Idea for easily fabricated needle valve: teflon core body

[Refluxed]

Trying to figure out an easy way to make a needle valve, and looking at what others have done before, someone suggested filling a tee with solder and then machining out the valve body from that. I figure why not just squeeze some teflon rod inside a tee, which is much easier to machine again, similar to working with wood, and then cover with reducing nipples. Teflon will also expand more than metal when heated, and being constrained by the tee, means that it will form tighter seals.

Anyway, here's the basic idea in picture form:

*different metal colours for visual separation only

A SS threaded insert for wood could be placed in the top of the rod, to take the main mechanical stresses when turning the screw. Also, an interesting part I found, is something called a "swage stud terminal threaded insert". They are made in 316 for fastening balustrade wire rope. I'm thinking they could serve as the needle in a teflon core valve.

The head pressure in a Boka still is next to nothing, measure in centimetres, we don't need several hundred dollars worth of ANSI 2500 (6000 psi) valves to hold back a fraction of a bar. I got quoted $350 yesterday for a 1/4"...

The biggest issue is having teflon rod the same diameter as the ID of the tee. Without a lathe, it would be hard to make a good fit. However, undersized rod could be wrapped in teflon tape, cut in half, and inserted from each end. That leaves just 3 holes to drill (or two, if a seat for the screw end isn't needed), and form-tapping the teflon with a fine pitched screw.

[marshrunner757]

Have you checked ebay? Less than 40 bucks

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[dukethebeagle120]

i got a brass needle valve at the car parts store
works great on my column

[Refluxed]

Yeah, I did, and all the cheap ones came from China, which means a wait, and possible customs delay.

But I did another search just now, and found a couple locally:
1/2" NPT 316 $46
3/4" BSP 316 $40.40

No idea why I didn't see them before.

As for brass, unfortunately, finding salespeople who can tell you technical data (such as: "does it contain lead?") is quite difficult.

[der wo]

I like the idea.
We had similar ideas here:
http://homedistiller.org/forum/viewtopi ... 17&t=26274
http://homedistiller.org/forum/viewtopi ... 17&t=18270
http://homedistiller.org/forum/viewtopi ... 50&t=41474

When designing a needle valve, the most important variable is the diameter of the bore. If you want to use the still only for neutral alcohol, I would build a valve with only 1mm bore, even if it is a 4" with 10kW. When you want to run it like a potstill too, you need a greater diameter. For a 2" 3mm will be enough, but more will run better probably.

[Refluxed]

Yeah, I had read each of those threads regarding DIY needle valves, the idea for a teflon core came after reading the air fitting/bicycle spoke one (actually, I think a different posting on it).

With regards to bore, which bore do you mean? Do you mean the inlet hole to the needle well drilled in the side of the teflon rod? If so, that can be made very small (I have a set of sub-millimetre carbide drills), and a line of them made up the side of the teflon rod, giving relatively linear flow control between stops. Could also increase the number of holes radially for each axial step for nonlinear control. Alternatively, if stops are undesired, a slit could be used.

Also, the reducing nipples aren't needed at all, they are just cosmetic to represent whatever fittings might be there.

[der wo]

Especially the bicycle spoke version is good for a still for neutrals, because the bore is small. Bore is the diameter of the two holes in the teflon rod, the diameter of the valve when it is full open. Yes, when you diy, you can choose the diameter. I think a 1/4" needle valve has around 2mm bore normally, a 3/8" one has 4mm. But I am not sure, I live in the metric world. A 1/4" is enough for a vodka machine any size but not for an all purpose still 2" or taller.
Generally at first you should clear up, what do you want from the still. Only neutral or anything. But considering that in the end it is a very cheap solution, if you get work it, you could build a second valve. Then you have one for neutral runs and one for aroma runs.

A slit sounds good.

I think you will need the nipples for sealing it. Or perhaps you find another solution.

[Yummyrum]

You can always fit a bypass valve across (or in Parallel) with a needle valve if you want unobstructed flow for stripping .....best of both worlds if that's what you want .

LOL thanks der wo for digging up that thread from YHB , Brian was one of my inspirational builders .

[der wo]

Yes. He had a few brilliant ideas. Some more:
http://homedistiller.org/forum/viewtopi ... 17&t=32201
http://homedistiller.org/forum/viewtopi ... 17&t=40063

[Refluxed]

I think you will need the nipples for sealing it. Or perhaps you find another solution.

I was going to heat the tee in the oven, and put the teflon in the freezer, and then quickly press fit them with the hydraulic press, and cool. The rod is supposed to be pressed hard enough against the inner wall of the tee (at least at the ends of the rods), that it won't leak under the mild pressure it is exposed to.

However, without any end caps, over time the rod might start to narrow and elongate due to cold flow. But it shouldn't be enough to compromise the original seal with the pressures it is expected to deal with. In practice, the tee would likely have fittings on at least two ports - the inlet and outlet, to connect to the system.

With my lathe, I can also remove a portion of the thread from the screw, and turn down the end to a needle point