Question Skipping 1st stage Maintenance?

[Mobulai]

Btw, the service manual for mk25E specifies: 9 to 10 bar

Don’t forget to let it sit for an hour or 2 after cycling, then see if IP changed, ideally once more overnight — that’s the sign of good lockup/no creep

 

[Mobulai]

The ONLY source of IP creep in a piston is the seat/ knife edge interface.

That lesson didn’t stick to my head yet :/
Maybe I’m due for a refresher class

 

[Pearlman]

Ok, had to get to a computer to view schematics

To answer your 1st q, no
The washer can be dropped out for the sale of IP

But the 2nd q is the critical one:
That stem oring is a HP interface, so, if it has a scratch I would expect IP to creep drag (if not now, soon); and maybe eventually a big leak, or worst case, tearing
It might drag with higher friction (causing a slow IP response— something that the mk20/25 are known to have rather quick), or maybe even catch a grit of sand and scratch the piston (but maybe very far fetched)

Better get another unscratched oring (the 01-050-138 is a 2-011 duro85), or if you can’t source it on its own then another service kit and use that

To be clear the o-ring is perfectly fine. It’s the inner/topmost plastic bushing that is referred to as plain old “ring” in the schematic on the hp side and I don’t think sand or grit will get past the hp o-ring from the ambient side. However I saw another doc that referred to it as a “superglide” sleeve so I was thinking it matters as much as a 2nd stage lever and diaphragm coefficient of friction ( which you have elaborated better than me ). That topmost sleeve always seems to remain stuck inside the body and I ended up scratching at it while trying to hook it repeatedly with the brass tip and push it down. I’ll try removing the shim/washer first and hopefully redo the seat push-down on the spring and piston edge that lies just below the adjustment spring as well.

Yeah I get that ultimately the source of the creep would be improper sealing of the piston edge and seat. I think I turned the adjustment screw in haste once before shutting off the valve and depressurising the reg in between multiple attempts at tuning. Hope that didn’t make it worse.

It’s definitely out of my comfort zone if the swing IP is close to 9.8 bar although maybe it’s within “spec” for those that wish to tune their regs for some special reasons only they can justify.

 

[Mobulai]

Dammit I misunderstood , my mind just read oring

bushing that is referred to as plain old “ring”

i suspect these would be alright if the got scratched

It’s definitely out of my comfort zone if the swing IP is close to 9.8 bar although maybe it’s within “spec” for those that wish to tune their regs for some special reasons only they can justify.

I understand/agree of that’s the min you can get on the adjustment
Maybe it’s the knife edge that needs some dressing

 

[Pearlman]

Btw, the service manual for mk25E specifies: 9 to 10 bar

Don’t forget to let it sit for an hour or 2 after cycling, then see if IP changed, ideally once more overnight — that’s the sign of good lockup/no creep

9.2-9.8bar is the official max on the Scubapro docs…. So with swing+creep and after lockup in an extended test, 9.8 may be acceptable … looking forward to redoing the build tomorrow AM!

 

[elmo]

It’s definitely out of my comfort zone if the swing IP is close to 9.8 bar although maybe it’s within “spec” for those that wish to tune their regs for some special reasons only they can justify.

I’m also new to servicing my regs - MK17 first stages mostly, so much of your experience isn’t relevant to me but IP is IP. If the manual says IP should be 9-10 bar, what’s wrong with 9.8?

 

[rsingler]

I’m also new to servicing my regs - MK17 first stages mostly, so much of your experience isn’t relevant to me but IP is IP. If the manual says IP should be 9-10 bar, what’s wrong with 9.8?

IP is a dynamic pressure. It drops during inhalation, so your second stages need to be able to handle the drop.
It typically rises when the valve sits. While we'd like to believe the seal is perfect, it isn't. So it's not atypical for it to rise 1-3 psi. Starting at 9.8bar puts you closer to the max. The max isn't absolute, but also gets you closer to where a second stage might freeflow. Typically, I'll run IP around 135psi/9.3 bar.

Pistons are typically a little worse than diaphragms in maintaining a crisp seal, and often have 3-7psi of "IP Drift". @Pearlman 's approach is pretty reasonable.

 

[Pearlman]

Annnd … we have lockup! At the desired reading …
After an hour the creep is exactly on the middle line so maybe 1psi approx…

Things I did - removed the washer/shim from the spring bush and inserted the ambient chamber body into the main body over the piston bullet (in reverse rather than turn the piston upside down) as suggested and also paid special attention to ensure the adjusting screw was threaded in all the way before putting the seat retainer and torquing it. I think it wasn’t just the shim but all of the above that made it work!

Had to fine tune the adjusting screw to dial down the IP from almost 10 initially down by .6 bar to 9.35 bar now actually.

Thanks to everyone for the tips and suggestions!

 

[CG43]

It doesn't mean much. Scubapro has lousy environmental seals. They develop an air pocket after 3 months because they don't hold a vacuum. So with a little air in there you have to compress the bubble before the reg begins to respond to depth. The reg is off maybe 3-10 feet in depth response, which means that absolute IP may lag 1.5 to 5 psi, and so the IP your second stage sees may drop the same amount. Your second stage won't care.

No ! there is no change in IP because an air pocket .

The pressure to compress the bubble is translated through the air chamber to the first stage diaphragm and thus increases the IP .
As long as it is not an overcompensated 1st stage, it does not matter whether a mechanical force is used via a transmitter or by an increase in pressure in the drying chamber. The force acting on the first stage diaphragm is the same.

The bad thing that can happen with a dry chamber is that water comes in . This promotes corosion and facilitates icing.
With a first membrane stage, I think it makes the most sense to open the spring space as far as possible to the water, as Poseidon does with the X-steam and Jetstream. Rinsing , drying and conducting heat from the water are exellent .

 

[Pearlman]

Is there such a thing as a valve shutdown and IP test? Since I was heading out and didn’t want anything blowing up and losing all my gas I shut down the valve but left it pressurised for 4 hours. I maybe wrong but IP seems to have crept up a notch by 0.5 to 1psi. Didn’t photograph the IP gauge while leaving so can’t be sure. So the total creep in 6hrs is about 2psi now…but how can IP creep when the tank valve is shut down? Unless it’s just parallax error …