is the first INSIDE admission piston valve I have ever seen. I have never seen one mentioned in any valve gear book the assumption Don Ashton makes is ALL piston valves are outside admission as he did not label them.

If I had started with the LP valve with outside admission the graphics would be much simpler as it works exactly like a D slide valve.

Cheers Dan

[crueby]

Chris yes I know that now but that is the first INSIDE admission piston valve I have ever seen. I have never seen one mentioned in any valve gear book the assumption Don Ashton makes is ALL piston valves are outside admission as he did not label them.

If I had started with the LP valve with outside admission the graphics would be much simpler as it works exactly like a D slide valve.

Cheers Dan

Interesting. The Stanley piston valves (which were experimental, not in normal production by them) were inside admission too. The first place I remember seeing inside admission piston valves was in a description of locomotive valves - don't remember where though, years ago.


Just looking at the Audel book that you gave the link to earlier. One thing you had mentioned about the Stephenson links is that you thought the statement by George King's book where he gave the cutoff as 30 percent of the stroke would not be right - in Audel he states just past page 322 that 25 percent of the stroke was do-able if the port opening was greater than the port width. That gives me a clue as to the ports on the real Sabino engine - thats one thing that I don't have direct measurements on since I couldn't dismantle the engine, all I have are eccentric throws and piston valve sizes, and I was assuming the normal arrangement I've seen in the past - may have to rethink that on my design!

[crueby]

... (snip) ...

Man I hope that cleared this up. It is all the possibilities of the eccentric orientation for open rods. It is left to the reader to work out what crossing the rods will do to the valve linkage.

Cheers Dan

Hi Dan,
This reminds me of a pet peeve from my (long ago) school days, when I'd pick up a textbook for a subject that I was not taking a class for, and wanted to self-teach on. This is NOT a criticism of you, you are doing a great job answering questions! Its when there is no teacher or author around that its a huge problem. When seeing a statement like that, and I was not able to figure out the 'left to the reader' part, and there was no one to ask questions of, that I'd get royally swarfed off and want to stuff a hungry/angry shop gnome in the authors, um, toolbox!   
Sorry, just needed to vent that one! Back to the great thread!
Chris

[Charles Lamont]

The vast majority of piston valve locomotives have inside admission. It means the gland is subject only to exhaust back pressure. Straight, direct ports to minimise the clearance volume mean the valve chamber extends well beyond the cylinder covers. This also maximises the distance, and steam volume, between the valve heads.

[steamer]

Don't know if it was mentioned, but Sabino is inside admission on the HP and outside on the LP

[Dan Rowe]

Don't know if it was mentioned, but Sabino is inside admission on the HP and outside on the LP

Dave yep Chris pointed that out after looking at the eccentric diagrams I borrowed from Don Ashton.  I knew this was the case which is why I made the label on the piston valve to indicate outside admission.

To use the diagrams simply remember that an inside admission piston valve behaves EXACTLY like a D slide valve.

Cheers Dan

[Dan Rowe]

I have to give thanks to Charles for making me open a few of my valve gear books to find out just how wrong my impression that piston valves are just outside admission. I found a lot more information about inside admission piston valves that I could locate about outside admission piston valves.

I have always been laser focused on Stephenson valve gear and I think I should have read a bit widely in the valve gear books I own. A telling case is D.L Ashtons book “Walshchaerts Valve Gear for Model Engineers”. This book is really about both Stephenson and Walschaerts valve gear and the first three pages are for both types of valve gear.
 

Note that both valves do not have exhaust lap. Ashton states that is is very small in most cases and will not make much difference in a model engine. For the Sabino running on air all bets are off as to cutoff as air expansion is tiny compared to steam which is what the model wil be run on.
 
Page 2 of the Walschaerts half of the book is describing a 5” gauge loco. Here is a v very helpful quote:

“Since the passageways then to pass a high volume of low pressure steam their proportions should be adequate, (.156 & 0.187) and when they will cope with the exhaust they can more than adequately cope with the small amount of high pressure steam required at inlet.

For this reason it is rarely necessary to open the port at inlet much more than about threequarters of its width, so in dealing with valve gears we must distinguish quite clearly between port opening and port width – the width is fixed at the cylinder, but the opening depends on valve travel. Beware, since some information sources fail to make a distinction.”

Now a quote from “Locomotive Valves and Valve Gears” by Yoder and Wharen. Yoder worked for the Pennsylvania RR as the Supervisor, Apprentices, and Wharen was a professor of mechanical engineering at the University of Pennsylvania.

Page 251

“The D slide valve is always arranged for outside admission. The piston valve may be arranged for either outside or inside admission. As already pointed out the piston valve with inside admission has a number of advantages, prominent among these is the absence of live steam at the ends of the valve chamber where it is more readily condensed, and also the absence of high pressure upon the valve stem packing. With this arrangement the valve is more readily balanced. The inside admission piston valve also permits the steam passages to the cylinder to be made very short and direct. For these reasons the inside admission piston valve is preferred to the outside admission style and is used in nearly all cases.”

Somewhat in defense of my lack of interest in piston valves is I only own 2 G1 locos that should have piston valves. One of these is the last Shay built S/N 3354 WM #6. I just checked the model with the Ashton graphic of all the open rod Stephenson gear setups and guess what the #6 has inside admission piston valves.

The other model is the SP GS4 Daylight with Walschaerts valve gear. Now the real drawback of piston valves for a model engine especially in the smaller sizes where working cylinder drain cocks are rarely fitted is condensation caused by warming up the cylinders at the start of a run. A D slide valve can lift off the seat and let the water pass with little trouble, but a piston valve can not lift off the valve seat and it will cause hydraulic lock. I did say that this engine should have piston valves but it really has a D slide valve. In order to make the linkage look correct, a port reverser plate was fitted below the D slide valve to make it work like an inside admission piston valve.

Knowing from Charles that outside admission piston valves are rare the first book I checked was a small red volume by W.W. Wood an air brake inspector titled “The Walschaert Locomotive Gear”(1906.) I have to say that If any reader is interested in the study of Walschaert valve gear that this is the volume to search for. DO not be tempted to purchase a reprint of the work as there is a secret pocket in the front that has two paper cut out valves one for inside admission and one for outside admission. These act as a partial model to help visualize what is happening as the valve moves. After a bit of careful reading and finding a bunch of interesting facts about the gear I hit pay dirt.

It seems like William Mason owner of the Mason Machine Company was one of the early American adopters of Walschaerts valve gear in the 1870’s. Several 0-6-0 locomotives are identical to the illustration on page 53. These locomotives had D slide valves. The author states that the line where he received his early RR training had one of the batch and the locomotives performance was legendary.

Now for a telling quote starting at the bottom of page 57:

              “Up to this point we have considered the Walscheart gear in connection with outside admission slide valves, while as a mater of fact, at this date the majority of American locomotives equipped with Wachaert’s device have inside admission piston valves, the builders, or purchasers, not taking the hint from European practice that the D slide valve may be a component part of the Walshaert theory”

Wood was not complementary to the use of outside admission with Walschaert gear to say the very least.

So It seems that the American practice with Walshaert gear was the exception to the rule for outside admission piston valves.

Cheers Dan

[crueby]

Yup - that ol' dog just learned a new trick!       I see, I see more diagrams in your future...!   

[Dan Rowe]

I see, I see more diagrams in your future...!   

Yes Chris, but the graphics department of the loco works is talking about a walkout if this thread does not have a finished outside admission piston valve solution soon. 

Cheers Dan

[crueby]

I see, I see more diagrams in your future...!   

Yes Chris, but the graphics department of the loco works is talking about a walkout if this thread does not have a finished outside admission piston valve solution soon. 

Cheers Dan

The art department needs a box of Oreos...

[Dan Rowe]

Chris, the only Shay piston valve drawing I have on hand was for the first Shay equipped with piston valves. A very odd thing about this unique loco was that the #1 cylinder (closest to the engineer) had a D slide valve and the other 2 cylinders had piston valves. I think it used the standard crankshaft for a 3-12" x 14" so the #1 and #3  eccentrics must have been a mirror of each other. I have to check the drawings after this thread winds down to see if the piston valves were inside admission as I am now suspecting them to be.

I just checked on Shaylocomotive.com and this FACT is not recorded. It looks like someone failed to mention it when I was working on the book. I was planning to draw S/N 591 for the class C Shay. I did drawings for all the other classes including the first four truck model S/N 673.

I found an interesting artifact on the frame drawings for S/N 673 there was a hole for a rivet that was half a hole off from the matching part. If both parts were made to the drawing then someone was going to have to get out the big reamer to make the hole oversize for a custom larger rivet. A bad day on the Lima Shop floor sometime in 1907.

Tales from the Shay drafting room in Dripping Springs TX.

Cheers Dan

[Dan Rowe]

After this thread wraps up, we need to show the double d valves like Marion used with reversing and throttle built in, and are inside admission with outside help... But thats another whole discussion!

`

Hi Chris, just now responding to this, yes a thread on double D valves... The early Shays were equipped with a double D valve. They can be seen in a clear photo of the steam chest because the steam chest extends past the top of the cylinder cover. I did a drawing of the 10" x10" cylinder but never tracked down the slide valves which undoubtedly have outside lap.

The double D slide valve is I believe a variation of the long slide valve invented by William Murdock I found the British patent number and the date but I never found how to find a copy of the patent online. Maybe there is someone familiar with online British patents reading this who can supply a link for the research.

Cheers Dan

[crueby]

Dan, send me the British patent number, I can look that up. I have the Marion patent on how they configured the double d valve, in combination with a variable opening piston valve. Fascinating, will post diagrams of that when we get there. SO many varieties of valves!!

[PJPickard]

How odd...a mix of D valves and piston valves. It's like Lima wasn't sure of the piston valves..."let's keep one a slide valve just to be on the safe side"! Hahahaha!!

[Dan Rowe]

Chris,
British Patent number 2340 in 1799. The Murdock slide valve is referred to the long slide valve in some early texts, which is what makes me think early double D variant is what is in the patent.

Cheers Dan

[Dan Rowe]

How odd...a mix of D valves and piston valves. It's like Lima wasn't sure of the piston valves..."let's keep one a slide valve just to be on the safe side"! Hahahaha!!

Paul, you might have something there as it really is a mystery. The drawings for the D slide valve cylinder are on a separate cylinder drawing and I got the impression that it was a last minute change so I have to check the drawing dates when I pull them from the stack.

There is also a field report for this engine if I can find where I stashed it on my hard drive.

Cheers Dan

[crueby]

How odd...a mix of D valves and piston valves. It's like Lima wasn't sure of the piston valves..."let's keep one a slide valve just to be on the safe side"! Hahahaha!!

Its very common for Corliss valve compounds to have poppet valves on the LP cylinder inlet/exhaust and sometimes the IP exhaust too, by that point they are just trying to get the most flow through with the lower pressure steam. Piston and D valves are an unusual combination though.

[crueby]

Chris,
British Patent number 2340 in 1799. The Murdock slide valve is referred to the long slide valve in some early texts, which is what makes me think early double D variant is what is in the patent.

Cheers Dan

Hi Dan,
Found it - they way they represent the patent numbers of those early ones is 'GB' then the year, then the number with zeros to pad it out to 9 digits, then A.  So, "GB179902340A". I've attached a copy of the original patent in PDF form for you.
Chris

[Dan Rowe]

Chris, no such thing as a Shay compound. I wish that was not the case. The #1 cylinder on S/N 591 was an HP cylinder exactly like #2 & #3 all HP steam to a common steam bracket that functioned as HP steam supply for each cylinder and separate exhaust passages to the common exhaust pipe.

Cheers Dan

[Dan Rowe]

Hi Dan,
Found it - they way they represent the patent numbers of those early ones is 'GB' then the year, then the number with zeros to pad it out to 9 digits, then A.  So, "GB179902340A". I've attached a copy of the original patent in PDF form for you.
Chris

Wow thanks, Chris now that I see the drawings I have seen some of them but not all of them. I will have to READ the words and work out how the very first slide valve worked.

very cool......

Cheers Dan

[crueby]

Hi Dan,
Found it - they way they represent the patent numbers of those early ones is 'GB' then the year, then the number with zeros to pad it out to 9 digits, then A.  So, "GB179902340A". I've attached a copy of the original patent in PDF form for you.
Chris

Wow thanks, Chris now that I see the drawings I have seen some of them but not all of them. I will have to READ the words and work out how the very first slide valve worked.

very cool......

Cheers Dan

You're welcome!  Patents are an amazing resource, since they talk about what the invention is, how it works, and how it is (supposedly) better than what came before it.
 

[Dan Rowe]

they way they represent the patent numbers of those early ones is 'GB' then the year, then the number with zeros to pad it out to 9 digits, then A.  So, "GB179902340A".

Chris thanks for that formula. I knew the date was important for early GB patents just not the code to convert it to a usable patent number.

Cheers Dan

[MJM460]

Hi Dan, A very interesting thread.  I like that Bilgram diagram.  I have not seen it before, but it seems more straight forward than the others I am aware of.

 You have clearly put a lot of time into the study of valve gears.  Thanks for taking the time to write it up.

Interesting that Sabina had inside admission at the HP end and outside admission at the LP end.  I suggest that the difference comes from consideration of packing leakage in each case.  Putting the lower pressure makes sense at the HP end as already mentioned, and also helps with valve balance as the LP on the rod area leaves a lower unbalanced force.

At the LP end of a condensing engine, the issue is air leakage in through the packing due to the condenser vacuum.  This air all has to be removed by the air pump, and reduces the vacuum due to its effect on the condensing temperature.  So similar consideration, gland leakage, leads to a different solution in each case.

MJM460

[Dan Rowe]

You have clearly put a lot of time into the study of valve gears.  Thanks for taking the time to write it up.

At the LP end of a condensing engine, the issue is air leakage in through the packing due to the condenser vacuum. 

Hi MJM, thanks for stopping by, and yes I have spent a fair amount of time studying valve gears. As Chris mentioned without a teacher or even answers in the back of the book, it is very difficult to master a subject. I am still learning new things mainly because I am taking the time to write this up and have knowledgeable folks read it and ask questions or point out errors in my understanding of the subject.

The only reversing valve gear that I have spent much time with is Stephenson valve gear. I need to do a refresher on that subject to finalize the model designs for two Shay engines. I will be explaining the graphical method to correct for the angularity of the rods by finding the optimum location for the suspension point of the link. This is covered in Don Ashton's book but it uses an Excel spreadsheet with an add on called solver. I never worked out how to get the answer with the spreadsheet but I did a Shay design for a fellow Shay fan and he got in touch with Don Ashton to work the problem with the spreadsheet. I got the very same EXACT answer. A graphical solution using cad is just as accurate as a spreadsheet and it might not be as simple as a plug and chug solution, but I like the ability to visualize the math with a drawing.

Now that you mention the vacuum on the LP cylinder I realize that this must be the main reason that many of the marine engines have D slide valves for the LP cylinder. Now if it has a piston valve I know to check for outside admission.

Cheers Dan

[Dan Rowe]

Here is the piston valve with the D slide valve. I used P. 214 in Audels book for the procedure and the numbers from the Bilgram diagram. I originally thought that the steam lap for the piston valve should be on the inside because it is inside admission, but this did not work at all on the drafting board. After a lot of tries and fails I switched the steam lap to the outside just like the D slide valve and that worked, so much for logic. Here are both valves in the mid-travel position.



The port opening and the port width were set equal and the bridge on the D slide valve is also equal to the port width. I also set the middle port for the piston valve equal to port width so both ports on the piston valve are the same size. Here are both valves at full travel.



Looking at the drawings both valves have the same size path at extreme travel.

The main difference in the valves is one should be traveling up while the other one is traveling down. Both valves are symmetrical to the centerline so if we turn one over just simply think it is going the other direction. I think the piston valve works fine for both outside admission and inside admission, so no need to draw both valves for the Sabino, which has an outside admission valve for the HP cylinder and an outside admission valve for the LP cylinder.

The final part of this discussion will be about the merits of using over travel or under travel.

Cheers Dan

[crueby]

Hi Dan,
One issue I see with the way you drew the piston valve side. For inside admission, the port H is the steam inlet, the outside ends of the piston are the exhaust. As drawn, the piston valve is so long that the exhaust is not being opened till after the port at the inlet end is opened, which would mean that the exhaust end of the cylinder would not be opened till well after the piston in the cylinder was on its way down, causing back pressure and possibly stalling the engine. The cause is the fact that you moved the steam lap to the outside - that is where the exhaust is on inside admission so you actually introduced exhaust lap. If you compare the piston valve side of the drawings to the slide valve side, the distance from A to F on the slide valve is the steam lap - the distance from B to F on the piston valve should be that same distance.

Oh, and the steam inlet passage for the piston valve version, H in your drawing, is usually larger, since you want free flow in to the center area of the piston valve. Not that important for these drawings, since that passage is never covered. Of more import is the diameter of the ends of the valve vs the diameter of the center post, since that controls the volume that the steam can flow from the inlet to the port to the cylinder. Typically the ends are several times the diameter of the post.

Chris

[steamer]

Inside on the HP is simple    it keeps high pressure steam away from the valve gland.   In marine compounds/ triples  the LP is usually outside admission to keep vacuum away from the glands     low pressure wet steam lubricates packing very well.

[Dan Rowe]

Hi Chris, yes I see your point. I drew it the other way the first time and something did not work right that way. I forget what it was as my brain went to meltdown about an hour ago. I will put the outside lap back on the outside tomorrow and take a fresh look then.

This was the first piston valve I have drawn with a Bilgram diagram, it would have been nice to get it correct on the first try, but no joy 

Yes, Dave, it should have been simple I am fairly sure I made an obvious goof swapping the lap, I can not remember why I did not like it the other way a new drawing tomorrow and hopefully, I will spot the issue or it will just work.

Cheers Dan

[Dan Rowe]

As drawn, the piston valve is so long

Yes, Chris, it would have been simple the first time if I could have simply made the valve shorter, but I have to stick with the valve length you gave me.

Well, that should work for the LP cylinder, so I get a second try on the HP tomorrow.

Cheers Dan

[crueby]

As drawn, the piston valve is so long

Yes, Chris, it would have been simple the first time if I could have simply made the valve shorter, but I have to stick with the valve length you gave me.

Well, that should work for the LP cylinder, so I get a second try on the HP tomorrow.

Cheers Dan

Hmmm, I phrased that badly - what I meant was the length of the valve end (green arrows) in relation to the port it is covering (blue arrows):


You are adding more lap than I had drawn, which is the point of the whole diagrams, I get that, its just that it should have been added on the inside of the valve rather than the outside. Sorry for the confusion, I should have drawn a picture, then even I would have followed what I was trying to say!   

[Dan Rowe]

Hi Chris, no you did not really confuse me I was already there and then some.

I worked it out and it is a simple change to get the HP from the LP I drew. Move the ports away from each other to make the small lap on the outside like it should be.

If you change the size of the pistons on the valve you are not using the numbers on the Bilgram diagram so the cutoff would change.

I will have the drawing tomorrow but the numbers on the Bilgram will work if you just have to drill some holes in metal.

Note to self:....put the distance between the ports on the diagram so Chris can cut metal soon.

Cheers Dan

[crueby]

Great that it's going to come together. I'm still a ways from cutting ports and cylinders, need to do the crossheads, after that may be time to start roughing out the two cylinder blocks and thier mounting plates, lots to do there. The reverse gear was going to be next instead, but I think it may be easier to be able to work from the valve rids down so the parts have something to hang from. The curves in the follower arms and the shapes of the clevises are complex, so being able to have both ends to fit to would help. Bottom line, will be a couple weeks at least till the ports need to be finalized on paper, probably at least a month given summer travel season is coming!

[Dan Rowe]

Hi Chris,
This thread has brought a bunch of facts about piston valves to my attention so it has been fun learning new stuff from books that were published 90 to well over one hundred years ago. I will have time to write the conclusion of this study soon to reinforce the new concepts that were brought out by this open to the world discussion.

I have to draw the double barn door I am installing on the master bath. One of the instructions was to cut a 7mm by 22mm grove in the bottom of the door with a CHAINSAW


WoW, that is the worst idea I have ever seen in an instruction manual and the most dangerous. It makes me not trust anything in the instructions. That is why it is on my drafting board. Doing things twice is a real drag.

Cheers Dan

[crueby]

Barn doors on the master bath...  Cows or horses need to get in there?  Guess things really ARE different in Texas... 

[Dan Rowe]

Yes Chris, things are indeed different in Texas. The State Capital building in Austin only about 40 miles from here has two large doors big enough for a horse and rider and it has been tested for a fact. As in you and the horse you rode in with.

I was thinking more like wheelchair access as the overhead is not large enough for the horses.

Cheers Dan

[crueby]

Yes Chris, things are indeed different in Texas. The State Capital building in Austin only about 40 miles from here has two large doors big enough for a horse and rider and it has been tested for a fact. As in you and the horse you rode in with.

I was thinking more like wheelchair access as the overhead is not large enough for the horses.

Cheers Dan

Wow, they make wheelchairs for horses down there.... Who'da thunk it!   

[Dan Rowe]

Hi Chris, I just posted this on the Sabino thread and it really belongs with this thread:

The main record for any Shay has the angle of advance and the valve travel on the first page. This not only gives key dimensions for the eccentric casting it is enough to make a Bilgram diagram with only one more fact that the lead is 1/16".

I have worked a bunch of Bilgram diagrams for Shay engines. Here is the secret the lead is not really 1/16" but only fairly close. The valve travel and the angle of advance, and the lap distance are whole numbers with fractions. To make that come out exactly the lead is the fudge factor.

Now time for the pop quiz.
Someone give me a number between 200 and 2999.
I will take that shop number and list the angle of advance and valve travel.

Then I will make a Bilgram diagram to show the cutoff only knowing that the lead is approximately 1/16".

Cheers Dan

[Dan Rowe]

I picked a number, 5048. That is not a Shop number it is a slide valve drawing number. I chose that one because it says to refer back to CD #3. I know that card very well it is an early Shay drawing with complete details for 8" x 8" Shay cylinders.

Now to the file cabinet to get the folder for 2- 8" x 8" Shays. the first one in the folder is shop number 50.

Valve Travel 1 1/2"
Angular Advance 22⁰

Now I will draw the Bilgram diagram with approximately 1/16" lead.

Thanks for playing 'Stump the Chump'.

Cheers Dan

[crueby]

I was tempted to pick something like 123.567 since you didn't specify a whole number...   




Looking forward to seeing the diagram.   

[Dan Rowe]

Chris, that number is below 200 so no brass ring for you 

  Bilgram hot off the press!!!!!!!

Valve travel 1.5
Angle of advance 22⁰
Lap .25
Lead .031
Cutoff 1.312/1.5 = 0.875
Port opening 0.5

I believe that port opening is equal to port width. I will have to check card #3 tomorrow to see.
Not bad information for two numbers and an approximate lead.

Cheers Dan

[crueby]

Okay, thats a very interesting diagram, now I'm finally getting to visualize how changing one parameter would ripple through the other ones.  It would be interesting (as well) to draw the resulting ports and valve to scale with those numbers and see what the parts would look like - thats the direction I have been coming from (since I didn't know this type of design tool).

Seems like it would be possible to code this all up in a spreadsheet, and have it take the design parameters in and do the drawing for you? That would allow for playing with the lead/lap/advance/throw/etc and see the results, to help wade through all the design possiblities.

 I've seen that sort of thing done, but have never gotten that deep into line drawing/chart drawing in spreadsheets. I could dust off my C++ compilers and libraries and do it that way, but thats not very portable for sharing with others. Maybe even code it in PostScript to generate a PDF picture. HTML and have a page for a web browser? Hmmm. Must be a good tool for that - don't have MatLab any more, that would do it in about 20 characters of incomprehensible but powerful code...  GCode that would print it or CNC it on a plate?!      Uh-Oh, my past life as a software geek is leaking out!!   

Edit: What does the distance 0.281 represent again?

[Dan Rowe]

Okay, thats a very interesting diagram, now I'm finally getting to visualize how changing one parameter would ripple through the other ones.  It would be interesting (as well) to draw the resulting ports and valve to scale with those numbers and see what the parts would look like - thats the direction I have been coming from (since I didn't know this type of design tool).

Edit: What does the distance 0.281 represent again?

Chris, you hit the nail on the head. That is the reason that Bilgram is so powerful-------it is visual. Don't make the mistake of hiding the visual math in a spreadsheet.

I knew the lead was approximately 1/16" so I drew a line from the end of the angle of advance to the flag pole. That is 0.281 and the nearest fraction is 1/4".

Case closed for shop number 50. I just have to check the answers on card #3. The first thing I will check is the length of the valve found on card 952-A-5048 which is 4 11/32" against the distance between the steam port outer limits. It should b 0.5" longer or twice the lap.

Cheers Dan

[crueby]

The idea of the spreadsheet I had was to speed up trying different parameters, having the code draw the diagram so its still visual, just quicker to see what happens if I went to a longer or shorter lead, or whatever. Just a timesaver but still ending with the same diagram. Just a thought!

[Dan Rowe]

Seems like it would be possible to code this all up in a spreadsheet, and have it take the design parameters in and do the drawing for you? That would allow for playing with the lead/lap/advance/throw/etc and see the results, to help wade through all the design possiblities.

 I've seen that sort of thing done, but have never gotten that deep into line drawing/chart drawing in spreadsheets. I could dust off my C++ compilers and libraries and do it that way, but thats not very portable for sharing with others. Maybe even code it in PostScript to generate a PDF picture. HTML and have a page for a web browser? Hmmm. Must be a good tool for that - don't have MatLab any more, that would do it in about 20 characters of incomprehensible but powerful code...  GCode that would print it or CNC it on a plate?!      Uh-Oh, my past life as a software geek is leaking out!!   

Edit: What does the distance 0.281 represent again?

Hi Chris, yes if you know how to code any program to do this it would be great. Something stand alone or on the web so others could use it with the normal software on a computer would be fantastic. I think that if it was like Docksteader's Zeuner module it would be very handy. If the program could start the construction with only 3 key variables it would be even better.

It is not really hard to construct a Bilgram diagram but to do multiple constructions to see 'what if' could get a bit tedious.

A better answer to "What does the distance 0.281 represent?" is it is the linear advance. This is shown in Audels Fig. 388 Pg 213. Now to the answer to the question "What is linear advance?" see Fig.387 Pg. 206. to see that linear advance equals lap plus lead. So we can add linear advance to the things we learned from the Bilgram diagram for S/N 50.

I mentioned one fact found on the slide valve drawing I cherry picked out of the drawing drawer but there are a few more dimensions that will be useful for this slide valve design.

I mentioned that the outside width of the valve is 4 11/32", the inside exhaust cavity is 2 1/2" wide, the outside length of the valve is 7 63/64", and the inside length is 7". The card number is 7404 and the superseded card is 942-A-5048. This valve was used for 8" x 8', 9" x 8", 8" x 12" and 8" x 10", so I could have picked several Shay engines to make the Bilgram diagram for. The note "REFER BACK TO CD. #3." is what made me pick that valve on the card with 8 different slide valves on it.

So without peeking at the answer sheet card #3 what else do we know about the valve design of S/N 50? To start I have to make some assumptions:
1. Port opening equals port width and bridge width.
2. Inside lap is equal to zero.
3. The width of the port is equal to the width of the bridge.
4. At the end of the valve travel, the outer edge of the valve completely opens the valve no more no less, so we do not have over travel or under travel. Port opening is a confusing name. If we look at the angle of advance line it is clear that port opening plus lap is equal to 1/2 the valve travel. By saying port opening is equal to port width when the valve travels the port width then travels the lap distance, it should be clear that that distance traveled is equal to 1/2 the valve travel.

Wow, that was a lot of beating around the bush but I really hope that it made the difference between port opening and port width a bit more clear. This is also covered in the book on Pg. 205.

Okay, the valve inside length is 7", so Pg. 184 the length of the ports are usually 0.8 times the diameter of the cylinder. Cylinder bore 8" times 0.8 equals 6.4, so a bit shy of 7" which has to be the dimension on card #3.

Assumption #2, no inside lap makes the width of the exhaust port the same as the inside width of the valve or 2 1/2".

The distance between the valve face steam edges is the valve outside width minus twice the lap or 4 11/32 - 1/2" = 3 27/32".

Port width = port opening = bridge width = 1/2".

Now, this should all add up. to 2 x port width + 2 x lap + 2 x bridge width +exhaust width = total valve length.

1 + 0.5 + 1 + 2.5" = 4" which leaves us 11/32" short. That means that we have inside lap or the bridge width is not 1/2" or a bit of both. The port opening might not equal the port width, so it looks like assumptions 1 & 2 need to be checked for truth.

Well, that is all I can think of that we know from the Bilgram diagram and a few assumptions. Time to check the answer sheet card #3.

Cheers Dan

I think I finished the edits to this so now to pull card #3 for real.

[Dan Rowe]

  well dang so much for card #3 it has every engine part on a single sheet EXCEPT for the cylinder.

Now I have to find card 108 for the 8" x 8" cylinder or card 138 for the 9" x 8" cylinder. I never finished putting all the drawings back in the proper drawers after my last reorganization and I am paying the price for that bad decision.

Cheers Dan

[crueby]

Turn off the fan and close the window so it doesn't blow the papers around and mix them up more!!

[Dan Rowe]

Hi Chris, it is going to take a very strong fan to get that stack o paper moving. It is close to 3/4" of mostly C size sheets with the cranks which are all special sizes.



The top sheet is 7404 which is a slide valve group card. I checked the slide valve on card #3 and the outside width is not the same card #3 says 4 3/8" and card 7404 set 3 says 4 11/32". The angle of advance has to be different for the two versions of the 8" x 8" valve and I will be able to spot the change in the records.

It looks like port opening does not equal port width, and there is inside lap.

I have drawn this engine before I just have to locate the drawings. I drew it for the article I wrote about Bilgram's diagram for "Steam in the Garden". I think the article used the shorter version of the valve.

I will post the article and show the valve design tomorrow and talk about over and under travel. Kozo used over travel and he said why when he built the second Shay. Does anyone remember his logic?

Cheers Dan

[crueby]

I didn't remember anything about overtravel on his New Shay, so just checked the book, couldn't see any mention of that....

[Dan Rowe]

Chris, I am not sure where it is in the book but I would guess near the Zeuner diagram. I think it was something like 0.5mm over travel to compensate for pin wear so the valve will still fully open with some pin slop. I had wondered about that for years so it made an impact on me something like a hammer. WhamO.

Cheers Dan