MK2 overhaul question

[dumpsterDiver]

This is an honest question.. I don't know the answer..but... does 2 or 5 or 8 psi make any discernable difference in the performance of the regulator with respect to WOB? Obviously, changing the IP may require an adjustment in the second stage seat, but does a few psi in the intermediate pressure matter?

 

[bl6394]

This is an honest question.. I don't know the answer..but... does 2 or 5 or 8 psi make any discernable difference in the performance of the regulator with respect to WOB? Obviously, changing the IP may require an adjustment in the second stage seat, but does a few psi in the intermediate pressure matter?

The honest answer is that while I'm an engineer - BS Applied Physics / MS Comp Sci - I have little basis for an opinion.

The second stage is designed with an optimal input IP of 145. Higher IP and the second stage may be more likely to free flow and the first stage / second stage may be colder due to greater adiabatic cooling. Lower IP and the second stage may not be as performant as the manufacture desired.

But I am not a scubapro engineer - and have not I hooked these regulators up to a test harness and evaluated all of the consequences (performance , reliability, durability) under different conditions of (depth, temperature, flow rate) when using a non-standard IP. The most prudent choice as a technician is to tune the regs to factory specs. If I return a regulator to a customer - performing as the factory intended - my liability for that service is minimal.

 

[BIGJACK]

It's an older reg, an ebay special, and I'm not sure about the age of the schematic. It shows a spacer under the yoke and a shim at either end of the spring. I understand how shims work, the drawing called them washers and showing two of them lead me to believe they were a permanent part of the reg. The tank pressure during testing was about 2000, so I guess the IP isn't that far off, maybe two shims. I plan to use a balance 2nd and mainly use it in shallow lakes and rivers. I have two MK 20's paired with G250's and G200B's for most diving. Again, thanks for the replies.

 

[BIGJACK]

It's an older reg, an ebay special, and I'm not sure about the age of the schematic. It shows a spacer under the yoke and a shim at either end of the spring. I understand how shims work, the drawing called them washers and showing two of them lead me to believe they were a permanent part of the reg. The tank pressure during testing was about 2000, so I guess the IP isn't that far off, maybe two shims. I plan to use a balance 2nd and mainly use it in shallow lakes and rivers. I have two MK 20's paired with G250's and G200B's for most diving. Again, thanks for the replies.

 

[bl6394]

It's an older reg, an ebay special, and I'm not sure about the age of the schematic. It shows a spacer under the yoke and a shim at either end of the spring. I understand how shims work, the drawing called them washers and showing two of them lead me to believe they were a permanent part of the reg. The tank pressure during testing was about 2000, so I guess the IP isn't that far off, maybe two shims. I plan to use a balance 2nd and mainly use it in shallow lakes and rivers. I have two MK 20's paired with G250's and G200B's for most diving. Again, thanks for the replies.

The MK2 is a great first stage. Simple, reliable, and easy to service in the field in a pinch.

Scubapro also markets an O2 service kit that for the MK2 that makes it an O2 compatible first stage - and I use mine on my oxygen deco cylinder.

Safe diving!

 

[axxel57]

You seem to misunderstand how shims work - they only raise the IP - not lower it. The mfg makes a variety of shims available to adjust the IP from the base value resulting from spring tension. If the IP can't be properly adjusted with shims - we'd replace the spring. Factory spec for a Scubapro first stages is 145 - not 143 - or 147.

I'd charge for any parts and time. Assuming you're running a business or value your time - perhaps you charge for your time and materials too. If you don't charge - let me know - I'll send you some work.

Your suggestions that the IP be dropped to make the regs more reliable for use in cold water is not recommended by the manufacturer. Nor would they suggest detuning the second stage. Their trainer compared that to trying to run with a sock in your mouth. Not saying that doesn't work for you, but if someone was diving in cold fresh water - I'd caution him that a non-environmentally sealed piston reg would be more likely to freeflow - particularly if they had poor technique or air consumption. I've seen students free flow in 38 - 42 degree water in MK25's - but never in MK17's. The MK2 EVO's have features to make them more tolerant to cold water - but I prefer diaphragms regs.

You are correct - I have attended the manufacturer's training. For the money ($200) it was a two day course well spent.

You're kind of an odd duck... But please don't take offense! You seem to know more about the Regs than the manufacturer. Perhaps you'll tell us more?

Damn, and I was sure that, if I have a MK2 with 147PSI on my workbench, I could lower the IP by taking off one shim or two ……..

And strange enough, hardly any MK2 coming out of the box has crisp 145PSI.

But maybe SP wants us to first adjust the MK2s to crisp 145PSI at 3000PSI tank pressure before we give them to our customers.

Also strange that I don’t find any Mk2 manual which refers to the crisp 145PSI.

All the manuals I own only state that the IP should be between 125 – 145PSI in the tank pressure range of 300 – 3000 PSI.

One states (Wolfinger)

‘Never exceed 160psig IP’.



To my experience translates an IP drop of 3-6psi into an increasing cracking effort of 0,1inch/h2o when the 2nd stage is unbalanced and a 5-8psi drop of IP does the same when the 2nd stage is balanced.

So if a SP tech teacher insists on a crisp 145psi adjustment instead of a range, then I would like to hear how he would defend this concerning the performance of the 2nd stage.

Obviously I don’t know more than the engineers, who designed the MK2, but I guess I know more and have more experience than most of the SP technicians (okay, that’s not difficult, there are many) and the people who conducted the Repair Courses of the various brands I attended, among them SP.

I’m sure there are better courses and teachers than I got to know, but I’m happy that I never had to pay for those certifications. Probably I would have to attend courses in the US or Europe to find more competent technical staff of the manufacturers.

And sometimes it really crosses my mind that I might know more than the manufacturers of SP about what one should be able to expect from a diaphragm 1ststage, when I see how substandard to my opinion their diaphragm 1sts seem to be (yes, I know that is why I don’t have many friends here around).

I wouldn’t dare to bring some like those on the market.

But then, it’s not completely true. SP tells their techs very honest to expect a IP difference of 2-12psi between full and near empty tank, because they probably know they will get away with that with their customers.

I’m still waiting for the first MK17/11 with a less than 5psi difference and the highest I found was 15psi (like a new MK2).

The two MK11 and the MK17 I was working on this morning had a difference of 8 each and 10psi.

So I guess you misunderstood something with your crisp 145psi or your course director was one of those specialists I also got to know, in this case one who knows more than the SP manuals.

To me your crisp 145psi rule simply doesn’t make sense, but who knows maybe you can convince me with some good arguments.

 

[Wayward Son]

more notes taken...

 

[redacted]

Setting IP at 145 makes perfect sense if you are in the business of servicing regs and don't mind scamming customers. IP tends to icrease over time so setting it at the top of the spec range should bring the rig back for another service sooner. Perhaps this is what is taught!!!

I try to set IP on the low side of the range and expect to go 5 years between service.

 

[bl6394]

Fellas

... crisp 145PSI... <TL-DR/>

Sounds like you don't like the word "crisp." Language can be a barrier. You may have seen an IP that "locks-up" in a reasonably short period of time without subsequent creep or droop - this would be a "crisp lockup." You also don't seem to like an IP of 145psi either. Meh - that is the standard for Scubapro first stages at 3000 psi supply pressure. Communicated by the Scubapro technical manager, Rene Dupree, during training, reinforced by the service manuals and reference video's.

Hope that helps.

 

[bl6394]

Setting IP at 145 makes perfect sense if you are in the business of servicing regs and don't mind scamming customers. IP tends to icrease over time so setting it at the top of the spec range should bring the rig back for another service sooner. Perhaps this is what is taught!!!

I try to set IP on the low side of the range and expect to go 5 years between service.

With respect awap, I'm largely in the business of developing Enterprise software for a credit card processor. Perhaps 4% of my income comes from teaching scuba, and to a much smaller degree other scuba related activities (blending, reg repair, etc.). Asserting that "an IP of 145 makes perfect sense if ... scamming customers" is purely an opinion or yours - and not one I'd bother to debate. If your implication was that I'm in business to scam customers.- that's simply ridiculous.

But I thought your later statement was interesting. "IP tends to increase over time" Let's give this some thought - as it tends to relate to a DIY forum on this board. We probably agree that the IP isn't increasing because of the spring's metal fatigue. That would actually cause a decrease in the IP. So why are your IP's increasing. Would you agree that the seat is becoming more worn and requiring greater force from the piston (assuming a MK2) to lockup? I wonder if perhaps a service interval of 5 years contributes to a worn HP seat? Have you considered that your service interval far exceeds Scubapro's recommended service interval of once every 2 years - or every 100 hours of use?

More importantly - let's imagine for a second that you, Awap, were in business. Something goes wrong and you're in court defending your actions against a civil suit. Which would be the more credible position?

• I am currently a mfg Trained Technician - and I serviced the regulator in a manner compliant with the manufacture's guidelines published in factory training courses, service manuals and reference video's
• I just kind of do what I think is right - because in my experience as Awap - that is the right thing to do? And someone on the internet named axxel57 thinks so too!

In the former case - we'll leave it to a jury. In the latter case - you're loosing your shirt

Cheers, mate!