View Full Version : small needle valve const.?

scott m
08-10-2004, 12:01 AM
Hello, I am new to your forum. I have a SB w/qc, power-hacksaw and a lot of imagination (among other things...). It appears there are a lot of skilled/talented people on your board and many things to be learned here. I look forward to helping when I can and learning things. Speaking of learning things... and I hope my question is not OT http://bbs.homeshopmachinist.net//wink.gif, but is it possible to make a small adjustable needle valve (brass) to be soldered in line to 3/16 copper tubing? Purpose being to control butane gas flow to a stirling engine burner. Can the seat be cut to match the needle without using built up construction (one piece valve)? Thanks for any replies. Scott.

Forrest Addy
08-10-2004, 12:09 AM
You don't machine a seat angle on a low pressure needle valve. You make the seat a sharp corner and use the needle to swage the sharp corner into a seat config so the seat width is about 1/64" wide or less. Make the needle about 30 degrees included angle out of something harder than the seat/body material and stone/polish the needle cone into geometrical prefection.

08-10-2004, 01:18 AM
"polish the needle cone into geometrical prefection...."

Would that be at the atomic scale Forrest? http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by Evan (edited 08-10-2004).]

scott m
08-10-2004, 01:20 AM
Jeeze, Forrest that was quick. Appreciate it very much, indeed. I like your column, I follow along and learn what I can. Instead of running the needle in and forming the seat, could a very small "o" ring be used with the pressure that a standard butane refill canister would provide? I don't intend to use this method but wonder just the same. Problem solved! Scott.

08-10-2004, 01:49 AM
Sounds like Evan's trying cooking up some new ideas on how to get his polishing even better, if that's possible... All of the project pics I've seen are super shiny, although I guess that isn't necessarily _geometric_ perfection. http://bbs.homeshopmachinist.net//smile.gif

[This message has been edited by Ryobiguy (edited 08-10-2004).]

Allan Waterfall
08-10-2004, 04:37 AM
Have a look at needle valves and spraybars for model I.C.engines. Anything by "OS" will be well made,but all manufacturers make them as spares.


08-10-2004, 08:25 AM
When I made the carburetor for Edgar T. Westbury's "Kiwi" engine, I used a piece of a large sewing needle for the "needle" part of the valve. The needle got Loctited into the shank of the valve. It seats in a drilled hole of appropriate diameter.

I hasten to point out that I haven't actually RUN this engine yet...but the needle valve construction is pertty much per ETW's directions.

scott m
08-10-2004, 10:57 AM
Thanks for all the ideas, I am going to try building this valve myself and see how well it works. I will try to post a picture of it if I can figure out how on this forum. Fire up that Kiwi, SGW! Curious: what type of engine is this? Scott.

08-10-2004, 11:27 AM

I've been tempted to try electropolishing which really does polish at the atomic scale. It needs lots of current and hot electrolyte baths which has deterred me so far. The current aspect is not a problem as my DC welder will work fine as a source but hot acid baths are another story.

08-10-2004, 12:10 PM
"Kiwi" is a single-cylinder engine, 1" bore x 1 1/8" stroke, that was designed by Edgar T. Westbury in the 1930s and published in Model Engineer magazine. He updated the design (slightly) in the early '60s. Castings are vailable from Woking Precision Models (in England) for either an air- or water-cooled version. Think "early British motorcycle engine" for the air-cooled version and you'll have the general idea. I was making great progress on it while I was laid off, but now that I've got a real job again the shop time is pretty sparse.