Nitrox vs regular service kit - Scubapro Mk2+

[iointerrupt]

I actually made a Kel-F seat for a Mk10 last week. Didn't work though, got mushy unpredictable lockup. Then again my homemade PTFE seat did the same. There seems to be more to these HP seats than just "round slug of plastic of the correct height".

 

[jale]

Hi
Good timing.
I've just replaced my oxy reg on my oxy rb.
Do I use a special Nx reg? No just a brand new MK2 and that's it.

 

[rjack321]

I actually made a Kel-F seat for a Mk10 last week. Didn't work though, got mushy unpredictable lockup. Then again my homemade PTFE seat did the same. There seems to be more to these HP seats than just "round slug of plastic of the correct height".

Yeah. Despite being "better" in a high fO2 environment those are way too soft. The design of scuba regulators is unfortunately such that only the nylon seats have the right behavior. Alas they can scorch in a high fO2 environment, best to keep the rest of the inside scrupulously clean & hydrocarbon free.

 

[rsingler]

only the nylon seats have the right behavior

Anyone know what Scubapro's gray Mk5/7/10 seats are made of?

 

[happy-diver]

I can test a couple of o-rings.

How do you test Orings Boss o great one, please wow!

There was a reg manufacturer in Melbourne Australia who was not particularly pleased
when an end user packed one of his O2 emergency regs with silicone and it caught fire

Fortunately before he had placed it in the prospective recipients mouth
It was the manufacturer that took the hit to the reputation not the filler

Today I was acetylene brazing a gas manifold and did pay unnecessary
heed, regarding oxygen, just because of what divers hear, then repeat
not welders

Safety is paramount

As is my manifold

 

[iointerrupt]

Anyone know what Scubapro's gray Mk5/7/10 seats are made of?

I have some raw nylon bar stock which is the same gray color. Guess I should try that next for my seat experiments. Nylon is deeply unfun to machine though, the factory gray seats I have appear to be injection molded.

 

[Tanks A Lot]

It IS exposed to tank pressure on one side.
And lawyers.

Hah, now you are confusing me! Let's see if we can find where my thought process is wrong.

1. Take a full cylinder, no regulator attached and open the valve.
The air has to expand from the HP portion of the cylinder into ambient pressure. This happens right at the seat/orifice area of the cylinder valve. Everything after that seat/orifice of the cylinder valve will be at ambient pressure, albeit at a high velocity.

2. Take a full cylinder, with a regulator attached and open the valve.
The air from our example above now starts to flow into our regulator system. Air from the HP side of the cylinder will "fill up" the volume between the orifice of the cylinder valve and orifice of the first stage. While it is filling up that space, some of the air escapes through the first stage orifice, as the system is in the open position on an unpressurized regulator.

As it escapes through the first stage orifice it "fills up" the IP side of the system. Once that IP side reaches a certain value, the piston will get pushed against the orifice, closing it.

At no point should there have been an increase to HP levels at that upper piston O-Ring. Unless one would assume that the cavity where the piston head sits fills up to HP levels of air, before the air bleeds into the hoses and under the piston. I do not believe that would be correct. If one would picture it as an in-compressible liquid flowing step by step through the system, I understand how that conclusion could be drawn, but that is not the case with a compressible gas. A gas should spread out evenly, with the points closer to the HP portion at a much higher velocity, but not at a higher pressure. A gas does not fill up a certain area before moving on to the next, it spreads out.

To make matters more confusing, if my memory serves right, the area just past the orifice should be where the "vena contractor" sits. The point of the highest gas velocity and therefore the least pressure.

Writing this down makes me think that maybe pressure was not a reason for FKM in that area, but rather gas velocity.

Now where did I go wrong here?

 

[rsingler]

A carefully thought out response, @Tanks A Lot !
You are absolutely correct, and I didn't think my reply through. Unlike a flow- through piston, the pressure that oring sees is limited to IP.
And you also may have a lead on why they recommended FKM for the shaft. With slam opening of the tank, and tank wall particulates that are carried in the high speed gas stream, impact ignition and adiabatic compression "might" cause a fire. You and I know that's pretty improbable, but...lawyers.

Very nice drawings!