Scubapro Mk10 - low intermediate pressure

[rsingler]

Which, for those reading along, is exactly why a second stage seat taking a set begins to gently freeflow three months after service.
The new groove in the low pressure seat is effectively the same as backing the orifice out a few thousandths, and the reg begins to leak.
To prevent this, your shop helpfully adjusts the orifice in a few thousandths more than necessary to seal, at service. This detunes the reg, and makes it harder to breathe than it might have, just to save you from coming back to the shop complaining about the expected leak.
(Unless you own an Atomic )

 

[shurite7]

Which, for those reading along, is exactly why a second stage seat taking a set begins to gently freeflow three months after service.
The new groove in the low pressure seat is effectively the same as backing the orifice out a few thousandths, and the reg begins to leak.
To prevent this, your shop helpfully adjusts the orifice in a few thousandths more than necessary to seal, at service. This detunes the reg, and makes it harder to breathe than it might have, just to save you from coming back to the shop complaining about the expected leak.
(Unless you own an Atomic )

This is very true. Something I learned when I first started servicing regs. Well said rsingler.

 

[Andrew Dawson]

Which, for those reading along, is exactly why a second stage seat taking a set begins to gently freeflow three months after service.
The new groove in the low pressure seat is effectively the same as backing the orifice out a few thousandths, and the reg begins to leak.
To prevent this, your shop helpfully adjusts the orifice in a few thousandths more than necessary to seal, at service. This detunes the reg, and makes it harder to breathe than it might have, just to save you from coming back to the shop complaining about the expected leak.
(Unless you own an Atomic )

Specifically to an MK20/25...one would set IP low...like 125psi or so...so that at the 3mo mark and beyond, it would be at the target IP for the main duration of the reg's service interval between rebuilds?

Any issue to setting it at say 120psi if you wanted the main duration of the service interval to be in the lower IP realm? If diving cold water, I would assume...a lower IP is more desirable to help stave off icing a little bit more. No?

 

[shurite7]

Any issue to setting it at say 120psi if you wanted the main duration of the service interval to be in the lower IP realm? If diving cold water, I would assume...a lower IP is more desirable to help stave off icing a little bit more. No?

I've found it hasn't been necessary to set the IP below 125 for the cold murky lakes around here, including diving in the winter. I set my Mk25s to 130 or 135 with no issues.

 

[Andrew Dawson]

I've found it hasn't been necessary to set the IP below 125 for the cold murky lakes around here, including diving in the winter. I set my Mk25s to 130 or 135 with no issues.

That is what I have had for many years...without issues....but, of course, read on the internet about folks with unsealed piston regs that are "nuts" to dive in cold water [below 50F]...so...I figured, I might drop IP a bit and give a little extra margin. The lakes and ocean around my area do not drop below 40F except maybe once in a few decades.

 

[rsingler]

Specifically to an MK20/25...one would set IP low...like 125psi or so...so that at the 3mo mark and beyond, it would be at the target IP for the main duration of the reg's service interval between rebuilds?

I've found that the small rise in IP with a first stage usually occurs in the first few hundred cycles as the seat takes a set. In other words, one day of diving or still in the shop if you cycle your regs after service.
The three month comment only applies to softer rubber seats in the second stage, that develop a deeper and deeper groove as the orifice presses against the seat in storage. You can avoid that by keeping the purge button depressed a little in storage, and a few Scubapro regs have a purge button lock (G260, for example) that keep the orifice off the seat and greatly extend seat life.
Atomic, as alluded to above, has a spring loaded orifice that backs away from the seat when unpressurized.
For my other regs, I use a 1/2" length of 1/2" Schedule 40 PVC pipe, which I center in the button and depress with a little length of coat hanger wire hooked in the faceplate, or ribbon tied around the reg and PVC combo, to depress the button in storage.

The issue of running low IP's for cold water as commented on above, is separate. I wouldn't argue with that, and might even go below spec with a balanced second stage. Say 115 psi even, for near-freezing water. But I'd leave the real recommendations to the real cold water divers. California is balmy at 52°F.

 

[Open Ocean Diver]

Hey rsingler, question my Atomic with a medium breath IP will dip to 110 quickly recover to 133, at 110 mag will read 1.8 after recover .9. is this IP profile ok normal operation?

 

[rsingler]

Hey rsingler, question my Atomic with a medium breath IP will dip to 110 quickly recover to 133, at 110 mag will read 1.8 after recover .9. is this IP profile ok normal operation?

That performance is a little off, IMO.
I just checked my T2 and got the following numbers:
Static IP: 135
Full purge dynamic IP: 116
I'm not sure what a magnehelic reading at 110 means, unless you have an adjustable regulator to provide varying IP's to the second stage, because cracking effort is an almost static measurement.
So I don't really understand what gave you 1.8".

However, I do have a variable regulator for checking second stages and here is the performance of the excellent balancing of the Atomic at IP's from 135 down to 65 PSI:
Cracking effort:
135 = 0.9" (I tune light!)
125 = 0.95"
115 = 1.2"
105 = 1.4"
95 = 1.5"
85 = 1.6"
75 = 1.7"
65 = 1.8"

An Atomic second should not have that much degradation in performance with that little change in IP. Similarly, the dynamic IP drop of your first stage is slightly more than I would have expected. It could be friction in a degrading HP Oring, but that's just a guess. As for the second stage number, I'd really need to know more about what you were measuring when your IP was stated to be 110.

Either way, maybe time for a service.

 

[rsingler]

I've found that the small rise in IP with a first stage usually occurs in the first few hundred cycles as the seat takes a set.

I realize that I didn't give a very complete answer. It IS possible to have a drop in IP immediately after service, but for one reason only: If the seat to knife edge interface is imperfect, the IP may creep due to leakage at that seal until there is enough intermediate pressure to force the two parts together. That higher IP will disappear after a few hundred cycles because your leak has disappeared. That drop in IP is a separate mechanism from what I was speaking of before. The drop in IP, as stated above, is from the set in the seat , as opposed to a leak. Two different phenomena.

 

[Andrew Dawson]

YES! I forgot about the 1/2" PVC pipe purge valve pressing LP seat protector...I will surely build that for the next time these regs get built...Now...can I put a seat protector diaphragm cover [Say from an R380] on a G1 or G2 S600?