Housing o-ring growing?!

[dfx]

I have a Canon housing for my PS 100 that I have used successfully for many dives. On our last dive trip, one day suddenly I couldn't close the housing any more. The o-ring suddenly was too large to fit. Comparing it now with the unused spare o-ring that the housing came with, the old o-ring is not only larger in length, but thicker in diameter and also feels more floppy than the unused o-ring. Is this normal? I know that o-rings wear out over time, but I never expected it to happen in this way. It's almost as if the o-ring absorbed something and grew larger.

 

[Doubler]

If you are not using the recommended Silicone grease what you are seeing is one of the reactions: swelling. Check your grease.

 

[dfx]

If you are not using the recommended Silicone grease what you are seeing is one of the reactions: swelling. Check your grease.

Hmm, I have several tubes of silicon grease here, from different housings... I guess that means there's different types and you can't mix and match? Is there a way to counteract this or is this o-ring toast?

 

[Doubler]

Toast. Cut it in half and trash it. The issue is that the chemical compound in some orings reacts differently with different formulas of greases. Different companies use different formulas for both. This come from over 40 years experience with orings used in underwater environments.

 

[Gilligan]

As stated the wrong type of grease will destroy an O ring. Stretching in size is a prime result. If you don't have Canon grease you can use Sea & Sea grease in the yellow tube with the blue cap.
This website in the UK states what brand O rings are compatible with the Sea & Sea grease:
Sea & Sea O-Ring Grease from Bristol Cameras UK

 

[bvanant]

Once an o-ring has swelled there are a couple of ways to fix the problem but not all of them can work. If you NEED to save the o-ring then soak it in a solvent (hexane or acetone perhaps) that can remove the swelling agent. Then dry it in a vacuum oven at 40C or so. That sometimes works, buying a new o-ring and using the right grease (Tribolube/Christolube/MolyKote) will keep it in shape.
Bill