Out-of-the-box ScubaPro reg for 50% Nitrox?

[AbyssalPlains]

Hi all, I'd like to use a ScubaPro Mk5 out of the box for 50% deco mix. I know they come up to 40% out of the box and I'm not looking for answers the manufacturer or a shop would give me. I want to know if I really (as in, REALLY) need to O2-clean this reg. 40 vs. 50% sounds like it shouldn't matter from a physics point of view.

 

[redacted]

"Out of the box" wouild be silicon lube and nitrile o-rings.

 

[AbyssalPlains]

"Out of the box" wouild be silicon lube and nitrile o-rings.

Um, yes? And what does that mean with regard to 50%?

 

[redacted]

The silicon needs to be removed and replaced with an O2 compatible lube. The nitrile o-rings will suffer accelerated degradation in high O2 so might as well change them out to EPDM/viton.

 

[bamafan]

It's up to you but I would do it with mine.

 

[halocline]

I believe awap's comment was about your 'out of the box' description, implying that you have a MK5 that has the original o-rings and lubricant. If so, I'm impressed......but I wouldn't dive with it. Those o-rings would be 30 years old.

Anyhow, if you rebuild it with viton o-rings and PTFE grease, the only thing left to consider is the seat. I don't know what that seat material is and consequently how it would hold up to high % O2. That said, it's not like a tank valve seat that is constantly exposed; it's only exposed for the duration of the dive. If I were in your position I'd dive it with confidence but inspect it after a few dives to make sure it's not reacting poorly with the high pressure O2-rich gas. I'd be rather surprised if there were any problem.

You could see if SP ever made a MK5/10 seat for higher % O2 use. I don't think so. I believe they have such a seat for the MK20/25, and it also fits the MK10+. (I think) That might be why DA Aquamaster has posted that he uses MK10+ as stage regs.

To me the old 2 port MK5 would be an excellent stage/deco reg if you can get a DIN fitting for it. And there are lots of those around for practically nothing. The only rub is the seat.....who knows if there is any long-term problem using the standard seat. Probably not.

 

[Couv]

.......Anyhow, if you rebuild it with viton o-rings and PTFE grease, the only thing left to consider is the seat. I don't know what that seat material is and consequently how it would hold up to high % O2......To me the old 2 port MK5 would be an excellent stage/deco reg if you can get a DIN fitting for it. And there are lots of those around for practically nothing. The only rub is the seat.....who knows if there is any long-term problem using the standard seat. Probably not.

Teflon has an oxygen index (Oxygen Index ASTM D2863) of > 95% so it should be fine for 50% O2.

 

[halocline]

Wow Couv, good find, the thing is I don't think the newer conical seats are teflon, at least they look and feel a little different than the old shiny flat white ones. Maybe they are, who knows. I guess one could specifically use the old flat seats if you could find them and don't mind the slightly lower flow/higher noise issues.

But I suspect that divers have been using regular HP seats for deco mixes on thousands of occasions without any problem.

 

[NCadiver]

There is a course on O2 servicing and they go into why they do what they do. And you should adhere to what the manufacturer recommends since you did not understand what Awap said. If not make sure you have a video camera with you so we can all see the blue flame underwater like the other guy who knew more than the manufacture.

 

[AbyssalPlains]

I'm sorry, guys, my bad. It's not an Mk5, it's an Mk2. Brandnew. I apologize for the confusion. From a physical point of view, I can't imagine a reg being good for 40% O2 but not 50%. Here is why:

With 40%, the pO2 at 3,000 PSI = 1,200
With 50%, the pO2 at 3,000 PSI = 1,500

If I dive 40% in a high-pressure tank (for which the reg is cleared as far as I understand), the pO2 is 1,400 at 3,500 PSI. That's only a 7% difference of what the pO2 would be in a 3,000 psi tank with 50% mix.

Is my logic flawed?