Question Sherwood 5000 K-valve /Luxfer Al 80 tank seal

[toddster541]

Hi all,
I'm out cruising in the Sea of Cortez on my sailboat. No access to a dive shop anytime soon.

This morning I was filling my tanks and one started audibly leaking around the valve base at 3000 psi. I've been a little suspicious of that tank for a while because a few times, it seemed to be only partially filled when I started a dive, though I was pretty sure I filled it as usual.

Luxfer 80 cf aluminum, ca 1991 with Sherwood 5000 K-valve.

Anyhow, suspecting an o-ring issue, I emptied it and unscrewed the valve, only to find... not an o-ring but a flat-faced seal, a little wider at the top than at the bottom. Fully fills the groove on the tank. Looks like the top edge has been extruded a bit. Can't find anything like it on line. I replaced it with a -214 o-ring, which seems to be holding ok at 3000 psi. But it's not what was in there. (O-ring fits on the valve stem just right, but doesn't fill the groove on the tank.

Dunno - I've always had these tanks serviced at shops, never took them apart myself before. Anybody know what I'm talking about and source for these seals? I'd like to add some to my resupply cache.

Lost an afternoon dive over this issue.

Maybe the o-ring will hold up temporarily forever...

 

[Scared Silly]

Yeah, that is what they look like after a long time. I just replaced one that looked similar on a cylinder I have not used in a long time. Happens when the o-ring is not replaced regularly.

 

[toddster541]

Thanks, I wondered if that might be the case. But it seems as if the 214 O-ring would have to expand to take this shape. Not sure how that happens under compression.

Man, there are big sea turtles all around the boat. I suppose they'd just dart away if I tried to quickly splash in before dinner.

 

[rjack321]

Thanks, I wondered if that might be the case. But it seems as if the 214 O-ring would have to expand to take this shape. Not sure how that happens under compression.

Man, there are big sea turtles all around the boat. I suppose they'd just dart away if I tried to quickly splash in before dinner.

They turn basically square as they get old. They are in compression but the force on them in the groove is actually lateral. So imagine the gas is trying to extrude them through the tiny slit between the valve and cylinder. The gas smashes them into the square groove so they never come out round after use

 

[tmassey]

I find that O-rings that have spent more than a couple of years on a tank become completely triangular in cross-section, to match the bevel of the O-ring land in the tank. And looking at them, it seems as if the material has even changed consistency, from rubber to plastic. And I too have thought that the volume of the cross-section seemed larger than what it would’ve been had it been a round O-ring.

The first time I pulled off one of those O-rings, like you I thought for sure they had used some other item besides a typical rubber O-ring to seal that tank. Nope: just a very old, very tired piece of rubber trying to the very last to do its job. Once you open up a few tanks of that vintage and pull similarly-altered O-rings off, you get used to it.

I’m not at all a fan of the current state of scuba tank VIP. I’m not fond of the money grab, I’m not fond of the exaggerated fear dive shops create, etc. But after you open up a few tanks and find completely altered O-rings, or water that has been inside of a tank for who knows how long… You understand why it was created: there’s a great deal of value in popping open a tank every once in a while, looking inside to see if anything has changed, and take the opportunity to clean and lube the valve and install a new O-ring.

Maybe doing that every five years as part of a Hydro is sufficient. But some sort of periodic maintenance is certainly a good idea.

Anyway, now that you have found a problem, it’s time for you to do just that: service the valves, replace the O-rings. Go diving.

 

[happy-diver]

Yeah I open tanks and go oooh look at that clean tank and then seal it up with an oring old or new and then fill it
Just like a shop does
Yeah I open tanks and go oooh, look at that rusty tank and then seal it up with an oring old or new and then fill it
Just like a shop does