I'm looking for a source for spring loaded check valves with a cracking pressure less than 5" WC (0.18 psi) for nitrogen service. 316SS/PTFE construction will suffice. Temperature is 0 - 40C. Sizes could range from 1/4" tubing to NPS 2 Cl 150 flanged.So far the lowest CP I've found is 1/3 psi. Below link to a datasheet from a well renowned disc check producer, Flowserve, Gestra (with variation on other product and material qualities from the same producer), could be a possible match to your question and anyway one of the best possible on the market.Competitors/other suppliers exist.Rubber "duck-bill" and diaphragm check valves have very low cracking pressure. Spring loaded valves generally do not have very low cracking pressure because they also have to seal reliably when upside-down or dirty. I've used free-floating ball checks mounted so the weight of the plastic ball sealed the valve.It was a 2" check-valve in a 1/2" line.

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