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Needle valve on the cheap? Answered

I need a needle valve or similar to adjust some pressure with more or less precision.
Problems I am facing with commercial solutions at the moment:
Needs to withstand about 300psi max pressure, must survive contionous exposure to concentrated ammonia vapour.
I already wasted too much money on stainless steel valves claiming to be chemical proof and capable of 6000psi only to find out they use seals that turn to goo in the ammonia vapour and fail.
And since the stuff is not really healthy, not easy to get, I would prefer something safer.
Real problem is also that the thing should be able to allow for good flow rates when opened fully.

Modes of operation:
During the active cycle ammonia vapour needs to pass through an opening as big as possible while after that the flow must be shut off.
The reverse cycle needs to be adjustable from closed to fully open with great detail to control the flow rate.

Current ways to compensate:
With a ball valves and extra piping I could seperate the two cycles so I won't have to bother with tiny openings but I would prefer to use only a single connection.
With a bypass around the needle valve this could be accomplished better but still looks ugly.

Materials out of the question:
Copper, brass, normal seals based on rubber, nitrile or similar.

Questions:
I know fully sealed in.line valves exist for LPG system and similar.
Are any of these magnetic valves available for the use with ammonia?
And if so: Can they be operated with a neodymium magnet instead of the coil?

Even stainless steel valves rated for chemical use and high pressure fail quickly on the seals.
Is there anything available that does not use soft seals but for example aluminium instead?

Thinking spray pump here...
One way ball valve systems like used in simple spray pumps are a great thing.
With some aluminium tubing I was able to make a simple valve that with some more attention to detail might even work.
But of course there no other way of moving the ball then to use a magnet and with sufficient back pressure even neodymium ones fail to get the ball in the open position and keep it there.
Now getting this combine with a needle...
If, instead of the ball, a magnet in a teflon shell is used on a spindle I could spin a magnet around the outside to turn the valve with great precision.
Has anyone already designed such a thing or would I have to start from scratch here?

Discussions

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steveastrouk

2 years ago

Get the right seals ! The best stuff is Kalrez

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steveastroukDownunder35m

Answer 2 years ago

Silicone is down as highly compatible against gaseous Ammonia, hot or cold.

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steveastroukDownunder35m

Answer 2 years ago

Its not inconceivable one of the Viton fluoro-carbon rubbers might also be ammonia proof, but Kalrez is phenomenal for resistance.

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Josehf Murchison

2 years ago

Something like this everything made out of nonmagnetic stainless steel but the stepper motor armature magnet. The stator is on the outside and the valve seat can be formed like the valve seat in a cars engine metal on metal.

Chemical Safe Valve.png
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RampedUpDIY

2 years ago

I'm just curious... what are you using the ammonia vapor for? This sounds like a very interesting project.

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Josehf Murchison

2 years ago

What about all food grade stainless steel, the right grade it is nonmagnetic.

The valve can be seated the same as the valves in your car with a feed screw and an induction motor armature sealed inside the stainless. Then you put the stator on the outside of the stainless steel. The magnetic fields from the stator pass through the stainless steel turning the armature and opening or closing the valve.

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Downunder35mJosehf Murchison

Answer 2 years ago

Problem is "inside"...
I have not found much that will survive the ammonia.
Standard plastics won't do it and if there is any part made from copper or brass inside it is doomed to fail.
Plus I have problems getting any decent valve at a reasonable price here.
But the idea itself is nice, will have to keep it in the back of my head!

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Josehf MurchisonDownunder35m

Answer 2 years ago

Just nonmagnetic stainless inside stator windings outside.

The valve I mentioned you would have to make and after thinking about it a stepper motor model would give a more precise response. Ill send a pic tomorrow.

The only other thing is industrial refer parts, large industrial refrigeration still uses ammonia today. But I think you can only get open closed valves.

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Jack A Lopez

2 years ago

Well, I think the most simple kind of valve I have ever seen is a pinch valve. That is a piece of tubing that is elastic enough to pinched closed, plus an external clamp to squash it closed. You know, like a garden hose, with a couple of blocks of wood and a C-clamp.

Of course a typical piece of elastic tubing is going to explode if it has 300 psi inside it, and only 15 psi or so, one atmosphere, outside it.

Although maybe if you used a different shape, and wrapped some steel around the outside of it, it might be possible to build something that would NOT explode with 300 psi inside it.

I mean if you have the ability to 3D-print things out of different kinds of plastics, you might be able to make something that is mostly a big sturdy block, but with some small channels inside, and maybe a cone-shaped plug and a cone-shaped hole that could be brought together just by squishing the whole thing from the outside.

Also I am naively hoping that some of the choices you have for plastic filament (nylon? ABS? HDPE?) will be chemically compatable with your ammonia, or ammonia+water, or whatever it is.

Pages like this,
https://www.coleparmer.com/Chemical-Resistance

give letter grades, A,B,C,D, to different kinds of metals and plastics, for use with different chemicals, but I can't help but wonder how those ratings will hold up in a real apparatus.

Some annecdotal evidence would be nice, from people that have actually seen this stuff, like Steveastrouk telling us about valves with Kalrez(r) seals.

Which makes me think: If you can actually find a valve that will work, at a reasonable price, that will probably be preferable, and a lot less work than building one from scratch.

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Downunder35mJack A Lopez

Answer 2 years ago

I know the valves you mean, used them before to refill antique fridges to get them working again, only difference is they had a port instead of a handle.
Problem from my small scale tests so far (mainly boiling seals in ammonia) the problem is that at elevated temps most seals swell up badly or simply corrode.
I even tried a 1/4" stainless steel needle valve that claimed to be chemical resistant at tested to 6000PSI - the seals failed after only a few hours of operation.
Kalrez I can not find anywhere down here, the suppliers I called did not even know it LOL
Due to the dangers when leaking I am starting to think the only real option to stay safe it use a two way system instead.
Just leaves the question how to create a fully sealed pump style valve that can open with around 150PSI back pressure...
If all fails I just have to abandone the idea of activating the cycle when needed - better safe then sorry when it comes to ammonia....