Free flowing Mares abyss

[lowwall]

If the backup didn't freeflow then it wasn't a major first stage failure. The most likely causes were either:

- bit of sand or grit that kept the 2nd stage valve from completely closing.

- first stage intermediate pressure (IP) that was higher than spec. If it went high enough, it would overcome the second stage valve spring pressure and start flowing.

The only way to be sure which it was is to check the IP value on the first stage. You do this by attaching an IP gauge to the LPI hose from your first stage and opening your tank valve. What you want to see is something in the range that Zef showed above. And then you wait. The IP might increase a tiny bit in the first minute or two but should be rock solid after that. A gradual increase in the IP pressure after that is what we call IP creep. You'll need to get the first stage serviced if the initial IP is too high or the IP creeps.

It's really worth getting an IP gauge. A basic one like the one pictured below is $10-$20 and can save you from paying for an unnecessary service or an aborted dive.

 

[lowwall]

That decreased clearance is one reason why some cavers prefer downstream (unbalanced) seconds: they're dirt simple, and there are only two moving parts: lever and poppet. Tuned properly (and regularly) they are perhaps more reliable than a balanced second stage when paired with a balanced first.

The Mares Abyss second is unbalanced.

I’m curious to know if I should invest in a newer, more high end reg. ( paranoia).

Your second stage is high end. Mares still sells versions of it as part of their top end Abyss Navy II and XR - DR regsets. We don't know what your first stage is, but unless it's an old MR12, it's very likely worth keeping.

 

[rsingler]

The Mares Abyss second is unbalanced.

Ah! Right you are. I'd forgotten that. No idea what was responsible then, if it wasn't IP related.

As for the MR12, my son and I overhauled one a couple of months ago just for his practice. And it had ZERO IP change from 300 to 3000 psi tank pressure. Pretty good balancing design, I'd say.

 

[jf3193]

If the backup didn't freeflow, that slightly decreased the chances that it was excessive 1st stage IP causing the freeflow. But most octos (not mine) are tuned more stiffly than the primary second stage, so it still could have been IP induced freeflow (too much input pressure for the valve setting).

But another possibility for an out-of-the-blue freeflow is the valve sticking open due to a mechanical factor. The first thing I'd do is disassemble the valve and look for a grain of coral stuck in the tiny crevice where the poppet goes into the balance chamber. That decreased clearance is one reason why some cavers prefer downstream (unbalanced) seconds: they're dirt simple, and there are only two moving parts: lever and poppet. Tuned properly (and regularly) they are perhaps more reliable than a balanced second stage when paired with a balanced first.

I just thought of something. It happened when I was taking my self reliant class. I had been switching from 2nd to pony bottle multiple times during a few dives that day. Im wondering if some debris/sand/coral happened to get into my 2nd. My instructor was really good at taking my mouthpiece out at random to test stressful situation diving.

 

[lowwall]

As for the MR12, my son and I overhauled one a couple of months ago just for his practice. And it had ZERO IP change from 300 to 3000 psi tank pressure. Pretty good balancing design, I'd say.

I agree. But the first generation doesn't have a replaceable HP seat, so if it's not sealing well it's time to scrap it.

Edit: Or give DIY a try, see Free flowing Mares abyss below.

 

[jf3193]

Could you snap and post a picture of your 1st stage?

Almost all the Mares diaphragm model 1st stages are set to the IP range I indicated in my previous post.

From the 2001 Mares service manual:

Table of First Stage Intermediate Pressures
Model PSI BAR
Ruby (this is an MR22 variant) 142-148 9.8-10.2
V32 (later became the MR32) 142-148 9.8-10.2
MR22 142-148 9.8-10.2
MR16 142-148 9.8-10.2
TI Planet (this is a V16 variant) 142-148 9.8-10.2
V16 (later became the MR16) 142-148 9.8-10.2
MR12 142-148 9.8-10.2
V12 (later became the MR12) 142-148 9.8-10.2
MR12 II° 137-142 9.5-9.8
R2 (with tank at 2900 psi/200bar) 142-152 9.8-10.5 (this is a piston type 1st stage)
MR10 (with tank at 2900 psi/200bar) 123-130 8.5-9.0 (I am not familiar with the MR10 1st stage, but MR typically implies a diaphragm type 1st stage in the Mares lineup)

-Z

 

[jf3193]

here ya go

 

[lowwall]

here ya go

That's either a 32 or post-2008 MR22. Maybe Zef can tell the difference. They are basically identical internally and have the same spec IP range of 142-148psi 9.8-10.2bar (or kg/cm2, same thing at this level of measurement).

I think sand in the second stage is the more likely explanation, but it's still worth getting an IP gauge and checking it out just to be sure.

 

[rsingler]

I think sand in the second stage is the more likely explanation, but it's still worth getting an IP gauge and checking it out just to be sure.

Well, jamming a downstream second with junk is pretty unusual. Maybe a large grain catching in the lever? That's why we're taught to bang it hard on our thigh in the event of a freeflow. I'm going to guess 1st stage IP.

Fun discussion!

 

[rsingler]

...the first generation doesn't have a replaceable HP seat, so if it's not sealing well it's time to scrap it.

It's time to drag out the Micromesh and a pencil, and polish it!
Conshelf, with non-replaceable orifice deep in the reg body. Before and after: