Older Sherwoods and Nitrox

[Aquanaut2000]

I've got two sets of Sherwood regs from the 1990s and have just completed my Nitrox cert... finally.
1- Why do the older Sherwoods have so many Nitrox warnings? Is it because of the "open" 1st stage design with the air bleed and the chance that some gunk can build up inside the 1st stage potentially igniting the Nitrox mix?
2- What exactly is in the Nitrox Conversion Kit (4000-15N) that changes the regulators to being Nitrox ready? Aren't regular o-rings fine until 50% oxygen? The online picture of the kit just looks like a regular 1st stage service.
3- Why does Sherwood say that if they are converted by using 4000-15N kit can the regs only be used exclusively for Nitrox? Is this just being overprecautious due to the potential of me having dirty fills from some old dusty shed without proper air membrane filters?

We dive:
a) Sherwood Blizzard srb 3900 with a srb 3601 1st stage (this service manual has no warning about Nitrox)
b) Sherwood Magnum II srb 3300 with a srb 2100 1st stage (this service manual has tons of Nitrox warnings)

I have a live aboard trip to the Great Barrier Reef coming up in January and was planning on diving Nitrox for the week. I'd really rather use my own Sherwood regs but definitely won't risk any accident.

PS I've read heaps of threads on Nitrox safety (the one where the Sherwood rep was responding) and was hoping someone could clarify some of the details above... thanks

 

[chillyinCanada]

I've been diving nitrox on my Sherwood Maximus from the late 90's with no problem.

Perhaps you are confusing with needing nitrox clean regs?

@rsingler

 

[rsingler]

I've got two sets of Sherwood regs from the 1990s and have just completed my Nitrox cert... finally.
1- Why do the older Sherwoods have so many Nitrox warnings? Is it because of the "open" 1st stage design with the air bleed and the chance that some gunk can build up inside the 1st stage potentially igniting the Nitrox mix?
2- What exactly is in the Nitrox Conversion Kit (4000-15N) that changes the regulators to being Nitrox ready? Aren't regular o-rings fine until 50% oxygen? The online picture of the kit just looks like a regular 1st stage service.
3- Why does Sherwood say that if they are converted by using 4000-15N kit can the regs only be used exclusively for Nitrox? Is this just being overprecautious due to the potential of me having dirty fills from some old dusty shed without proper air membrane filters?

We dive:
a) Sherwood Blizzard srb 3900 with a srb 3601 1st stage (this service manual has no warning about Nitrox)
b) Sherwood Magnum II srb 3300 with a srb 2100 1st stage (this service manual has tons of Nitrox warnings)

I have a live aboard trip to the Great Barrier Reef coming up in January and was planning on diving Nitrox for the week. I'd really rather use my own Sherwood regs but definitely won't risk any accident.

PS I've read heaps of threads on Nitrox safety (the one where the Sherwood rep was responding) and was hoping someone could clarify some of the details above... thanks

This topic has been discussed at great length on many other threads. I'll see if I can't point you to a couple to bolster what I am going to say. I'm a certified Sherwood tech. No. It's not due to Sherwood dry bleed design. No Nitrox risk there.

FIRST, Nitrox has a long and complicated history borne mostly of fear of the unknown. Did you know that PADI actually opposed the use of Nitrox as dangerous tec diver stuff for several years until its obvious benefits and safety became known?
There is an entire industry of tank inspection training (PSI/PCI, and yes, I'm certified by them too) devoted to pointing out the dangers as defined by the CGA (Compressed Gas Association) of any high pressure gas over 22%.

ALL of this revolves around the explosive danger of oxygen due to the combination of adiabatic heating and hydrocarbons in the presence of oxygen.

So. To your question. There is NO danger to your using Nitrox from your tank with your Sherwood regs. NONE. You will be diving up to 40% (and more likely 32% on a trip) and your regs will perform perfectly with Nitrox.

All the warnings and special "kits" are legacy items which date from when mfrs had to be seen to be addressing the "dangers" of this new mix. Manufacturers now universally state that their regs are good for up to 40% Nitrox right out of the box. They don't bother with the green caps and special warnings because there is no hazard.

The kits moved from nitrile to EPDM to Viton orings, because of their decreased flammability. But even nitrile is just fine for any oring except perhaps the high pressure seal for your yoke bolt to the body of the reg, and perhaps the piston shaft seal. But Sherwood has long since gone over to modern materials with all their kits because they also have longer shelf life than nitrile.

In other words, you're good to go.

Are there dangers? Yes. But those revolve around diving with 80-100% oxygen in deco bottles and not keeping your first stages clean. This is where Sherwood's comment about having dedicated Nitrox regs comes from: the orings and other flammable components will only be exposed to "oxygen clean air", or OCA. They won't get contaminated with hydrocarbons.

The risks revolve around filling tanks. They revolve around high pressure connections and pure O2. Not stuff you'll see.

I ALWAYS bring my own gear on trips. It's absolutely frightening what is rented out, especially in high volume establishments. Have fun!

 

[herman]

I completely agree, I use nitrox (32-36) in all my regs, the regs use nitrile orings and silicone grease. The orings might not last quite as long but then again, they are replaced way before they are affected by the higher O2 to the point of causing a problem.

 

[Aquanaut2000]

@rsingler @herman @chillyinCanada Thanks for that excellent breakdown! Really appreciate all your help.