Mk17 vs Mk17 EVO

[Couv]

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.

How low of tank pressure? There is a point where tank pressure and IP will be the same with any regulator.

 

[buddhasummer]

How low of tank pressure? There is a point where tank pressure and IP will be the same with any regulator.

Around 500psi IIRC.

 

[buddhasummer]

Got curious re my aging memory, re checked one of my cousteaus and at 500psi the ip drops what looks to be around 7 psi.

 

[Rusty Shackleford]

I am going to ask a stupid question. Why not just make a sealed version of the MK-25?

Would that not solve the problem and keep it solved?

What is SP afraid of? Shop techs screwing-up the re-pack?

 

[halocline]

I am going to ask a stupid question. Why not just make a sealed version of the MK-25?

There is one, it's called atomic

SP got away from the SPEC boot/packed chamber environmental seal of the earlier balanced pistons for who knows what reason. Instead they went to some bushings and coatings on the spring that are supposed to inhibit icing.

 

[BoltSnap]

AquaLung has an "overbalanced" feature in its higher end regulators. It looks like the two largest scuba equipment manufactures in the world are trying to fool us not knowing that there are grand experts here on SB who have discovered the great grand racket and, thank God, and have foiled the conspiracy and saved us all from the evil and stupid manufacturers who are trying very hard to rule the universe.

 

[ams511]

The purpose of the first stage is to maintain a constant intermediate pressure, period.. In theory, the IP should not rise or fall with a balanced first stage. In practice, there is a slight variation depending on tank pressure, but the lower the variation the better. There is no point in overbalancing a regulator so that IP pressure increases with decreasing tank pressure. For example, if an unbalanced second stage is "tuned to the edge" for an IP of 135 and the IP increases to 150 at the end of the dive chances are it will start free-flowing. Not what you want. This may be why Buddha's Aqualungs IP drops slightly at lower tank pressure, because the first stages were designed to be paired with unbalanced second stages. If a balanced second stage is used the increase in IP should be compensated for by the balance chamber so there should be no increase in breathing performance. If the tolerances of the balance chamber are exceeded then it to will start to free-flow. If I am missing something then let me know.

An unbalanced first and second combination where the IP drops with a decrease in tank pressure makes more sense. At least an argument could made that it alerts the diver to low tank pressure by becoming more difficult to breath.

 

[buddhasummer]

It still amuses me somewhat that the humble conshelf has the most stable ip accross tank pressure of any reg I've ever owned. Given that SP package the MK17 Evo with an unbalanced second stage seems strange given its up to 12psi and above "inversion".

 

[buddhasummer]

there is a reason for the G260..... Think about it, the 109/156/g200/g200b/g250/G250graphite/g250v all essentially had the same guts. Now they stop making it in favor of the G260 (all different parts).... again, the writing is on the wall.... then again, the G250 could be brought back again in some marketing strategy.... what could they call it???? The "Vintage" was a hit.....

The G260 orifice to BC all can be used in a G250 or upgraded 109, I'm thankful that the guts/heart are still the same/can be used across our most loved models.

 

[buddhasummer]

To add, even a G260 exhaust valve can be used in a G250 or G250V. So as far as "service/consumables" the G260 maintains ties to the 156/G250/G250V. I really do like the G260, IMO on balance, it's the best current production second stage offered by SP.