Needle valves for a Boka

[bastardsquad]

I'm building a 2" boka head for a modular still and I'm currently sourcing the needle valve from a commercial supplier. I explained what I wanted to the sales rep, and yes, all good they have stainless in 3/8 and 1/4". The rep knows what I want it for, and he asked their supplier about compatibility with high alcohol% liquids - apparently the needle valves have either a PTFE or a Teflon seat where the needle rests against to form the seal. I know PTFE is about the only plastic this community tolerates - but my question is this: Do all Needle valves have a PTFE/Teflon seat where the needle rests against to form a seal? The rep said metal on metal isn't available, because it doesn't seal ???

[googe]

As far as I know, PTFE is Teflon, you should be able to get a valve that is metal on metal in the gas sector.

[bastardsquad]

Wouldn't metal on metal leak, especially if for gases, which need a tighter seal than liquid?

[googe]

Not if it's engineered properly. Think about valves in a engine head.

[YHB]

The valves you are looking at are probably rated against leaks in a system that operates at 150 pounds per square inch.

In a Bokakob you are talking about a liquid pressure which is negligible.

I make needle valves with a stainless needle in a hole in a brass cap and they do not leak.

If I can do it with a file and a hand drill I am sure that a valve manufacturer can do the same.

[bastardsquad]

The valves you are looking at are probably rated against leaks in a system that operates at 150 pounds per square inch.

In a Bokakob you are talking about a liquid pressure which is negligible.

I make needle valves with a stainless needle in a hole in a brass cap and they do not leak.

If I can do it with a file and a hand drill I am sure that a valve manufacturer can do the same.

This makes sense, as I thought gas would need a better seal than liquid.
That aside, anyone have issues with a needle valve with a PTFE seat for the needle? Chemical compatibility? Longevity?

[YHB]

The resistance properties of Polytetrafluoroethylene AKA PTFE is more than adequate to cope with boiling ethanol and the other constituent in a still.

Longivity, as I said earlier these valves are designed to be in continuous service in high pressure applications, the stress we put them under in a Bokakob on an infrequent basis is not likely to task them at all.

[gatorpit]

home depot, 1/4" 5.75can 3/8 7.35, they are metal; on metal,

[rad14701]

Don't over-think things... It's just a needle valve... You're squandering far too much time on a simple valve whose purpose is to meter unpressurized liquid... It will never need to deal with any pressure at all... Buy a valve and be done with it...