Swivel barrel unions, which is best poly, brass or other?

[urbanfarm]

Looking at a build that requires 2-3 swivel barrel unions between 1/2 to 3/4 threads operating at pressures 200psi max and I have a choice of deciding pvc, poly, brass, or stainless for this area of the device which is 18bar 260psi rated PVC barrel/chamber and the yet to be decided other area.

Brass and metal requires effort, tools and sealing compound, and in my current noob experience with brass seem less user friendly, perhaps the stainless is better yes no? although ultimately metal will handle pressure and cold CO2 better and I will use other metal parts where I can.

Whereas PVC and Poly once Joined/threaded seem fairly easy after my H20 plumbing days, however I have never gas pressure tested them before, do they hold up as good or better than the metal unions?

Also next if a CO2 cartridge is used would that then rule out use of PVC? yes/no?

The poly seems appealing at this stage though because it looks more compact than PVC!

[inonickname]

I wouldn't really reccomend poly (I think it's only for water/flow perhaps?). ABS and pvc should work fine, I haven't really had much experience with metals holding that much pressure. Waiting for an experienced pneumatic guy to post would be a good idea.

PVC becomes brittle at lower temperatures so maybe try abs which has a lower/higher temperature tolerance.

[Eddbot]

Yes, unless you have a regulator, PVC is out of the question.

If you are going with co2 find a reg ex. or make the chamber and union some kind of metal, but metal for the barrel isn't as important as the chamber.