fittingplumbing
I'm running a hydrogen gas system that's below 15 psi. All of my fittings are Push-to-Connect fittings of either 3/16", 1/4", or 5/16" OD from SMC. What sort of tubing can I use with this?
Would everyday hardware store vinyl tubing work fine? Nylon tubing? ATP Vinyl-Flex PVC? I can't find any literature about this on the SMC website.
Part of the confusion is 'compression' is sometimes applied to fitting types that are not truly compression type. The term should only be applied to fittings where the compressive force is is applied by screw threads via part of the fitting itself as opposed to compressive force being applied by external tools.
In this compression fitting, via the threads seen on the right of the left hand piece and inside the right hand piece, the tapered ring on the copper tube is compressed, squeezing the tube tightly such that leakage is not possible. Plastic tube variants have an additional insert piece that fits in the end of the tube so it does not collapse under the compressive force.
This is an example of a crimp fitting. The ring is slipped loosely over the tube before pushing the tube onto the barbed fitting.
An external tool is used to apply the compressive force to the crimp ring. The material properties of the crimp ring are plastic, so that when the tool is removed, the ring continues to apply significant compressive force on the tube. Note that this tool is carried in the field to facilitate on-site assembly of piping systems.
A swage fitting is yet another type. It is similar to a crimp fitting in that an external tool is used to apply pressure and a sleeve maintains the pressure after the tools is removed.
The major difference is the compressive tool applies much much more force to the sleeve than a crimp tool. A swage tool is typically not very portable and not used in the field. Rather, pipes are pre-fabricated in a shop with a heavy duty hydraulic machine. The types of fittings swaged to pipes typically allow field assembly using common mechanic's tools.
PEX labeled fittings are uniform (essentially). You can use any pex labeled fitting with any pex labeled tubing and any pex labeled crimp ring, provided they are all labeled for the same size tubing and the manufacturers literature shows as astm compliant. For ordinary residential remodeling you don't need to be concerned with pressure ratings of the assembly.
Note that PEX labeled components are for use with potable water only, unless otherwise noted in the manufacturers literature (I don't know of any exceptions but they may be out there).
Best Answer
You need to use tubing that is rated for hydrogen gas. McMaster-Carr may have some. Likely you'll have to use stainless steel or an exotic plastic like teflon. Normal hardware-store tubing will react, possibly violently, when used with such fluids/gasses in them. If you're cracking water into hydrogen / oxygen, that line will need to also be customized for carrying mostly pure oxygen.