Most well known "standard" regulator

[OMyMyOHellYes]

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So what your saying is if I use this then I should probably get a balanced first stage ?

You should only be on that thing for a few minutes, and as you are going upwards while on it, each breath would get easier AND it **should** never happen that you would be on that Air2'ish regu-flator in any case.

Me, personally, and you didn't ask me, but if I was on a MK 2 first stage, that would be the least of my worries at that time.

 

[xanaphyst]

You should only be on that thing for a few minutes, and as you are going upwards while on it, each breath would get easier AND it **should** never happen that you would be on that Air2'ish regu-flator in any case.

Me, personally, and you didn't ask me, but if I was on a MK 2 first stage, that would be the least of my worries at that time.

Yeah that makes perfect sense now that you say it !!

 

[NothingClever]

Yes, I was using a long hose wrapped around my torso and neck. The crew was in a hurry, I still had my camera and was trying to hand it off and they just grabbed me by the long hose and my bad arm and yanked me in while I was still trying to doff my gear being hindered by also still having my camera.

That sounds totally miserable. I might’ve blown a gasket with the crew.

 

[halocline]

In a post nuclear event, what you are saying about the mk2 maybe of value, but in our reality now, the MK2 doesn't have much advantage over the simple mk11.

That depends on how much you value the ability to hold up between rebuilds. First, I found that the MK11 is not much better balanced than the MK2, although this was about 10 years ago so they may have improved it since then. The one I had rose about 12 PSI over the supply range. The MK2 drops about 15 PSI over that same range. Second, my MK11 started creeping about a year or so after rebuilding; not much, but add that to the inherent IP rise and you could be looking at a free flow near the end of dives. My MK2 has never creeped, ever. I used it for a few years when I first started diving, then let it sit for several years, brought it back into service as a pony regulator (which I only used a couple of times) then filled tires with it for at least ten years, and then decided to oxygen clean it and turn it into 100% O2 deco reg. Before I took it apart to do so, I checked IP and, as always, rock solid lockup. That’s with one service in 20 years.

There’s something to be said for a design so proven and so simple that it can literally go decades without attention and still work. And it’s not like the flow characteristics are bad; on a full tank, the MK2 flows around 90 SCFM, or the equivalent of emptying an AL80 in under one minute.

I also think it’s an ideal deco reg. Not just acceptable, but ideal. There’s almost no combustible material in the HP path; a total of 2 o-rings (plus the tank or DIN o-ring). One of those seals the retainer, and the other seals the HP port plug. And the seat is a tiny plug that is available as O2 compatible.

There’s nothing wrong with the MK11, just like the vast majority of commercially available regulators sold by reputable companies, they are fine for virtually any kind of recreational diving.

 

[Mobulai]

And the seat is a tiny plug that is available as O2 compatible.

Is there a specific source you know that sells o2 compatible mk2 seats — I’m on the hunt but I only find the standard seat

Or do you use the rebuild kit as a whole?

 

[lexvil]

I like the hose routing better on 90° type regulators over the straight out type like the titan and MK 2, newer MK 11 is a great reg and it and the 17E2 are proving to be the best first stages I’ve used. Just because someone can get by with low performance doesn’t mean the should

 

[Nemrod]

The Mark 2 Evo is not low performance at 90 cfm (500 psi) to109 cfm (3000 psi). The AL Conshelf/Titan/Core/Helix/Legend first stage is only something like 75 cfm at 3000 psi. The first stage is not the restriction in air delivery, even for a Mark 2E or lesser regs like the Legend/Conshelf design ubiquitous to AL. A G250/G260 second stage can flow up to 64 cfm, a C370 is 57 cfm. So, two G260s on open flow could exceed the flow capacity of a Mark 2E, hmmm. BTW, the old Conshelf-Legend first stage is very tightly balanced, more so than a Mark 11 which has up to about a 12-15 psi swing from 3000-500 psi. But, I see more IP drop per breath and slower recovery with the AL first stage than with the Mark 2E. Why, the Mark 2E has a larger and less restricted volcano orifice. It is larger in area and is not occluded by the pin, same for the Mark 11, which also has a pin running though it.





Let's look further. A male human in good fitness at moderate exercise levels would use 3.5l per breath and take 30 bpm which converts to 3.5 cfm. The air volume does not change with depth, only density. Elite athletes can reach 60 or more bpm and ventilate 180 lpm (6.4cfm). Again, the volume at depth does not change, just the density.

A Mark 2E can flow more air than a single G260. A Mark 11/17/19 (which is not especially well balanced and does not matter with a balanced second stage) can flow up to 195 cfm thus exceeding the flow rate of two G260s. Hmm, but two humans, assuming they are elite athletes working at their maximum effort would consume 12.8 cfm. That would be emptying an aluminum 80 (77 cf) in about 6.5 minutes at the surface or 1.6 minutes at 4 atm.

Higher performance first stages should have less IP drop and quicker recovery under flow. Thing is, none are working at or even near the maximum capacity since the human in the equation is the limiting parameter. I do not see but slightly more IP drop and slower recovery with a Mark 2E vs my Mark 25 per breath. I do see more IP drop/Delta between a gauge at the first stage and one at the second stage with a "long" hose vs a "short" hose. Does this matter, apparently not.

Less is more, minimalism, and that includes the parts count of my first stage . How much air flow capacity does a scuba diver need? Exactly enough to satisfy their tidal volume per breath at their working rate which is rarely more than 30 bpm. So then 3.5 cfm times two divers equals 7 cfm.

 

[Eric Sedletzky]

I don't mind the hose routing on the radial style regs like a MK2 or Conshelf.
Looking at it from behind, the HP port is on the lower left at about 7:00, the primary is at about 4:00, the bungeed second is at 2:00, and the Lp hose for the bc is at 10:00 or 11:00.
They all seem to line up fine.

 

[lexvil]

The Mark 2 Evo is not low performance at 90 cfm (500 psi) to109 cfm (3000 psi). The AL Conshelf/Titan/Core/Helix/Legend first stage is only something like 75 cfm at 3000 psi. The first stage is not the restriction in air delivery, even for a Mark 2E or lesser regs like the Legend/Conshelf design ubiquitous to AL. A G250/G260 second stage can flow up to 64 cfm, a C370 is 57 cfm. So, two G260s on open flow could exceed the flow capacity of a Mark 2E, hmmm. BTW, the old Conshelf-Legend first stage is very tightly balanced, more so than a Mark 11 which has up to about a 12-15 psi swing from 3000-500 psi. But, I see more IP drop per breath and slower recovery with the AL first stage than with the Mark 2E. Why, the Mark 2E has a larger and less restricted volcano orifice. It is larger in area and is not occluded by the pin, same for the Mark 11, which also has a pin running though it.





Let's look further. A male human in good fitness at moderate exercise levels would use 3.5l per breath and take 30 bpm which converts to 3.5 cfm. The air volume does not change with depth, only density. Elite athletes can reach 60 or more bpm and ventilate 180 lpm (6.4cfm). Again, the volume at depth does not change, just the density.

A Mark 2E can flow more air than a single G260. A Mark 11/17/19 (which is not especially well balanced and does not matter with a balanced second stage) can flow up to 195 cfm thus exceeding the flow rate of two G260s. Hmm, but two humans, assuming they are elite athletes working at their maximum effort would consume 12.8 cfm. That would be emptying an aluminum 80 (77 cf) in about 6.5 minutes at the surface or 1.6 minutes at 4 atm.

Higher performance first stages should have less IP drop and quicker recovery under flow. Thing is, none are working at or even near the maximum capacity since the human in the equation is the limiting parameter. I do not see but slightly more IP drop and slower recovery with a Mark 2E vs my Mark 25 per breath. I do see more IP drop/Delta between a gauge at the first stage and one at the second stage with a "long" hose vs a "short" hose. Does this matter, apparently not.

Less is more, minimalism, and that includes the parts count of my first stage . How much air flow capacity does a scuba diver need? Exactly enough to satisfy their tidal volume per breath at their working rate which is rarely more than 30 bpm.

Actually didn’t mean to imply the MK 2 was low performance, it is truly the cockroach of regulators, when the aliens arrive in 20 million years to ponder what sort of self destructive species could destroy their planet yet still have made the ScubaPro MK 2 which found in the rubble in still functioning condition…

I don’t like the hose routing. Life is to short to use clunky second stages

 

[Eric Sedletzky]

The Mark 2 Evo is not low performance at 90 cfm (500 psi) to109 cfm (3000 psi). The AL Conshelf/Titan/Core/Helix/Legend first stage is only something like 75 cfm at 3000 psi. The first stage is not the restriction in air delivery, even for a Mark 2E or lesser regs like the Legend/Conshelf design ubiquitous to AL. A G250/G260 second stage can flow up to 64 cfm, a C370 is 57 cfm. So, two G260s on open flow could exceed the flow capacity of a Mark 2E, hmmm. BTW, the old Conshelf-Legend first stage is very tightly balanced, more so than a Mark 11 which has up to about a 12-15 psi swing. But, I see more IP swing and slower recovery with the AL first stage than with the Mark 2E. Why, the Mark 2E has a larger and less restricted volcano orifice. It is larger in area and is not occluded by the pin, same for the Mark 11, which also has a pin running though it.



Let's look further. A male human in good fitness at moderate exercise levels would use 3.5l per breath and take 30 bpm which converts to 3.5 cfm. The air volume does not change with depth, only density. Elite athletes can reach 60 or more bpm and ventilate 180 lpm (6.4cfm). Again, the volume at depth does not change, just the density.

A Mark 2E can flow more air than a single G260. A Mark 11/17/19 (which is not especially well balanced and does not matter with a balanced second stage) can flow up to 195 cfm thus exceeding the flow rate of two G260s. Hmm, but two humans, assuming they are elite athletes working at their maximum effort would consume 12.8 cfm. That would be emptying an aluminum 80 (77 cf) in about 6.5 minutes at the surface or 1.6 minutes at 4 atm.

Higher performance first stages should have less IP drop and quicker recovery under flow. Thing is, none are working at or even near the maximum capacity since the human in the equation is the limiting parameter. I do not see but slightly more IP drop and slower recovery with a Mark 2E vs my Mark 25 per breath. I do see more IP drop/Delta between a gauge at the first stage and one at the second stage with a "long" hose vs a "short" hose. Does this matter, apparently not.

Less is more, minimalism, and that includes the parts count of my first stage . How much air flow capacity does a scuba diver need? Exactly enough to satisfy their tidal volume per breath at their working rate which is rarely more than 30 bpm.

I laugh when I hear people tell me that such and such 1st stage breathes better than so and so 1st stage.
Any half way decent balanced second stage will be able to compensate for the ever so slight variances in performance differences in different style first stages. Unless your first stage is some antique diaphragm with a very old crusty and inflexible diaphragm and you happen to be very deep sharing air huffing and puffing would you ever encounter a problem with not enough flow.
People misunderstand that all the first stage needs to do is drop tank pressure down to a steady 135 ish intermediate pressure and ALL your imagined breathing performance issues, whoas, or triumphs after that will be in the second stage. Type, style, design, of the second stage is where all of it is at.
You could take a G250 and stick it on the suckiest 1st stage and the unit will breathe great. You could put the suckiest second stage on the hottest 1st stage like a MK25 or Atomic and it will be absolutely terrible.
Let's get over the 1st stage debate already.