A little advice on 2nd stages please

[analbeard]

I've recently come into possession of two brand new US Divers Conshelf XIV 2nd stages (same as below)

They're both chromed and in mint condition. I'm of a mind to sell one and keep the other as a spare, but i've no idea how much they're worth? Can anyone help me out here?

Secondly, is it worth hanging onto one? I know they're an old design but they're also supposed to be pretty bulletproof.

 

[USdiver1]

You have just acquired the last two regulators that you will ever need. Connie XIVs are one of the benchmark regulators, meaning one of the best regulators ever made. They are still used extensively by military and commercial divers, and many of Aqualung's recent regulators Titan, Mistral are internally Conshelf XIVs in their first stage configuration. Keep em both, use one as your primary, go-to regulator, and keep the other for future use, for when you wear out the first (don't worry can't be done).

 

[Diver0001]

How old are they?

You can usually tell on the older aqualung 2nd stages how old they are by the serial number. The first 2 digits of the serial number are the year of manufacture. For example 76xxxxxx is made in 1976. I don't know when they stopped doing that but for the older ones it will tell you.

The metal ones will be more interesting for collectors than the plastic ones. Depending on age and if they're in good shape and how well/poorly the restoration work was done then you'll be able to get a minimum of about 30 pounds for it. If you get an avid collector interested and it really is in mint condition you might get 100 but I wouldn't expect more.

R..

p.s. as for reliability. I have one that was made in 1972 and it works as well today as the day it rolled out of the factory. The down side of the older down-stream 2nd stages is that they get stiff (a little harder to breathe from) as you go deeper. They had a large diaphragm in order to compensate for the relatively stiff valve mechanism and while the valve mechanism is very similar to the ones still used in modern regs, a lot of development has gone into making 2nd stages breathe easier at depth. So compared to a modern reg I would say equally reliable but higher work-of-breathing. I would recommend taking it with you on a deep dive to try it out so you can experience what i"m trying to say.

R..

 

[halocline]

The down side of the older down-stream 2nd stages is that they get stiff (a little harder to breathe from) as you go deeper.

R..

Can you explain this assertion?

 

[DA Aquamaster]

I'm all ears as well.

The IP is constant relative to ambient pressure, so the valve in the second stage won't know the difference. It's true that air as a breathing gas becomes more viscous at depth due to the increased pressure and density, but that does not effect the regulator until you are around 600' deep, and even if that were in the recreational ballpark, you'd be on trimix long before then and helium slips throughs regs much easier anyway, so the flow increases by about 20%.

Now, it's also true that companies like Apeks (a subsidiary of Aqualung) have marketed an "overbalanced" sealed first stage design that increases the IP at depth, however that's due to a flaw in the sealed ambient chamber design where the area of the outer diaphragm is greater than the area of the inner diaphragm, resulting in greater assist in opening the first stage valve at depth, increasing the IP at depth. That greater IP in turn means greater assist to open the second stage valve, but that requires one of two things to eliminate free flows at depth:

1) detuning the first stage so it breathes harder at shallow depths, or
2) reducing the downstream bias of the second stage so that it does not notice the increased IP as much.

The first "fix" has an obvious downside for most divers who spend most of their time at depths shallower than 100'. The second "fix" is worse, as it greatly increases the pressure needed to vent gas if the first stage seat was to leak. A few years ago there were problems with the little used (during the dive) first stages on back up regulator having seats that creeped/leaked with a resulting increase in IP high enough to cause the shraeder valves in inflators to fail, resulting in an un-commanded inflation at depth.

____
i like the old Conshelf XII and XIV second stages. They breathe far better than they have any right to breathe and they are bullet proof. They'll go about a decade between annual services and then you can flip the seat, so if I was stuck on a deserted island with unlimited air and no reg parts, I'd want a Conshelf XIV.

 

[Diver0001]

Can you explain this assertion?

As far as I can remember they don't have venturi flaps, any kind of manual adjustment and the poppets are not balanced. I also think that the springs must have been a little stiffer because the diaphragms were larger, which I assume is to compensate for the stiffer spring and keep work-of-breathing as low as possible. Moreover I've been down there with such regulators so I have some personal experience to draw upon. They're not *awful* at depth. Don't get me wrong, but they're *relatively* stiffer than modern regs in my experience.

R..

 

[analbeard]

Thanks for the input guys, makes for some interesting reading. I don't really tend to do deep dives so I doubt I'd notice any difference anyway.

As to the condition of them, they're brand new and apart from needing a bit of polishing up, they're the same as the day they were made. Will check the serials when I get home so I can establish how old they are.

 

[Diver0001]

I would advise against any kind of "cleaning them up" if you plan on selling to a collector. Often times cleaning them up can actually reduce their value to collectors. If you plan on diving with them then it doesn't matter, of course.

good luck.

R..

 

[analbeard]

When I say 'cleaning up', you can see how clean they are anyway :

 

[DA Aquamaster]

Sorry...it doesn't look old at all so no collector value what so ever. And they are obviously not something to take in the water as they don't have that "proven, reliable, been there and done that for years" look that you need in life support equipment.

Feel free to send them to me for disposal, and as a consolation I'll send you a couple that look like they they've been dove for years.