Author Topic: Bilgram's valve diagram a graphical method to design a steam valve  (Read 7384 times)

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #15 on: April 12, 2022, 06:59:46 PM »
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
« Last Edit: April 12, 2022, 09:29:12 PM by Dan Rowe »
ShaylocoDan

Offline Zephyrin

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #16 on: April 13, 2022, 10:25:46 AM »

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.

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #17 on: April 13, 2022, 04:15:36 PM »
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

ShaylocoDan

Offline Zephyrin

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #18 on: April 13, 2022, 05:01:22 PM »
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...

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #19 on: April 14, 2022, 07:13:37 PM »
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
ShaylocoDan

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #20 on: April 16, 2022, 12:00:16 AM »
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 ¾, release .9 stroke, length of ports .8 the diameter of the cylinder. And length of connecting rod 2 ½ 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

« Last Edit: April 16, 2022, 12:17:20 AM by Dan Rowe »
ShaylocoDan

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #21 on: April 16, 2022, 11:45:10 PM »
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
« Last Edit: April 17, 2022, 01:08:43 AM by Dan Rowe »
ShaylocoDan

Offline crueby

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #22 on: April 17, 2022, 01:20:19 AM »
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!

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #23 on: April 17, 2022, 01:30:59 AM »
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
ShaylocoDan

Offline crueby

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #24 on: April 17, 2022, 01:37:22 AM »
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!

Offline crueby

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #25 on: April 17, 2022, 02:05:00 AM »
... (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!   :LittleDevil:
Sorry, just needed to vent that one! Back to the great thread!
Chris

Offline Charles Lamont

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #26 on: April 17, 2022, 09:16:35 AM »
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.

Offline steamer

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #27 on: April 18, 2022, 12:18:34 AM »
Don't know if it was mentioned, but Sabino is inside admission on the HP and outside on the LP
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #28 on: April 18, 2022, 07:13:53 PM »
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
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Offline Dan Rowe

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Re: Bilgram's valve diagram a graphical method to design a steam valve
« Reply #29 on: April 18, 2022, 07:15:17 PM »
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
« Last Edit: April 18, 2022, 07:40:22 PM by Dan Rowe »
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