MK2 overhaul question

[Wayward Son]

you just addressed the question that came to mind from awap's post.

If shims are used to increase IP by adding pressure to a spring, then what makes the IP increase over time between servicings? I would think that if the spring weakens that would lower the IP. No?

I'm not asserting anything as fact, I'm new to this & learning before I start taking anything apart and I have a Mk2+ that's one of the stages to do at some point.

 

[redacted]

Wow.

So now the idea of where within the specification range the IP is set becomes a matter oh legal liability. That tech course must cover some critical topics.

I am not accusing you of intentionally scamming your customers. I accept your claim that you were taught that. Scuba manufacturer service recommendations and policies have long been based on shop profit rather than equipment performance.

A new scuba seat starts wearing as soon as it is used (somewhat like a car tire). As long as performance stays within spec, it should be OK.





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[bl6394]

you just addressed the question that came to mind from awap's post.

If shims are used to increase IP by adding pressure to a spring, then what makes the IP increase over time between servicings? I would think that if the spring weakens that would lower the IP. No?

I'm not asserting anything as fact, I'm new to this & learning before I start taking anything apart and I have a Mk2+ that's one of the stages to do at some point.

Yes. As the spring weakens (through elastic fatigue or creep) the force it produces on the piston will decrease causing the regulator to lock up at a lower IP. Adding shims will pre-compress the spring - and bring the stiffness back to it's factory value. My assertion that worn a worn IP seat is causing Awap's IP to increase over time is just conjecture. It could also be some damage to the knife edge of the body. Either case will require a greater than standard IP to shut off the flow of gas - and fix the IP. My best guess.

I suspect that if it was just worn orings - and HP gas was going around the seat somehow - the reg would have an IP creep - until the second stage burped the excess pressure - and then the whole cycle would repeat.

 

[bl6394]

Wow.

So now the idea of where within the specification range the IP is set becomes a matter oh legal liability. That tech course must cover some critical topics.
.

You're correct. Liability was one of the topics taught. But liability is part of every scuba professional training program you'll find - from Divemaster through Tech Instructor. Blender to Regulator Repair Tech.

Not saying it's right. It is what it is.

 

[NotSure]

I believe that when a spring weakens it is called plastic deformation. Elastic deformation is the normal compression of the spring that is reversible.

 

[bl6394]

I believe that when a spring weakens it is called plastic deformation. Elastic deformation is the normal compression of the spring that is reversible.

Thank you! I googled for a bit to see if I could find a description about how compression springs fatigued over time, how the stiffness would change based upon cycling etc - but I couldn't find a clear description of that behavior in the time I spent searching.

 

[rhwestfall]

actually, I believe you are both were wrong (not completely, but, since we are splitting hairs here)... both the terms you used (plastic and elastic) are for tensile stress mechanics

for a spring, it would be compressive - fatigue failure, work hardening, etc..... now correctly eluded to in the post above..

link: https://en.wikipedia.org/wiki/Deformation_(engineering)

 

[redacted]

You're correct. Liability was one of the topics taught. But liability is part of every scuba professional training program you'll find - from Divemaster through Tech Instructor. Blender to Regulator Repair Tech.

Not saying it's right. It is what it is.

Unfortunately, regulator sservice errors seem to occur fairly frequently. Perhaps you can identify the specific cases you examined during your course.

 

[axxel57]

Fellas


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.

I know my English is not very good, but up to now I had the feeling that my arguments are basically understood.


I have neither a problem with the word crisp nor with adjusting the MK2s IP to 145psi at full tank.

Actually I always try to adjust the IP to 145psi, because that helps to keep the cracking effort of a well adjusted unbalanced 2nd in conjunction(?) with an unbalanced 1st low also at low tank pressure, and of course to scam my customers into an earlier next service ( okay so, awap?).

But if I reach only 143psi in the first try, I would not feel especially professional if I fiddle around with different shims to reach crisp (exact) 145psi, given the fact that I understand that that difference technically doesn’t have any significance.

Point is, with all due respect and bad English, you seem to be one of those bright eyed relatively new Tech Pros who believe that everything said by the chief technician of SP or other teachers in those two day courses is right and law, even when with your technical background and the ‘Regulator Savvy’ you should be able to understand that differences we are talking about are so small that a

‘Intermediate pressure should be

125psi – 145psi at 3000psi and 300psi

supply pressure.’

from one of the manuals is more appropriate than a ‘Factory spec for a Scubapro first stages is 145 - not 143 - or 147!’

Your insisting on the 145psi spec together with your liability argument in context with our discussion here gives the impression it would be certainly a good idea for you to hang around here in this forum and learn to differentiate instead of just repeating what supposed specialists are saying, even if it doesn’t make sense technically and has not been published in any repair manual (at least not in the four different MK2 manuals I own).

It is an ‘absolute’ position like yours among others which have led to a pretty questionable reputation of Tech Pros here in this forum to say it friendly.

Don’t worry about awap, he likes to provoke.

For him are the vast majority of Scuba Tech Pros ‘scammers’ (maybe Herman would find mercy in his eyes),he must have been badly traumatized when he was young.

Don’t believe him that he would adjust a MK2 on the low side of the range as he does with his balanced MK5 and MK10s to save money, at least not if he would plan to dive the currents of Cancun or the Maledives.

He knows too good what that might mean; I don’t believe he would take chances……

You seem to be in a way kind of typical duck….But please don’t take offense!

Just joking........

For me the increasing IP of a 1st stage simply happens by a worn soft seat, the creep is simply longer before lock up.

Shims in the Mk2 get thinner with time and use.

My experience with the MK2 main spring is that it weakens with time and use while for example the spring in the R-series is stiffening with time and has to be changed sometimes because it becomes almost impossible to adjust them for example to 1,0 inch/h2o cracking effort.

I have no idea why some type of springs are weakening with time and use and others seem to stiffen.

Where are you guys going now with this liability issue?


Cheers

 

[redacted]

I do keep my flowby piston on the low side too.. While a small difference, it does lower the forces that wear the seat. The only exception is if I were to use an older 108 where tuning is done by adjusting IP.