Scubapro upgrade ??'s

[halocline]

I should've mentioned I had everything gone through by LDS before the trip. They replaced on item on one 1st stage and they all checked out. On one dive the crew set up the gear with my wifes MK17 on my BC and so I just dove with it. There's a noticeable difference in hers and mine. Thanks for all the input!!

So, you're saying that there is a noticeable difference between the way your MK25 and her MK17, breathes, each equipped with R190 2nd stages? That should not be the case. Each of those 1st stages should provide the 2nd stage with plenty of air flow at a very stable IP. Something is not adjusted correctly, either in one of the 1st stages or one of the R190s. I suspect there's a problem with the R190 that you experienced the positive breathing pressure on, it very well could be what Awap was talking about. What you're experiencing sounds like excessive venturi assist, and it's not really typical on R190s.

The first thing you could do is bring both regs back to the LDS and have them confirm that the IP is correct and stable on both regs. I'd also tell them to adjust them so that IP is the same, maybe about 130PSI. That's pretty close to the middle of the range. Make sure they leave the IP gauge on the regs for a while. After I rebuild a reg, I leave the IP gauge on for several hours and check it every so often just to make sure there's no creep. That might be a little overkill, but at least give it a few minutes. You should also make them cycle (breathe or light purge) the regs a few times to have a look at the IP drop and rebound during breathing. Unless the tech is really clueless he'll know what you're talking about, and if you can watch, all the better. You just want to make sure that the IP drops about the same amount on each 1st stage during a breath, rebounds immediately, and locks up at IP solidly. The whole purpose of doing these things is to eliminate the possibility of a problem with the 1st stages. You really should not have been able to tell a difference between them while diving.

Once that's established, see if you can get the reg to do what it was doing. Try turning the VIVA to minimum venturi assist and see if that solves it. If the IP on your MK25 was really high and they lower it when you bring it back, they'll have to adjust the 2nd stage or it will breathe poorly.

Upgrading 2nd stages will make the regs breathe more smoothly, but it really sounds like there's a problem here that could be fixed. If you do end up buying 2 high performance 2nds like the G250 or S600, it's not going to be cheap! If it were me I'd almost certainly bag that idea and get a used D400 or older G250. But I'm cheap.

Good luck with it.

 

[browntrout]

Thanks for the insight Matt. I'd been thinking lightly used G250V's. New S600's are out of the question, actually new anything is out of the question.

 

[Daz]

I have the mk 17 with a S555 and G250 V. Love the S555 and never use the 250V. Swapped them back and forth to see which one I liked. S555, the winner.

don O

Funny. I did the same and only dive my G250v. My wife uses the s555 and loves it though.
To each his/her own...

 

[Cyclops_Diver]

G250V's on my doubles, and serviced older G250's from eBay for three singles rigs. Just love them, and relatively cheap to aquire on eBay.

 

[DA Aquamaster]

Thanks for the insight Matt. I'd been thinking lightly used G250V's. New S600's are out of the question, actually new anything is out of the question.

When I switched from Mk 25's to Mk 17's on my doubles I used one of each side by side on several dives and for a few dives I even fed the same second stage from each through a gas block. I could detect absolutely no difference between the breathing performance of either second stage and iut included dives to depths of 150'.

That make sense when you look at the flow rates (both way more than adequate) and IP drop/needle swing (both basically identical) as if the air delivery traits are in the same ballpark, the second stage is not going to know the difference, let alone the user.

Matt is I think correct that something must not be adjusted right on one or more of your stages if you are getting a perceptible difference in breathing betwene the Mk 17 and Mk 25.

-----


If new is not an option, go with used G250's (the original 1980's and 1990's version - not the all plastic G250HP). The original G250 is virtually identical to the current G250V. The differences are a round rather than oval hole in the air barrel and some differneces in the inlet fitting nut and external cosmetics. And since the G250V was introduced, the price of used G250's has become sane again.

 

[Wayward Son]

they're right, your 190 should not do that.

That said, I recently bought a Mk25/G250V. I couldn't be more pleased with how it breathes. George tuned it up & did it right. The G250V is a really nice 2nd stage.

 

[demarest652]

I recently purchased a mk25/s600 i love it. I had a hard time letting go of the cash but im glad i did.

 

[browntrout]

So, you're saying that there is a noticeable difference between the way your MK25 and her MK17, breathes, each equipped with R190 2nd stages? That should not be the case. Each of those 1st stages should provide the 2nd stage with plenty of air flow at a very stable IP. Something is not adjusted correctly, either in one of the 1st stages or one of the R190s. I suspect there's a problem with the R190 that you experienced the positive breathing pressure on, it very well could be what Awap was talking about. What you're experiencing sounds like excessive venturi assist, and it's not really typical on R190s.

The first thing you could do is bring both regs back to the LDS and have them confirm that the IP is correct and stable on both regs. I'd also tell them to adjust them so that IP is the same, maybe about 130PSI. That's pretty close to the middle of the range. Make sure they leave the IP gauge on the regs for a while. After I rebuild a reg, I leave the IP gauge on for several hours and check it every so often just to make sure there's no creep. That might be a little overkill, but at least give it a few minutes. You should also make them cycle (breathe or light purge) the regs a few times to have a look at the IP drop and rebound during breathing. Unless the tech is really clueless he'll know what you're talking about, and if you can watch, all the better. You just want to make sure that the IP drops about the same amount on each 1st stage during a breath, rebounds immediately, and locks up at IP solidly. The whole purpose of doing these things is to eliminate the possibility of a problem with the 1st stages. You really should not have been able to tell a difference between them while diving.

Once that's established, see if you can get the reg to do what it was doing. Try turning the VIVA to minimum venturi assist and see if that solves it. If the IP on your MK25 was really high and they lower it when you bring it back, they'll have to adjust the 2nd stage or it will breathe poorly.

Upgrading 2nd stages will make the regs breathe more smoothly, but it really sounds like there's a problem here that could be fixed. If you do end up buying 2 high performance 2nds like the G250 or S600, it's not going to be cheap! If it were me I'd almost certainly bag that idea and get a used D400 or older G250. But I'm cheap.

Good luck with it.

Both of them are set-up with the 190's as the octo's and the 295's as the second. So it is the 295's that we are experiencing the different breathing with.

 

[halocline]

Okay, the R295 is basically very similar to the R190, except there is no diver adjustable venturi. I've never looked inside one (way too new a model for me) but I assume there is a tech-adjusted venturi assist. Maybe one of them has maximum venturi assist, the other minimum. It's just a guess. Try breathing off the R190s and see if those are acting differently as well.