lube orings oxy

Silicone grease maybe ?

I've been building some high pressure stuff of late (3000-4500 PSI) and except for silicone o-rings which might swell just about everybody says 100% pure silicone grease, and it doesn't take very much at all.

Interestingly there are a lot of good greases for this. Diver's silicone grease, dielectric silicon grease, and even faucet valve grease. They also say absolutely nothing petroleum based as petroleum oils and greases can detonate (diesel) in some high pressure applications.

At handpiece pressures up to say 80 psi, Krytox or Fomblin grease is preferred, but not essential - some silicones will work OK. You can also use some silicone O-rings, though Viton is better.

For oxygen at 3,000 psi, for grease you will _need_ to use a perfluorinated perether like Krytox or Fomblin, which will not burn at all.

Chemical formula of a perfluorinated perether is (CF2O)n, structure is

-CF2-O-CF2-O- . If you heat it in oxygen it forms CF2=O but doesn't react with the oxygen, and doesn't give off heat. Expensive, but you don't need much.

It is not safe to use silicones in high pressure oxygen systems, either for grease or for O-rings. A typical formula for a silicone might be (C2H6Si0)n, and all those carbon and hydrogen atoms would burn brightly in oxygen to form H2O, CO2 and SiO2. And give off a lot of heat.

In pure oxygen at 3,000 psi using silicone grease would be highly bloody dangerous, and could well prove fatal.

It is best to avoid the use of non-metallic O-rings in high pressure oxygen service. If you really need to I can advise, but I do not recommend it.

For compressed air a well-chosen silicone grease is much less dangerous, and like diver's grease may even be acceptable.

-- Peter Fairbrother