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getting there..... now for the slide valves

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michael burton 107/02/2012 03:16:03
126 forum posts
32 photos
hi all when machining the slide valves is it the nut that holds them against the cylinder face? i will be ordering them this week just would like to know before i start the machining as im going to have to change a few measurements due to the previous builders positioning off the steam ports.
thanks to you all once again much obliged
Tel07/02/2012 06:40:49
157 forum posts
28 photos
No, the nut should be free to move in it's slot - the valve should be held to the port face by the pressure difference between the steam and exhaust cavity sides.
JasonB07/02/2012 08:02:02
22755 forum posts
2654 photos
1 articles
AS tel says you want a few thou end play so the nut won't hold the puck off line and a bit more clearance so the puck can lift off the valve face to let any condensate out of the cylinder and prevent hydralic lock.
michael burton 107/02/2012 13:27:35
126 forum posts
32 photos
thanks guys
mgj07/02/2012 18:31:47
1017 forum posts
14 photos
You want the absolute minimum of clearance, while allowing the slide valve to move vertically, as the others have said. Excess clearance = lost motion and less precise timing (as does poor dimensioning). I worked to .001 plus the calculated allowance for steam at operating temp for expansion, because it mustn't jam. The expansion figures are in The Model Engineers Handbook, as are the steam temperatures for given pressure. .
You also want a really good finish on the portface, because that, or the film of oil on it, is the seal between exhaust and live steam, and you don't want live steam headed for exhaust, and not bothering with the cylinders in passing.
Check also that the valve does not lift at all when it is moved by the rod.
michael burton 107/02/2012 23:26:06
126 forum posts
32 photos
hi mikew just building a tich the chassis is getting there jus the valves and nuts to make now oh and the steam tees then should be running on air =)

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