O-Rings, Grease and other stuff

[bvanant]

In a recent post there was lots of discussion about what kinds of grease to use on what kinds of o-rings. My take on all this is that in spite of the opacity that manufacturer's use to hide their materials from the users there are only a few combinations of things that we need to think about. Most o-rings are made either from buna-n (nitrile) or silicone rubber (polydimethylsilane). Most buna-n o-rings are black but they can be in other colors. Most silicone rubber o-rings are not black but they might be. O-ring greases come in three main flavors, silicone grease, fluorosilicone grease and non-silicone types like Christolube and Tribolube.

Buna-n o-rings are compatible with all of these types of greases. You can use silicone grease, fluorosilicone grease or one of the Christo/Tribo Lube greases with no problems.

Silicone o-rings on the other hand may swell significantly if you use a silicone grease but they work fine with fluorosilicone greases and the Lubes.

This is kind of like blood groups. Fluorosilicone grease (molykote and S&S blue cap) and the Lubes are universal donors, they can be used on both Buna-n and silicone o-rings. Buna-n is a universal acceptor (except for vaseline type mineral greases) since it can be used with any of the common o-ring greases.

For more compatibility data go to
http://www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf
for some data (lots of data).

Bill

[jcclink]

Some manufacturers insist on using special compounds & greases for no good engineering based reason. Just to distinguish their products from others. Buna works fine for all our u/w photo gear. No need for colored o-rings & "special" greases. The only advantage to using a silicone o-ring for main seal is that it doesn't require grease - no other reason. Silicone is mostly for high temperature applications & is not best suited for water applications compared to buna. I would suggest changing everything to buna & use a good quality silicone grease - same grease for everything. Life would be much easier.

[divengolf]

BTW here is a source for most o-rings. They sell in quantity so don't order 1 or 2 or even a dozen. Still they are much cheaper than buying from the housing manufacturer. For example I checked on o-rings sized for my housing push buttons. Both 100 and 500 were the same price, $10.00 plus shipping.

One order will last a lifetime, or go in with a dive or photo club.

http://www.marcorubber.com/orings.htm

They also have a sizing chart that is quite useful.

O-ring Sizing Chart (http://www.marcorubber.com/sizingchart.htm)

[jcclink]

Just be careful about sizing. Most housing o-rings are metric (JIS) sizes.

[bvanant]

Just be careful about sizing. Most housing o-rings are metric (JIS) sizes.

and for some reason, JIS sizes use the metric system but they are decidedly not metric sizing.
PITA
Bill