Scubapro O-ring Sizes

[jacked_72]

I went through the rest of the -010 gum orings I got from oringsusa. They're bad. Two cracked when bent (like dried spaghetti). Two are very hard and the third was more bendable. So, it looks like they are still having an issue whith their supplier on these.

 

[Zung]

OOPS! How old are they?

Edit

Sad but true: I just checked my stash, and the older ones have turned yellowish and become hard and brittle.

In the pic, the left one is a sample couv sent me a while ago; it breaks when I try to squeeze it. The right one is from a batch I ordered last month, [-]also from O-rings USA[/-]: it's white and supple as it should be.

Edit Edit

Sorry, Alzheimer hit me again: the one on the right is NOT from O-rings USA; I got it from Mc Master: the label says: "90 Cast Urethane".

 

[halocline]

Is there any good reason why I couldn't just use viton orings on the piston and for the recessed oring in the groove? I notice that the newer scubapro kits no longer use the clear/amber orings in those positions.

Sure, you can use viton. Supposedly it does not have as good abrasion resistance as polyurethane, but I'm not sure how important or even true that is in the context of regulator use. Couv knows a lot about o-rings, and I think he uses viton for that. Usually O2 clean regs use viton throughout.

 

[jacked_72]

They must have sent me some old stuff -they just came in to me this week! Mine are all various shades of yellow/amber. I wonder how long that stock has been around. I've emailed them and asked them to send me some fresh ones. I wonder if the viton o-rings are subject to going brittle like these millable gum rings. I suppose it could have just been a bad batch from the manufacturer or exposure to UV or heat. Whatever the problem is, they're not usable. I'm kind of concerned about using them at all (even if I got fresh examples) since they seem to be prone to going brittle and cracking. Will the viton o-rings do this too? The old nitrile o-rings seem to still be very supple.

On these MK5s, can you hear the piston sort of "pop" into the seat when you turn on the tank valve? I can on mine. Just wondering if that is unusual.

edit: I've added a picture of my orings. You can see the color differential and the way the ones that didn't break stayed deformed.

 

[Zung]

Sorry, I got it wrong: the "good" one (on the right) is from Mc Master.

couv said PU has 5 years shelf life, vs unlimited for Viton & EPDM.

OTOH, there're at least 2 resident gurus here who use those O-rings USA PU stuff and they appear to be still alive. awap, halocline, are you well?

 

[jacked_72]

I just exchanged emails with theoringstore.com about 90 duro viton orings. They're adding them to the website this weekend! Best part is that shipping is a flat $3. I'm going to give the viton orings a shot.

 

[redacted]

Sorry, I got it wrong: the "good" one (on the right) is from Mc Master.

couv said PU has 5 years shelf life, vs unlimited for Viton & EPDM.

OTOH, there're at least 2 resident gurus here who use those O-rings USA PU stuff and they appear to be still alive. awap, halocline, are you well?

I have not checked yet today.

Parker Seals rates the age resistance of millable urethane as 3 to 5 years but cast urethane is in the same 5 to 10 year group as EPDM (Viton is up to 20 years). I had bought a large batch of the PU010-90 and was probably the source for many of the bad ones reported here. I went through mine and found most were that yellowed color and brittle. But some were still that whiter color and flexible. I coated the good one with Tribolube and will see if that helps them in storage. I still favor them because they are supposed to have somewhat better dynamic properties than all other alternatives. I was having problems with IP swing in some Mk10s (10 psi in some cases) as a function of tank pressure. No nibbling on the HP o-ring but I decided it could be caused by extrusion increasing the surface area in contact with the piston stem producing more friction. In any event, the urethane o-rings seemed to reduce the problem so I have been using them in 5 or 6 Mk5/7/10s for about 3 years now. I believe I had one in that time that I replaced due to a slight leak that developed. I doubt if I will buy more of the urethane but I'll continue to use what I have until they become a problem in service or storage.

In any event, if you are buying, I'd suggest you stick with EPDM or Viton unless you run into a problem that might be solved with urethane.

 

[Zung]

I just exchanged emails with theoringstore.com about 90 duro viton orings. They're adding them to the website this weekend! Best part is that shipping is a flat $3. I'm going to give the viton orings a shot.

I bought most of my EPDM 70's from these guys. They are a little bit pricey for lager quantities, like 50-100 pcs, but very efficient for small orders.

Just checked: postage was $5 to Switzerland. Rejoyce!

 

[Zung]

A minor incident: while doing a MK20, I misplaced the 2 original piston crown o-rings, -022 Duro 80, so I used 2 -022 EPDM Duro 70 from The O-ring Store. I plugged the piston into the swivel/cap, but the piston stem wasn't straight. Upon closer examination, there was a small "loop" of the "wiper" o-ring sticking out, no doubt disloged when first pushed in because the material is softer. I removed the piston, wiggled the o-rings a bit, pushed it back in, and it was OK.

For those who fit the piston to the body first, and then the cap/swivel, the risk could be more serious, because it would be harder to see the problem.

Maybe I should use some Duro 90 Viton next time.

 

[redacted]

A minor incident: while doing a MK20, I misplaced the 2 original piston crown o-rings, -022 Duro 80, so I used 2 -022 EPDM Duro 70 from The O-ring Store. I plugged the piston into the swivel/cap, but the piston stem wasn't straight. Upon closer examination, there was a small "loop" of the "wiper" o-ring sticking out, no doubt disloged when first pushed in because the material is softer. I removed the piston, wiggled the o-rings a bit, pushed it back in, and it was OK.

For those who fit the piston to the body first, and then the cap/swivel, the risk could be more serious, because it would be harder to see the problem.

Maybe I should use some Duro 90 Viton next time.

I have never had any problem with the EPDM duro 70 or the Viton duro 75 on any of my pistons. I also extend my o-ring supply a bit on my Mk20s by only going new on the inner (pressure) o-ring and I move to old inner o-ring to the wiper position.