OP
Life in the face of EVO
- Thread starter lexvil
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Geo7
Contributor
Great thread. I sold the Mk11T due to not liking the HP hose being angled too much towards the diver. The MK11Evo is compact, lightweight, and has hose routing I find ideal.
One thing I do like about the Mk17 Evo mk1 though is that you can remove the diaphragm retainer with a standard wrench. It seems the Mk11 needs a propriatary tool, or does a hook spanner work?
One thing I do like about the Mk17 Evo mk1 though is that you can remove the diaphragm retainer with a standard wrench. It seems the Mk11 needs a propriatary tool, or does a hook spanner work?
OP
Yeah - 7 psi shift from full to empty tank is about right for many of SP's firsts. Pretty average balancing. But nothing a current balanced second can't handle.
As we did with the Poseidon XStream, adding a very thin shim to the base of the bias spring on the poppet may sort that out. It's on my list of experiments...
If you want rock-solid IP stability, look to Mares. They depended upon it due to their persistent use of unbalanced second stages up until the last decade. For them, 1-3psi of shift is all you'll see.
As we did with the Poseidon XStream, adding a very thin shim to the base of the bias spring on the poppet may sort that out. It's on my list of experiments...
If you want rock-solid IP stability, look to Mares. They depended upon it due to their persistent use of unbalanced second stages up until the last decade. For them, 1-3psi of shift is all you'll see.
Geo7
Contributor
It's very hard to let go of my sealed Atomics. But I find myself diving them less and less. Such a magnificently simple device, but I get SO frustrated with mushy lockup. They come that way from the factory, until I polish the knife edge. They get that way from tank particulates way before any "three-year/300 dive" service interval.
They rarely fully creep, so I don't worry about losing gas if I forget to turn the tank off for the boat ride. But the lack of crisp valve action is very distressing to me.
I've often wondered if we could change the direction of HP gas entry and seal the valve from the inside radius with a plug-type seat. It's that U-turn down the bore that's killing the knife edge.
They rarely fully creep, so I don't worry about losing gas if I forget to turn the tank off for the boat ride. But the lack of crisp valve action is very distressing to me.
I've often wondered if we could change the direction of HP gas entry and seal the valve from the inside radius with a plug-type seat. It's that U-turn down the bore that's killing the knife edge.
OP
Maybe PFA or similar. The bigger problem is maintaining reg IP balance from full to empty tank. Sealing to the ID of the piston shaft would allow you to direct HP gas almost parallel to the bore. But the decreased ID compared with the shaft diameter would completely screw up balancing.
You'd have to do differential sizing of the tip compared with the shaft. Sort of an extreme version of this:
only with a much bigger tip. That way, the tip ID could match the shaft OD.
But to do that, you'd have to do what Sherwood does with the SR2 and assemble the piston from both sides: UNscrew the shaft with fat tip from the ambient chamber side, into the piston head.
Workable, but techs could easily screw it up.
And the computerized milling to change the HP gas pathway might get a little tricky.
I'm just dreamin'.
You'd have to do differential sizing of the tip compared with the shaft. Sort of an extreme version of this:
only with a much bigger tip. That way, the tip ID could match the shaft OD.
But to do that, you'd have to do what Sherwood does with the SR2 and assemble the piston from both sides: UNscrew the shaft with fat tip from the ambient chamber side, into the piston head.
Workable, but techs could easily screw it up.
And the computerized milling to change the HP gas pathway might get a little tricky.
I'm just dreamin'.
halocline
Contributor
Not for most of the balanced piston regs; my MK25s might drop 2 or 3 PSI from 3K to 500, same for the MK15s, the MK10s do drop 7-10 (that’s one reason i’m not crazy about the MK10) and my lowly MK5s have never dropped as much as 5 PSI over that range.
But the MK11 rises 7-10 PSI, and if memory serves me, the one I worked on was closer to 10. I remember being really surprised because it’s not that difficult to make a diaphragm reg very consistent throughout the range; the old conshelfs are way better than the MK11 in that regard.
First stages have one job to do; provide stable, steady, solid IP to the 2nd stage. Is it too much to expect that a balanced 1st stage, from a premium company, does that throughout the supply range? Not in my mind.
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