Anyone tried running a 2nd stage from original MK15/MK15.5 1st stage reg?

Drmike

Hi,

I was wondering if the small simple sherwoods used in the MK15 series could provide enough flow at depth to run a 2nd stage from it?

Has anyone tried this?

Cheers
Mike

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Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

teksimple

Mike -

Good question. I am interested in that as well. In my case I was thinking that I could feed a 2nd stage directly from the Whitey valve that I have plumbed in for offboard diluent. I am thinking that at depth the piping size restriction as much as the 1st stage gas delivery rate would be limiting factors in getting an easy breath. But I figure if I am depending solely on a partially used 21 cubic foot diluent bottle at significant depth for bailout, I have got other problems than just breathing comfort.

Drmike

For sure I wouldn't rely on a half full 3L dil tank as a bail out option. My OC/CC valve is my initial/primary bail tool. When the shit hits the fan I would turn the handle and go. The OC/CC is plumbed into my off board bail tank using a QC.

That works fine, but on occasions I have to unclip the off board in order to squeeze through holes etc. In this case, albeit momentarily, I loose my OC connection to the OC/CC valve so have no 'immediate' access to bailout.

What I was thinking was to plumb in a valve so I can temp switch the OC/CC reg to come off the onboard for times that I have to unclip the offboard, or when I don't have the off board (e.g. when Ive passed it up to crew when surfacing,
handed it to a diver in need, ect) The small on board would not be able to
free flow under normal use as the valve would isolate it from the OC/CC 2nd
stage at all times, other than when I would need to use it. Another small
benefit would be access to a little extra gas if I do have to bail to OC.

So Im adding another 3 way valve as a additional failure point - but I'm gaining the continuity of the bail to the oc/cc valve and immediate access.


I have had 2 experiences that made me appreciate a need for this.

One about a year ago I had finished a hard dive and was passing up my stages in rough seas. I had passed them all up and was just about to crawl up the bouncing ladder when the boat lurched up in a big swell and hit me full on in the face. I lost vision, lost the boat and the loop filled with water. I was slightly negative, below the surface and had to breathe.

I instinctively came off the loop by turning the oc/cc valve - but no off board plumbed in as Id just passed it up!! .....Im still underwater still cant see the boat is bouncing up and down above my head someplace so I dare not just ascend immediately - I had to try to swim away before coming up.

Another time squeezing out of a wreck I had to drop my stage and push it and the rebreather out in front of me through the worlds smallest hole. To do this I had to unplug the stage and push it through then take off the unit (by rolling it over my head whilst keeping the mouthpiece in) As I was doing this it struck me that should the WOB be too high with the rig infront of me, or should the twisting of the hoses cause a loop flood, then I would not be able to breathe!...

These two cases (and one more when I had to pass my stage to a OC diver) made me realise that a simple extra valve would make things a lot safer. Sure the little 3L is not going to last long but its amazing how time flys when you cant breathe and how even 1 or two minutes can seam like a lifetime of time to sort out a problem in if you can.

Of course a proper isolation valve would be needed.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment

teksimple

Yep, a T and a check valve! Since I am like 12000 kilometers away from my unit, it is hard to visualize the setup without it in front of me. Please post again if you come up with something that works for you.

The question still remains...how decent are those 1st stages?

abowie

As long as the first's IP is appropriate to run a normal 2nd (about 10bar/140psi) it'd be worth trying.

Why not pop one on and give it a try on a dive and see?

PS "Yeah but nah but yeah but nah but..." Did you see the episode with her on rollerskates in a pink bikini? You don't get THAT at the "4 Floors of *****s" :-)

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Andrew Bowie

Rebreather-friendly Buddy

SteveL

Dr M - Slightly off topic but when you are plugging and un plugging u/w are you worried about water getting into the System. I too have QC 6 swagelok fittings on the 15.5 and notice that they would hold alot of water if they were unplugged u/w. So if you then start pumping this through the filter and other plumbing in the system - there will be green crap in the system in no time flat. Some going through the second stage so what - but I have to say cleaning all that stainless tubing would be a pain in the...

Thoughts???

If you had other connections albeit more failure points then at least you wouldnt get water in the system.

Steve

koputai

Steve, the piping is a VERY limiting factor as far as o/c gas flow goes.
So, you think, stuff it, I'll just run the 2nd stage directly from the 1st stage reg. But, your 1st stage is running at 18 bar, so getting a 2nd to hold back that sort of pressure is very unlikely.

Cheers,
Jason.

hoppyinca

even I as a newbie Mk15 diver know that the 1st on one of these units is far from a high end reg...

But I must agree that as long as the IP is high enough there is no reason it should not work in a pinch.

as for the problem of it being too high and the 2nd not being able to hold back the pressure, this would not be a problem if the 3-way whitney valve is used (the 2nd will be isolated until needed).

I think another more simple option would be to run the 2nd stage directly form the 1st, and have an "in line shut off"...

I too have been contemplating this modification, though I have a butt mount on order for a 13cuft bottle...

Dr. M would a butt mount solve the disconnecting issue... except in the instance of handing off...

hoppyinca

koputai

No, I've tried it. As soon as you apply dil pressure to the o/c 2nd stage it free flows like buggery.
All you guys who picked up the Ebay Mk15's, actually most 15's and some 15.5's out there, it may well work running the 2nd straight off the 1st, as your dil regs are running at 8 bar, not 18 bar like ours.

Cheers,
Jason.

sadave

Just thinkin alound Jason, but I know with the Sea Hornet Hookah first stages I used to use when working in Pt Lincoln (commercial diving), the only difference between them and a normal 2nd stage was a stronger spring.

Now I know these are still operating nowhere near 18bar, but it could be something worth thinking about, if you wanted to start playing with stronger springs in one of these 2nd stages???

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