ivan
Member
Posts: 5
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Post by ivan on May 9, 2005 8:17:13 GMT
Can anyone tell me the received wisdom on piston valves - should they have piston rings, O rings or just rely on the fit between the bore and the valve spool. I am building a 5inch King which uses these valves. The drawing shows them plain but I wondered about wear
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Post by Phil Sutton on May 9, 2005 19:41:27 GMT
Well,I think,for one,that you should have some sort of packing between bore and spool,else you'll have steam blowing straight past,and going to waste.
Either of the forms you mention will do,it will all depend on your skill in machining and/or your own preferences.
Phil
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Post by johnharkness on Jun 5, 2005 20:20:18 GMT
Thankyou for your comments, John.
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Post by Shawki Shlemon on Aug 24, 2006 10:32:20 GMT
Hi Ivan I built a GWR king ,see my live steam models .I also built two other engines with piston valves. 20 years ago or so an English gentleman wrote an article in ME about using PTFE for piston valves .I used PTFE for all the three engines and the results were great.This material has high coefficient of expansion, therefore one need to have more clearance. I worked it out with trial and error to be approximately 0.008" per 1" diameter .The engine will be sluggish running on air or when cold but once is warm it is great .This material is a lubricant as well .  Regards Shawki |
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Post by Shawki Shlemon on Aug 25, 2006 8:53:47 GMT
Hi
It is me again just to let you know where the srticle is,it is on page 664 in Model Engineer 4 December 1987 .
Regards
Shawki
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