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Post by nightsky02 on Nov 7, 2008 15:58:36 GMT -5
Hello, I`m new to this forum and new to live steam as well.
I`ve recently completed a Kozo Switcher, and am having many difficulties.
I would greatly appreciate any help that anyone can give me regarding a few questions I have.
When I fire it up with steam, it has very little power. When I run it on compressed air, it has about 3 times more power. On steam, it wont start running with less than 75 psi. On air, it will run on as little as 25 psi.
I followed the plans pretty well, but I made the boiler out of welded steel due to copper prices.
Can anyone recommend a good, easily attainable steam oil?
Thanx
Ron Hermans
734 676 2324
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Post by siggy on Nov 7, 2008 16:51:15 GMT -5
A couple of questions - on steam does it start out running normally and then quickly degrade to the point where the large pressures are needed? Will the loco roll freely after a steam attempt? What metal did you use for the cylinders and pistons?
My questions above are related to the thought that maybe you have some tolerances in the cylinders or valves too tight. The heat from the steam may be causing differential expansion in dissimilar metals, which is leading to binding, which leads to the high pressure requirments.
If the model will still roll freely while still hot after a steam attempt then you could rule out the above. If that happens then I would probably look at the throttle or other locations in the steam plumbing lines to see if something is plugged up along that route.
Robert
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Post by Ed Hume on Nov 7, 2008 19:56:22 GMT -5
Ron,
Robert (aka Siggy) is giving you sound advice - the pistons are probably too close a fit to the cylinders. However, one other possibility is the piston packing - are you using Viton o-rings or graphite? Some kinds of o-ring materials swell up under steam.
Ed
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Post by nightsky02 on Nov 7, 2008 22:02:19 GMT -5
Thanx for your responses, Robert and Ed.
I think you both may have hit the nail on the head.
Cylinders are bronze, with aluminum pistons , and the piston seals are regular (buna N 70 durometer) o -rings.
I left a .010 diametrical clearance for the aluminum expansion, but now it occurs to me that the pistons may be heating up much faster than the cylinders. Also, I never knew about o ring swelling under steam pressure. I`ll get Viton rings and let you know how it goes. Or would graphite packings be better?
Thanx,
Ron
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Post by Ed Hume on Nov 7, 2008 22:47:55 GMT -5
Viton o-rings are preferred over graphite packing.
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Post by Harlock on Nov 8, 2008 2:23:10 GMT -5
Thanx for your responses, Robert and Ed. I think you both may have hit the nail on the head. Cylinders are bronze, with aluminum pistons , and the piston seals are regular (buna N 70 durometer) o -rings. I left a .010 diametrical clearance for the aluminum expansion, but now it occurs to me that the pistons may be heating up much faster than the cylinders. Also, I never knew about o ring swelling under steam pressure. I`ll get Viton rings and let you know how it goes. Or would graphite packings be better? Thanx, Ron I believe aluminum has a much higher coefficient of thermal expansion than bronze, so your pistons are probably expanding into the cylinders. One our members seems to be having great luck with the Viton rings. If you have any photos of your newly completed engine, we'd love to see them. --Mike P.S. we also have a special forum just for Kozo builders, livesteam.proboards23.com/index.cgi?board=kozo lots more info in there, including bench test and run videos of John's A3 with viton O rings. |
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