Model Engine Maker
Help! => Specific Engine Help => Topic started by: Bikerbob on April 26, 2016, 02:43:53 PM
-
Good day guys
Total newbie and attempting to draw my first steam engine 1 1/4" bore x 1" stroke. The plan I am using for reference indicates 3/16 dia steam ports; these seem large compared to other engines. Is there a rule of thumb between area of bore to port area that can be used for sizing?
Second I was going to use a "O" ring or PTFE ring on the piston; which would you recommend for operation on compressed air?
What clearance would you recommend between piston and bore?
Thank you for your attention
Bikerbob
-
Hi Bob, first off welcome to the forum though I see you have been a member for a while now. When you can, please pose an introduction in the "introduce yourself" section so more may see your interests, types of machines used, etc. to better answer your questions.
That said, 3/16" does sound a bit large even for a 1 1/4" bore. Are you talking about the ports in the steam chest though or the angled ports leading from the steam ports to both ends of the cylinder? It might help to know what you are patterning your plans after as well if possible. As for rings, PTFE is good and is normally what is supplied from such vendors as PM Research with their casting kits, though others have used O-rings successfully also. Personally I would prefer the PTFE ones. If you are only using one ring, A closer piston/bore clearance might be advisable....something like .001-.0015", allowing the ring to take up the difference. Two rings would give the piston an bit more stability though with two points of contact rather than just the one. Just my 2 cents.
Bill
-
Thank you for your reply; did some double checking to find that the true dia is 4- 3/32 dia for the ports . The reference engine is a vertical marine by C W Woodson with me adding some changes from Ray Hasbrouck designs.
Hi Bob, first off welcome to the forum though I see you have been a member for a while now. When you can, please pose an introduction in the "introduce yourself" section so more may see your interests, types of machines used, etc. to better answer your questions.
That said, 3/16" does sound a bit large even for a 1 1/4" bore. Are you talking about the ports in the steam chest though or the angled ports leading from the steam ports to both ends of the cylinder? It might help to know what you are patterning your plans after as well if possible. As for rings, PTFE is good and is normally what is supplied from such vendors as PM Research with their casting kits, though others have used O-rings successfully also. Personally I would prefer the PTFE ones. If you are only using one ring, A closer piston/bore clearance might be advisable....something like .001-.0015", allowing the ring to take up the difference. Two rings would give the piston an bit more stability though with two points of contact rather than just the one. Just my 2 cents.
Bill
[/quote]
-
Bob is this going to be an engine that will actually have to work or just one for display? Will it also have to work on steam or just air that you mention.
By way of comparrison my traction engine with a 1 3/8" bore has six 1/8" dia passages between port slots and the end of the cylinder, and that is designed to do work.
Clearances and type of ring will again depend on work/display and also piston/cylinder materials
-
Additionally, it is a direct function of the intended speed of the engine as well.
I have some data at home, I can publish some of my references ....
Dave
-
You can start your education here though
http://www.farmcollector.com/steam-traction/how-to-design-a-slide-valve.aspx
Good read and the method to determine your port area correctly discussed.
Dave
-
Dave,
Good article, thanks.
Bob, the article uses the Bilgram diagram. If you have any trouble with that diagram simply ask. It is my favorite of the valve gear graphic calculators and I can explain how it works. It is the simplest at least for me to visualize how changes affect the slide valve dimensions.
Cheers Dan
-
Dave,
Good article, thanks.
Bob, the article uses the Bilgram diagram. If you have any trouble with that diagram simply ask. It is my favorite of the valve gear graphic calculators and I can explain how it works. It is the simplest at least for me to visualize how changes affect the slide valve dimensions.
Cheers Dan
Wot Dan Said!
-
Should teh thread title really be passage sizes rather than ports sizes as teh question seems to be about passages and not port design.
Bill I gather this will just be for display running on air in which case I would stick with the four 3/32" holes, looking at the drawing they fit in fairly easily, if you are a bit worried about them wandering then three holes will do.
The last few engines I have done I have gone over toi Vitron O rings, I cut two grooves in each piston but the engines run fine with just one ring fitted.
As you will not have to worry about heat expanding teh parts I would go with 0.001 to 0.0015" smaller piston
-
Just trying to teach it correctly Jason.
Dave
-
Steamer
In the article that you referred to; it refers to fig 2; it appears that there is no fig 2 . Would you have a copy with fig 2 or another similar article you could email
Thanks
bikerbob
-
Jasonb
Thanks for the info; hope to put it to physical use shortly
Bikerbob
-
Dan Rowe
I assume the fig 2 in the article is the bilgram; when I attempt to view Fig 2 it is not there. Do you have an article on slide valve design that you could email
Thanks bikerbob
-
Bob,
Yes, I noticed on my second read that both figure 2 and figure 3 were missing, they must want you to subscribe to see the missing figures as they link to the home page.
I think that I can draw the missing figures using the text as a step by step guide. I have the lawn tractor all apart so give me a few days to work it out. I am interested in working out the approach used by Frank J. Burris for slide valve design.
Cheers Dan
-
Hi Bob,
Attached Excel file for Steam Port Area.
HTH
Another Bob
-
I located the textbook used by Frank J. Burris to write the article. It is Audels Engineers and Mechanics Guide: Volume 1, see pages 210-217. This book can be found on the web as it is out of copyright. The example in the book is nearly identical to the text by Mr. Burris he simply changed the bore and stroke of the example.
If you get stuck with this let me know.
Cheers Dan
-
You will find the fig 2 & 3 of the F Burris paper upon a click on the slideshow button !
-
Thanks Zephyrin,
Figure 2 is the Bilgram diagram and figure 3 is the slide valve. Just what i was expecting to see. I tried the slideshow button but I did not spot the arrows on the sides of figure 1.
Cheers Dan
-
BikerBob,
The Bilgram diagram is a very handy tool to lay out the port face and valve face. I can walk you through the design of this engine. The thing I need to know is the length of the connecting rod and the design cutoff as a percent of the stroke.
If you are using Jason's suggestion of 3/32" holes then we know the port opening to get the ball rolling. Most of the model designs I have looked at have 0 lead so we can ignore that. The full size Shays I study have a 1/16" lead and when that is scaled down to the scale I work in it is very tiny so I use 0 for the lead.
If you want inside lap for compression and release then we will need the design point for that which is usually 0.9 x stroke.
The steps for doing this are in the article, but to be honest, I did not understand it the first 20 or so times I read it the first time I came across it.
Cheers Dan