Rebreather Maintenance

[ghosch]

Questions for the other rebreather divers out there:

How often do you completely break down your unit, lube O-rings, etc?

What else do you do for regular owner maintenance?

[Inspirationdiver]

I check all my o-rings every time I assemble the unit. They don't need to be greased every time, I usually end up adding grease about every 10-20 dives. As far as other maintenance, after a weekend of diving I usually let the unit sit assembled for a day or two before I take the time to do anything to it. Then I rinse out all the hoses and counterlungs, sterilize them, and then lay everything out to dry. It only takes about 10-15 minutes to do everything.

[ghosch]

When you do "tear down" the unit and regrease, do you disassemble the mouthpiece?

[Inspirationdiver]

No, I wouldn't recommend tearing the mouthpiece apart all the time. It's one of those things where if its not broken don't fix it. There is one dynamic o-ring in there that is a high wear part. It's the one you can see in the mouthpiece when you open and close it. You will have to take the mouthpiece apart and grease this one every once in a while, but if it is functioning fine I wouldn't mess with it.

[ghosch]

BTW, thanks for stopping in and filling bottles at the shop!

[john j]

I agree with Inspiration diver that you only should tear apart the mouthpiece assembly if you see problems like a leaky o-ring or one way valve, or if the shutoff valve gets sticky or hard to turn. I have about 150 dives on my unit now and I have only done one mouthpiece service at about 100 dives. The valve was getting a bit sticky so all I had to do was lube o-rings. Didn't have to replace anything. It's not hard to take apart but there are some screws that bite into plastic that I think you probably don't want to be taking apart a lot.

I have never completely torn down my unit meaning taking everything possible apart. I don't think I'll ever do that as a prentative maintenance. I will fix things as they break or wear out and possibly rebuild the first stages every 2 years or if there is a problem. We leak test the system before every dive so if there are o-ring problems, they will show up easily during the test.

There is more maintenance than open circuit equipment, but in my opinion is isn't a huge amount. If you're already a tech diver who owns a few sets of doubles and several regulators, it won't bother you. If you are used to throwing on an 80 and jumping in, then it will seem like a lot of maintenance. If you are diving the Dolphin rebreather now, it's just a bit more maintenance than that perhaps.

[ghosch]

Thanks for the info.

I never had good luck pulling negatives on my Inspiration from the day it came out of the box. This is in contrast to my Dolphin, which always held a negative.

About a week ago I did take the mouthpiece apart and grease the o-rings. It seemed to do the trick, as now my negatives hold for 10-12 hours instead of 10-12 minutes.

Just curious how often I might need to do this. I guess the answer is "when I start having problems pulling a negative again."

[Inspirationdiver]

It can be difficult to tell which o-ring is not sealing and causing you to fail the negative pressure check. Whenever I am having problems, I do the positive check and spray a mild dishsoap solution on all the fittings with a spray bottle. You can easily identify where any leaks are, just look for the formation of bubbles. It really depends on personal tolerance as to how long the negative check should hold. Both the positive and negative checks are important and should be performed before every dive to verify the integrity of the loop, but they are extremes. In the water the loop is at ambient pressure and is less likely to leak. Plus, in most cases a very small leak would allow air to leak out of the loop, not water in. Oh, and you're welcome for the fills. Have fun this weekend.

[jasondbaker]

Guys, what does "pulling a negative" mean?

[ghosch]

There are a number of tests that you put a rebreather through prior to diving it.

One of them is a positive test, where you inflate the system until the relief valve relieves, let the system sit, and ensure that there are no positive pressure leaks. In the case of the Dolphin, you set a 5lb weight on the breathing bag, if it drops you know there is a leak. The positive check on the Inspiration is somewhat less scientific.

A negative test is just the opposite. Using your lungs you evacuate all of the gas from the breathing loop and "scrunch" up the breathing hoses. If there is no leak the hoses will stay kinked. If you come back 5 minutes later and find the hoses are no longer kinked, you know you have a leak to find.

Both tests are designed to ensure the integrity of the loop prior to diving the unit.