Mk17 vs Mk17 EVO

[halocline]

Thems alot of fancy words man...

1. IP increases as tank pressure drops on all balanced Scubapros. The Mk2 decreases with drop in tank pressure.

2. You tune all Scubapro seconds at 500psi because that is where IP is highest. Obviously on Mk2 this isnt the case but I've never seen a difference provided the Mk2 was within spec.

3. Everything could be better from an engineering and technical standpoint. How much do you want to pay for a first stage. Scubapro doesnt market or tell us to market IP inversion as some kind of feature to sell regs. They educate us as techs so that we know whats happening with a reg and can ensure that it's within spec.

Wow, are you really a SP tech? If so, it might be time to re-take that rigorous one day seminar.

1. IP does not increase as tank pressure drops on ANY balanced scubapro 1st stage other than the MK11/17. Here is a list of SP balanced 1st stages in which IP does not increase throughout the supply range: MK5, MK7, MK10, MK14, MK15, MK20, MK21, MK25. I might have forgotten a few.

2. There are two whoppers in this one; first, its only the MK11/17 where you need to tune the 2nd at low tank pressure. All others should be tuned at high tank pressure, although with a balanced 1st and 2nd it doesn't make too much difference. Second, with the MK2 it's far more important to tune the 2nd stage at full tank pressure, because the MK2 has a much larger IP swing than any other SP 1st stage, and it's usually paired with an unbalanced 2nd stage. Saying that "you've never seen a difference" in the MK2 between high and low IP is pretty scary, especially for such an educated tech.

3. This whole thread went sideways because Scubabros claimed precisely that SP does market the IP inversion as a deliberate performance enhancement, which it absolutely is not. Several people debunked his claim, apparently you are doing so as well.

To many of us DIYers, when someone comes on this forum and announces that he is a certified tech, then proceeds to make clearly false statements that demonstrate a basic lack of understanding about regulators, it's a great affirmation of why we do it ourselves. Thank you for that!

 

[Scuba Tiger]

Negative.

I would be in agreement that it's an intended performance enhancement. I thought it was pretty clear that I felt like a fixed IP wasnt realistic and thus it would be better to have performance improve via rising IP as tank pressure decreases. I would classify the IP inversion as consistent performance in the sense that performance is maintained or improved throughout the dive as opposed to something like a mk2 where performance technically degrades.

 

[Scuba Tiger]

I know its hard to believe right?

Not sure where he stated it's marketed as a benefit, but I already said it was not. Do I think it's a benefit ya. Is it a big deal. No.

I read his post as trying to be helpful.

You're welcome!

 

[Scuba Tiger]

 

[axxel57]

Correct, for the MK25 you have to expect an inverted IP of about 2- 5psi, so the IP should be adjusted at 500psi.

Can you show the piston 1st IP inverton also for the MK21?

 

[Scuba Tiger]

The results are similar

 

[eelnoraa]

I have two Mk25AF and 1 Mk20. They behave different strictly speaking. Mk25AF IP increase ever so slightly from 3500 vs 500psi. I think 2-5PSI is reasonable guess. It is within 1 click in my IP gauge. But my Mk20 actually drop IP from 3500 vs 500. It is also small, within 1 click, but goes in a different direction. At first I thought they are just random unit to unit variation. They do have different piston inside. Can this be the reason for IP to swing in opposite way?

I also measured 3 atomic and a Legend. All IP don't change more than 1 click in my IP gauge either. To me, they are very constant. A 12 PSI change will be more than 2 clicks, should be very noticeable.

 

[axxel57]

The results are similar

Inverted or not?

 

[Scuba Tiger]

Yeppers. Just like the Mk25.

 

[buddhasummer]

Would be interesting if your SP Guru would dare to claim that they could have designed their Diaphragm 1sts in a way that the higher IP would be produced with fiull tank like with pistons 1sts and the lower at low tank pressure.

That would be finally something really innovative from SP.............

All Diaphragms 1sts I know and which have been on the market for decades have the lower IP at full tank which is technically logical, and have a higher IP at near empty tank, as all piston 1sts I know have the higher IP at full tank and the lower at near empty tank.

Man, use your brain.......

I thought so too until I serviced three SEA/Supra/Cousteaus where the ip drops at low tank pressure by around 4-6 psi. I was surprised. Live and learn.