Author Topic: Port areas  (Read 5068 times)

Offline Bikerbob

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Port areas
« 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
Bikerbob

Offline b.lindsey

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Re: Port areas
« Reply #1 on: April 26, 2016, 03:03:09 PM »
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

Offline Bikerbob

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Re: Port areas
« Reply #2 on: April 26, 2016, 05:42:19 PM »
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]
Bikerbob

Offline Jasonb

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Re: Port areas
« Reply #3 on: April 26, 2016, 05:49:58 PM »
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

Offline steamer

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Re: Port areas
« Reply #4 on: April 26, 2016, 05:56:47 PM »
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
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Offline steamer

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Re: Port areas
« Reply #5 on: April 26, 2016, 07:40:35 PM »
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
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Dan Rowe

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Re: Port areas
« Reply #6 on: April 26, 2016, 08:49:09 PM »
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
ShaylocoDan

Offline steamer

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Re: Port areas
« Reply #7 on: April 26, 2016, 08:55:26 PM »
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!
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Jasonb

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Re: Port areas
« Reply #8 on: April 26, 2016, 09:00:49 PM »
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

Offline steamer

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Re: Port areas
« Reply #9 on: April 26, 2016, 09:13:03 PM »
Just trying to teach it correctly Jason.

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Bikerbob

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Re: Port areas
« Reply #10 on: April 27, 2016, 03:25:47 PM »
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
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Offline Bikerbob

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Re: Port areas
« Reply #11 on: April 27, 2016, 03:28:26 PM »
Jasonb
Thanks for the info; hope to put it to physical use shortly
Bikerbob
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Offline Bikerbob

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Re: Port areas
« Reply #12 on: April 27, 2016, 03:32:17 PM »
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
Bikerbob

Offline Dan Rowe

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Re: Port areas
« Reply #13 on: April 27, 2016, 03:42:12 PM »
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
ShaylocoDan

Offline Maryak

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Re: Port areas
« Reply #14 on: April 27, 2016, 10:37:32 PM »
Hi Bob,

Attached Excel file for Steam Port Area.

HTH
Another Bob
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