Source of Gas Liquid Check Valve

How much pressure is the gas under?

Could what you are trying to accomplish be done with a trap instead of a check valve?

The system pressure is supposed to be ambient up to about 10 psig. There is a frit filter on the gas outlet tube of the system leading up to a vertical separator (after a copper cooling coil for condensing water vapor since source will be up to 100 °C or even higher, although nominal is about 85 °C. My concern is the pressure drop across the frit filter under flow will tend to hold up condensate return, unless static head can compensate for that loss.

I was just looking at PowerDyne thermodynamic traps. A steam trap could work pretty well I think, since I want water to flow out in one direction, and to block gases and vapor flow in the opposing direction.

Unfortunately, I am already guessing those ones might be out of my imagined price range. Or not.

Almost sounds like one of those heat traps for a hot water heater. Have you considered one of those? How 'good' of a check valve does it need to be?

Good luck with your quest.

Do they have these in your basic hardware store? I could see using one of those if I have a U-tube to hold liquid to float the ball, then when static head is high enough, the ball will drop just enough to pass condensate back to the system.

Probably more like a Home Depot or Lowes or a plumbing supply house. I figure if they sell water heaters, they probably sell these gizmos as well. Hardware stores can be crap shoot. Some of them are HARDWARE stores, others are more like a 'home goods' store.

Did you see this one already?

No. But I saw some like it on US Plastics web site. The crack open pressure does concern me since I will be operating with a limited static head, I think.

Can you locate the check valve at the bottom of vertical run of pipe/tube long enough to build up a bit of liquid head?

Can you put a U-bend in the pipework so the liquid flow is upwards? Then use a standard ball-type non-return valve, eg George Fischer. Available in uPVC or PP. Your size might be a bit small, maybe 3/8" is smallest, but would an oversized valve hurt? I doubt it would cost over $25.

Look up "air relief valve" in irrigation supplies.

What you describe is the reverse of their intended (normal) operation, where gas in a water line accumulates under a ball that drops and lets it out.

Basically, the ball floats on the contained fluid. If mounted upside down, then would only open when there was liquid to float the ball. (Would need "U" fitting with TWL matched to seat height.)

Note this would have difficulty in high liquid flow condition as it would jam the ball shut.

There may be some similar fittings in that range, though temperature limitations may ba an issue.

I'm sure know, but just a comment on use of ball-type NRVs as air release valves (using a ball SG < 1). Only works on initial fill, once the ball is on its seat it only takes a moderate pressure for the upward force to exceed the ball weight, any incoming air is at same pressure as the liquid and the ball stays on its seat. I've had to explain it to a few people who should have known better!

Of course a proper air release valve has a bigger ball, a smaller seat area, and usually a lever to increase the force.

I am replying to Codemaster, although all of you have asked questions:

1. Yes, there will be a an offset level where some water should accumulate in the down leg of the condensate separator. Doubtful I can make this more than about 6-8" water head, since all parts still have to fit inside calorimeter enclosure.
2. Yes, there will be a U-tube on the water return such that a standard check valve (free ball, not spring loaded) should work. If very small amounts of gas leak by I will know, because the tubing is transparent Tygon tubing.
3. To avoid problems with foaming (noted on first trial run with previous separator), the system will be dosed with one Gas-X capsule contents (in about 500 ml liquid)
4. Flow of condensate should be really low, in the 50-150 ml/min range, gas flow in the range of 50-450 ml/min with the higher flow at elevated temperature.
5. The purpose of the calorimetry will be to gauge heat balance between electric power in and heat flow out of the reactor, then the heat content (by burning) will be done on the gases. Flash-back arrestor is in hand, but not installed yet. I Still need to adapt NPT to thread type of normal welding flash arrestor.
6. I may have to collect the gases in some sort of container, and burn them off away from the electrolysis reactor at least at first, as I am finding myself somewhat reluctant to blow everything up. Hydrogen, oxygen, water, and X are in the gases leaving the reactor.

Could you use a simple u trap and let the water provide the reverse gas flow prevention?

I will try that first, and see how it rolls. I suspect it will not work, due to strainer on gas outlet, and open tube on condensate return, thus there could be a pressure differential that would favor reverse flow in the condensate line.