Mk11 Split-off from Regulator Geeks, Part II

[Bigbella]

If I am making a big of a change such as swapping entire regulator systems, I need not worry about a DIY boot...I will just switch to environmentally sealed SM regs like MK19 or similar from Deep Six.

I am going to see what I can come up with...maybe use the silicone SPEC boot prototypes and figure out some sort of durable synthetic mesh....just a filter or sorts for the ports

I wasn’t suggesting switching brands; but rather, just offering an example of what already has been done, rather than wholly reinventing the wheel. A friend made something similar to the Poseidon anti-freeze cap — a hollow “environmental” boot (affixed with cable ties), from silicone RTV, and a simple mold, for an old Sherwood, if I recall correctly . . .

 

[scrane]

Is there any real issue with Nitrox (<40%) and the SP MK11Ts?

Atomic says they uses Monel for Nitrox compatibility on their Ti regs, but I can't find any SP info on the MK11Ts (or much of any info that they exist at all for that matter.)

Since the Mk11 doesn't hav a piston, we don't have to worry about that part.
Comparing parts schematics between the Mk11 and Mk11T it looks like all parts in the HP side share the same part number outside of the main body which is presumably Ti in the Mk11t and brass in the Mk11.
I would think if there was any danger of a Ti part spontaneously igniting because of a pressure surge it would probably be the knife edge in a piston reg and maybe the HP valve or orifice in a diaphragm. Something flimsy, able to generate but not dissipate a localized hot spot.

Has anyone seen any reports of actual titanium regulator fires? I'm not saying it can't happen, I just haven't seen any detailed reports.

I read an interesting article about a titanium fire in a different context due to the inherent difficulty in milling Ti and creating micro irregularities on the surface.

 

[Pearlman]

Is it correct that the risk of fires is only during sudden pressurisation if the tank is not opened gradually? Everything else I read says the air chills as it flows down the tube.

 

[lowwall]

Is it correct that the risk of fires is only during sudden pressurisation if the tank is not opened gradually? Everything else I read says the air chills as it flows down the tube.

When you first open the valve, there's a large increase in temperature inside the high pressure (HP) section of the first stage as it equalizes with tank pressure. The gas will only chill when you start breathing (or purging) from the second stage. Opening the valve slowly will limit the rate of heating of the gas inside the HP section of the first stage, but the peak temperature will not be much lower. A couple of seconds of valve opening time just isn't long enough for the heat to be transferred from the gas to the metal parts of the reg.

Opening the valve slowly will help limit the size (and perhaps the velocity?) of particles in the tank hitting the filter on the first stage. These can cause sparks that can ignite a fire if there are flammable materials or contaminants in the path.

Note that you don't actually need a spark to have a fire. Some materials will light themselves at a given combination of high pressure and high oxygen availability. This is how diesel engines work.

Here's an old video that's still on point:


edit: crossposted with rsingler. Great minds... If you want to see the full 30 minute video that this was extracted from in all its '90s PSA glory, here you go:

 

[Pearlman]

Interesting thanks. Now coming to the adiabatic compression part - In theory - will pressing the purge button of the 2nd stage while slowly opening the tank valve mitigate the risk? Of course we don’t want to rely solely on operator to prevent fires as that day will come sooner or later when there is an “operator error”…

 

[Geo7]

Since the Mk11 doesn't hav a piston, we don't have to worry about that part.
Comparing parts schematics between the Mk11 and Mk11T it looks like all parts in the HP side share the same part number outside of the main body which is presumably Ti in the Mk11t and brass in the Mk11.
I would think if there was any danger of a Ti part spontaneously igniting because of a pressure surge it would probably be the knife edge in a piston reg and maybe the HP valve or orifice in a diaphragm. Something flimsy, able to generate but not dissipate a localized hot spot.

Has anyone seen any reports of actual titanium regulator fires? I'm not saying it can't happen, I just haven't seen any detailed reports.

I read an interesting article about a titanium fire in a different context due to the inherent difficulty in milling Ti and creating micro irregularities on the surface.

I seem to remember reports on here in the mid 1990s of titanium regs burning, when both Ti and Nitrox were still new. Since then there was the occasional 100% O2 reg that had trouble. I would not worry about it in the 30% range, but keep the reg clean. Over 40% in titanium regs is probably a bad idea...

 

[Geo7]

Is it correct that the risk of fires is only during sudden pressurisation if the tank is not opened gradually? Everything else I read says the air chills as it flows down the tube.

That's my understanding as well. Assuming of course that the reg has no hydrocarbon fuel sources that can spontaneously ignite. There is an article by FLOTEC, a company making aluminum regs for pure oxygen, basically explaining the point you made:

WHY HIGH STRENGTH, ANODIZED, ALUMINUM ALLOY IS SUITABLE FOR USE IN OXYGEN REGULATORS

 

[lowwall]

Interesting thanks. Now coming to the adiabatic compression part - In theory - will pressing the purge button of the 2nd stage while slowly opening the tank valve mitigate the risk? Of course we don’t want to rely solely on operator to prevent fires as that day will come sooner or later when there is an “operator error”…

In theory? Yes.

In practice? Seems like a waste of gas. If you are using 02 above 40%, I'd suggest cracking the valve very slowly and following any other procedures you were taught in your technical training.

 

[rhwestfall]

Great fun if/when you are feathering a valve for a rich mix deco due to a failure.....

 

[Open Ocean Diver]

Any need for special cleaning with titanium regs when using 32 or 36%