Scubapro Balanced Adjustable 156/109 with MK 18 2nd stage, a good idea ?

[scubafanatic]

I have several sets of both, the Conshelf is easier to work on, less finicky on adjustment, easier to get parts for, flows more air and exhaust more easily due to the 30mm exhaust valve vs 25 for the 109. The Conshelf has a lower WOB and is equally rugged and simpler. The Titan XL is a plastic Conshelf and it too will kick 109 butt.

If I recall, the 109 (and the G250) got a 3 out of 5 on the ANSTI test at 75 RMV at 135 feet and the Titan XL a 5. The Conshelf is probably a 5 or at least a 4.5.

The 109 is prettier though, I give it that. Your 109s will do fine with the Mk 18 or as a friend of mine, with a Titan or Conshelf first. Mine have Mk Vs or clone Mk Vs. I prefer the clones.

N

I'd considered mating the 109/156 2nd stage to one of my Titan 1st's, but thought that might complicate servicing with a 'Franken-reg'. Now I'm getting mixed reviews on the IP stability of the MK 18, even with an upgrade to the Mk 11/17 poppet one poster says it's still unstable ?

---------- Post added December 8th, 2013 at 01:49 PM ----------

The MK18 is not a sealed diaphragm. It's a MK16 with a turret, not a MK17 with one. They are typically rebuilt with the newer MK11/17 poppet and function pretty much the same. I think it's a fine first stage and I don't think you'll have any sort of problem with it at all.

Other than the MK10+, all the MK10s are functionally the same, although as Fishpie pointed out there were some cosmetic differences. Even though the later SPEC models had the groove (good luck finding a boot for those!) you could still seal the earlier ones, it just might be a little messy. I've had excellent luck sealing my late model MK5s with the small ambient chamber holes, and overall I like MK5s better than MK10s. But that's more personal preference than any actual performance issue.

Here's an interesting point; neither the MK10 nor the MK18 will provide completely stable IP across the supply range. MK10s will drop a good 7-10 PSI from 3000 to 500 tank pressure, and MK18s will rise about the same amount. If your 109 has been refitted with a balanced poppet, you won't notice any difference. If you want really stable IP within a few PSI over the whole supply range, the MK15 or 20/25 is your ticket. I am a big fan of the MK15, but it has some disadvantages, namely a unique seat that's harder to find and it requires a specialized set of snap ring pilers to service. But it lasts a long time; I service mine on 5 year intervals at most.

If your 109 has been serviced expertly, which includes careful examination and possible replacement of the lever, all rubber parts, and the chrome is in excellent shape, I don't think $145 is unreasonable at all. It's kind of scary though to think they're that pricey these days; I don't think I've ever paid more than $30 for one. But that doesn't include the new parts.

Enjoy your new regulator, and I suspect if you get the right mouthpiece and hose set up for the upgraded/restored 109, you won't want to just use it as back up.

I felt the $ 145 was fair, given the condition per the photos, and all the claimed new parts, so I'm glad I apparently didn't get ripped off there. I'm concerned about the IP creep issues though, so if you had to recommend the best SP 1st stage from an IP stability perspective, what would you suggest ? How do you feel about the MK 17 ?

---------- Post added December 8th, 2013 at 02:00 PM ----------

scubafanatic

As you probably know, the 109 has a big fan group in this forum,and whatever problem you might face with it in the future, you will find excellent advice here.

Concerning the Mk18, you might have to decide sooner or later (if it has not be done yet) to replace the old poppet - seat configuration with the newer one(MK11 - MK17).

If you should find in your MK18 the old configuration, you probably can find that out by just connecting your 1st to an IP meter. The old MK18 is a notorious creeper, if there is the slightest imperfection on the hard or soft seat,the IP will creep quite a lot.

If the imperfection is bigger it will override the 2nds.

I've been servicing a MK18 - D400 of a professional videographer now four times.

Since the service intervals were relatively short, and in between I had to change - clean the poppet - soft seat components, I suggested to change for the newer Mk11 -MK17 configuration what he agreed. With the newer configuration there is hardly any noticeable creep. So far so good.

That was in March, he has been working almost very day with it and last week I did a service again.

What I realized in the process of changing and testing was that with the old configuration there was the problem with the creep, but the balancing was excellent,just 2 - 3 psi difference between full and near empty tank.

With the new configuration the IP was solid,but the balancing even lousier than the one of the MK11 - MK17.

The difference between full and near empty tank is now 13-14 psi.

When I told the guy that, he decided to stay with the new configuration, because he did not expect much effect he might be able to feel while diving because of his very good 2nd stage, which I agreed.

So if your 109 should be still unbalanced and your MK18 has still the old poppet - seat configuration,you might want to hang on with it for a while until you got your 109 balanced, because an IP change of 13 -14 psi with the newer configuration (if it should be in the same range in your 1st stage), could easily translate in an increased cracking effort of about 0,3 inch/h2o.
That is a difference you probably will feel while diving.

In this case you would have a harder breathing regulator in the beginning of the dive, which breathes better and better towards the end of the dive.

If your 109 is already the balanced version, then you might look for a change for the new configuration for the reasons mentioned above.

Anyway, good luck with your new 'Baby'.

I appreciate the insight, and now wonder if I should shop for a MK 17 ? ...but then I also saw "the balancing even lousier than the one of the MK11 - MK17." ...which sounds like no matter what I do (upgrade MK 18 to MK11/17 poppet/seat or just buy a MK 11 or MK 17) I'd still be screwed when it comes to IP stability ?

Now I'm leaning more towards just building a Frankin-reg: 109/156 1st with old-trusty Aqualing Titan 2nd, which is OK with me other than complicating servicing. Scubatoys now supports Scubapro (but not Aqualung) but I think they could still service both brands......guess I'll need to give them a call to confirm that.

 

[reefrat]

"Now I'm leaning more towards just building a Frankin-reg: 109/156 1st with old-trusty Aqualing Titan 2nd, which is OK with me other than complicating servicing."

My "Frankenreg" is a Conshelf IV Supreme first stage (circa 1975) with an upgraded older Mares Abyss first- works great!

 

[halocline]

Now I'm getting mixed reviews on the IP stability of the MK 18, even with an upgrade to the Mk 11/17 poppet one poster says it's still unstable ?

I'm concerned about the IP creep issues though, so if you had to recommend the best SP 1st stage from an IP stability perspective, what would you suggest ? How do you feel about the MK 17 ?

which sounds like no matter what I do (upgrade MK 18 to MK11/17 poppet/seat or just buy a MK 11 or MK 17) I'd still be screwed when it comes to IP stability ?

IP stability is not the issue; nor is IP creep. Both of those issues are due to inconsistent lock up or poor sealing at the HP seat. Assuming your MK18 has been upgraded to the MK17 poppet, which is likely because I think dealers were doing it automatically at annual service, it should lock up very quickly and consistently. The issue is that IP rises throughout the supply range, sort-of like an unbalanced diaphragm reg of old times. Since you're using a balanced 2nd stage, it will compensate for the change in IP and you probably won't even notice it. I never realized the IP rose on my MK11 until someone (probably axxel) pointed it out and I tested it.

The MK10 is a balanced piston reg, but still the IP drops through the supply range. This is mostly due to friction at the HP o-ring, I believe, although part of the reason is because there is some surface area on the piston edge, and as such, some downstream force from HP air.

So what this means is that as long as the first stage is in good working condition, IP will lock up quickly and reliably, but it will gradually change as the tank empties. With a balanced 2nd stage you won't even notice.

OTOH, the titan/conshelf 1st stage is universally respected and the design has a decades-long track record, so there's nothing at all wrong with using one of those with your 109. The 109 doesn't need any actual SP parts for service once the poppet has been upgraded. It's just o-rings and a seat that the trident catalog has, although those balance chamber o-rings are tiny and a little hard to find. Point is, I wouldn't be too concerned about servicing.

 

[Fishpie]

What AXXEL57 has discovered is that the 11 and 17 have a wide difference in IP from full tank to empty tank......this is different from creep.
In other words the 11/17 is not particularly well balanced but the IP does lock up well.

You have a balanced 2nd stage, you would be hard pressed to tell the difference in breathing with a 1st stage that starts off at 125psi IP at the beginning of a dive and finishes at 140psi.

I suspect there would be very little real world breathing difference between using your Conshelf or MK18 with your Balanced Adjustable.

 

[axxel57]

scubafanatic

Halo (and now Fishpie) were faster and right again. If your MK18 configuration is already changed for the newer, the IP stability won't be an issue.

And this is the by far more important point, this is why Sp was taking care of it quite a while ago.

That the newer configuration is so substandard concerning the balancing, is to my opinion embarrassing for SP,but it can hardly produce any dangerous situations.

As mentioned before, if you use a balanced 2nd stage with it, you quite probably could not feel any difference to a well balanced 1st stage.

If you should combine it with an unbalanced 2nd, depending on the extend of the bad balancing (for whatever reason the results of the new configuration are quite different from one 1st stage to another),you might feel it.

Your Frankinreg sounds to me as a reasonable alternative, I would not hesitate to combine and dive it.

Most important, enjoy your 109 with whatever 1st stage.

 

[scubafanatic]

I just want to thank everyone that's chimed in so far, a lot of good input and insight. Odds are I'll try the Frankin-reg concept first and see how it goes. Thanks again ! Karl

 

[ams511]

I just want to thank everyone that's chimed in so far, a lot of good input and insight. Odds are I'll try the Frankin-reg concept first and see how it goes. Thanks again ! Karl

Give it a go and see how it works. Also if you decide you want Scubapro, before going to eBay you should check here if someone has something to sell. Some members sell serviced gear very reasonably.

 

[AfterDark]

My 1st 109 is starting its 44th year of diving this January when I do the New Years day dive. I have two more bought from Ebay that are like new. Two are on the old Mk V 1st stage the other is on a MK 10 1st stage. I wouldn't take new regulators in exchange for these. I'm not to cool with these modern day plastic toy regulators. Give me chromed brass any day!

You'll be happy with that choice for years to come.

 

[scubafanatic]

Give it a go and see how it works. Also if you decide you want Scubapro, before going to eBay you should check here if someone has something to sell. Some members sell serviced gear very reasonably.

I've bought a few things from SB members with good results, but do most of my shopping via WWW sites like E-Bay as it's so much easier to see photos already posted of items. I did have some VERY good luck last week (E-Bay), and again this past weekend (not E-Bay though), and acquired 4 essentially MINT condition SP 109/156 BA 2nd stages, fully rebuilt witn new 'old stock' parts and a long list of upgrades, alomg with a very good condition 'regular' 109 'adjustable' that has been rebuilt and upgraded internally (just not upgraded to 'balanced'). Once they all arrive I may post a few photos, if anyone's interested.