O-rings kit? Which o-rings to carry?

[Peter69_56]

I have never heard of polypropylene O-rings, either they are Buna (nitrile), Viton (FKM), EPDM, or Polyurethane. If they are polyurethane it could be that they are old and lost their elasticity. I believe the shelf-life of polyurethane O-rings is less than 5 years. Of course I am assuming you are using the correct size and durometer for the application.

A few years back, some regulator manufacturers started using PU O-rings because of their superior abrasion resistance. I believe they no longer use them because of the short self-life.

You are correct, I got my poly and my poly mixed up.

They were Polyurethane and they were soft so not old stock and they were the right size, exactly the same as the old O ring, yet would fall out sometimes. On another reg I have the old one still in yet it stays in fine. Maybe the duro is incorrect? I started using Viton and they stay in fine.