Life in the face of EVO

[lexvil]

7 psi is irrelevant with good second stages

 

[Geo7]

There must be a trade-off between IP stability through the tank pressure range, and some other variable? Perhaps flow rate? I could imagine Scubapro sacrifying performance in several areas, in order to remain the flow rate king...

 

[lexvil]

I started thinking (dangerous) that I forgot to tap the purge after charging it on the lower pressure tank so I just rechecked it

 

[Umuntu]

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 balancing.
You'd have to do differential sizing of the tip compared with the shaft. Sort of an extreme version of this:
View attachment 872908
only 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 into the piston head.
View attachment 872910
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'.

When I read your earlier post I thought that you were talking about something like a balanced version of a MK2 but with a through piston flow path. I’m confused

 

[buddhasummer]

I’d be curious if any of the MK11 variants have better IP consistency throughout the supply range. The one MK11 that I worked on some years back rose almost 10PSI from 3K to 500 PSI. Not exactly a balanced 1st stage if you ask me.

Ditto MK17 IME. I had I've IIRC that had a 15psi swing (?) not positive on that number but it was high, I was surprised.

 

[rsingler]

Some of the swing in a diaphragm can be ameliorated by a quick removal of the HP poppet carrier and re-lubing the oring and poppet shaft. Some of it is inherent in design. Some of it worsens as the tiny bias spring fatigues. In that case, a new spring will lessen the spread, and as I suggested above, I'm going to experiment with shimming that spring to improve the stability. That does work on the Poseidon Xstream.
For a piston, you can change out the shaft oring and add extra lube, though that won't last long. Actually, that was one of the cool things about the DGX piston XTRA. The reg body had a second sealing shaft oring that kept ambient seawater from washing away the lube. Two o-rings meant slightly more friction, but the lube reservoir persisted.

 

[rsingler]

When I read your earlier post I thought that you were talking about something like a balanced version of a MK2 but with a through piston flow path. I’m confused

Here's a crude drawing...

 

[buddhasummer]

Are you a gynaecologist Rob

 

[BoltSnap]

Are you a gynaecologist Rob

He just came out of a gyno surgery. He had a good angel in front row

 

[halocline]

Ditto MK17 IME. I had I've IIRC that had a 15psi swing (?) not positive on that number but it was high, I was surprised.

It’s the same seat/poppet/balance chamber arrangement so that doesn’t surprise me.