Closed Loop Pressure Relief Valve PSI Question...

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What psi pressure relief valves should I put on my closed loops system? 125? 250? 300? Also, are brass ones acceptable? Thanks in advance guys!

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What are you running for a solvent? I’ve never seen more than 90psi with n butane and a nitro push prior to venting. Propane runs at a higher psi. More info is needed.

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N-Butane.

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It’s a question of what size vessels you use not solvent . Ie 12” triclamp fails at 150 at 100f 6” triclamp fails at 300 (depending on clamp manufacturer) and so on so what triclamp sizes is your system outfitted with?

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for starters I would check out the max psi rating for whatever vessel/column you are putting a prv on and go at least 50 psi or so lower than that .keep in mind to also look up any accessories like sight glasses, clamps,etc. I had some i used from swagelok that were 150 psi

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1.5 and 3"

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Thx Terp.

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The brass prv is acceptable their are stainless ones that are adjustable aswell. What is your collection pot size?

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4 x 30ish lol…

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The PXP I trained on had a 300 psi PRV and I was told the gaskets would probably fail first.

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Also very much dependent on what clamp hardware you are using, single pins are rated for significantly less pressure across all sizes than the double bolt style are. I’d like to think people aren’t using the single pins on closed loop systems but I’ve seen some dumb stuff before…

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you want to use a ptfe/ss check valve underneath your stainless steel prv. this will prevent leaks under vac, as the prv valves are made for positive pressure. you should have a prv on every part of the system you are able to sequester between valves, this prevents hydraulic rupture of the hoses/spools. Select a prv that is half of what the lowest part of the system is rated for. We use a 90 psi relief valve, due to the fact that the largest part of the system is 12".

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Any chance you could link an example of the type of check valve you’re talking about @Soxhlet ? I hadn’t thought about negative pressure messing with the PRVs, but it makes sense. Thanks for the tip!

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I like these, get one with a ptfe ball and a low cracking pressure like 2 psi. Make sure you install it the correct way, otherwise your prv wont work.
https://www.swagelok.com/en/catalog/Valves/Check/High-Purity-Check-Valves

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Is 8psi cracking pressure to high?

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I like 3-5 personally, but 8psi isnt too far off.

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Is the trapped air between the check valve and prv a issue? Am I overthinking(or incorrectly) it or should one press it out the prv with process gas?

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I used swagelok adjustable PRVs on my MkII and MkV terpenators with great results. Swagelok told me the way their PRV’s are built, vacuum isn’t an issue and a check isn’t needed. The seat is sealed from above with the relief spring and valve assembly and any vacuum would just make that seal tighter.
https://www.swagelok.com/en/catalog/Product/Detail?part=SS-RL3M4-F4

I think Parker makes some just like them:
https://ph.parker.com/us/en/6000-psi-relief-valve-r-series

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Thanks for sharing! I hope that to be accurate! I know @Graywolf went out of his way to get them to make a custom assembly outta both the prv and check, swagelok part # SKUPHA-001

Your link brings up another question.

Is there a reason to use the R4 over a RL4 or vice versa? Having the higher range on the R4 seems unnecessary, but has been the common recommendation from others that Ive seen.

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I never went over 75psi for a setpoint.

One could always call and confirm what I was told a few years back by swagelok about vac not being an issue. It took me a week or so to get an answer when I was on the hunt for this in 2012. The two RL3’s that i’ve used have been stellar. I only set one off once on my MkII doing some dumb shit with an Appion way back when. I must have missed GW getting a custom PRV made because I don’t remember any of that, and I was around for all that back then. Heady days.

I can tell you that, in my experience in the natural gas production field, the vast majority of our PRV’s were built very similar to the small swagelok’s and parkers linked above. We ran many different PRV’s under vacuum on our incoming separators and had very few issues with leaking. The gas stream has to be virtually oxygen free(<10ppm O2), so we couldn’t afford a leak under vac, for both safety and economic reasons, but we never used checks.

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