Why is a Conshelf so reliable long term?

[buddhasummer]

When people ask about bullet proof/bomb proof regs almost exclusively either the conshelf or MK2 are mentioned and not much else except the occasional shout out to some Sherwoods. On SB the conshelf seems have attained legendary status, not saying it's underserved but "perhaps" there are others worthy of equal status.

 

[herman]

For all intents and purposes, the Conshelf and early Titans are identical regs. it's just the exterior shape that is different. In addition, there are several other regs that also qualify, the USD Royal (not Royal Aquamaster) for example. I think the major reason that the Conshelf is mentioned is it's been around the longest and most widely used (including military service) plus the second stage is metal so it also has a longer life span.
Nem, the Royal Master was introduced in 64 but has a different design in the balance chamber than the Conshelf or RAM. Looking at the catalogs, the Conshelf was introduced in 65 and it stated it had the same balancing chamber as the Royal Master so it is possible the first year Conshelfs also had the different balance chamber design of the Royal Master.

 

[Diver0001]

I've read lots about the the long term reliability of the Conshelf first stage and it got me wondering what makes this first stage so reliable? Given the earlier Tiatan is all but the same why does that reg not have the same reputation? For that matter why are no other regs save the MK2 branded with the same reputation. Is the seat material different? Parts used? I thought perhaps it was due to the added relative complexity of newer regs but many regs are similar in their simplicity. Why can a Conshelf go 20 plus years without a service but a titan for example will not, well I've never read any such reports anyway. Cheers.

I think it's the design. I have an aqualung from 1972 that has (what is it?) a couple of o-rings and a seat....... There is nothing to go wrong.

That said, it's not the best performing regulator around. My ancient aqualung will tell you 5 min in advance when the tank pressure is getting low but my modern aqualung will breathe normally until the tank pressure is so low that you can open up the valve and blow air back into the tank. (this is the literal truth!)

My buddy who services 150 regulators a year talks about new regs in terms of bad, worse, worst. In his mind the newer scubapro regs (in his words) have more o-rings than a space shuttle, and he's not the least bit surprised that they are prone to IP creep. He says the same about Mares regs except for the Abyss and he says that cressi regs are "probably made in a toy factory in China". ("Jina" if you are an "orange leaning" American).

I don't know about all that but what I do know is that my modern Apeks/Aqualung regs look factory clean after 3 years of diving (a LOT) with them and only servicing them because of fearing karma.

R..

 

[kelemvor]

When people ask about bullet proof/bomb proof regs almost exclusively either the conshelf or MK2 are mentioned and not much else except the occasional shout out to some Sherwoods. On SB the conshelf seems have attained legendary status, not saying it's undeserved but "perhaps" there are others worthy of equal status.

I suspect it's like anything that has "darling" status on scubaboard. Shearwater dive computers, scubapro jet fins, BP/W bcd's... More bravado than benefit. Not that there's anything wrong with any of these but I bet the reputation is overblown.

I was going to rent some split fins and test my theory once but I was concerned that I would not survive.

Seriously though, how does any regulator avoid things like salt deposits if it's been dove thousands of times without service? I can only guess that the folks pulling this off must take exceptional care at rinse time. I thought I was taking exceptional care of my regs the first year I owned them. The service tech said it looked like I'd never rinsed them after diving. I was at a loss.

 

[halocline]

I suspect it's like anything that has "darling" status on scubaboard. Shearwater dive computers, scubapro jet fins, BP/W bcd's... More bravado than benefit. Not that there's anything wrong with any of these but I bet the reputation is overblown.

That's BS. The reason the conshelf and MK2 (and MK5) have the reputation for reliability is simple; they've been around for decades and have earned this reputation. Other regulators have been built on the same designs and have also performed well, but in terms of longevity and sheer numbers of dives, these old classics have proven themselves. It doesn't mean that some modern regs won't eventually do the same, but that's a question to ask again in a couple of decades.

Regarding the resistance to poor maintenance, the truth is that very simple designs built with robust materials are more likely to tolerate mishandling. In the conshelf, there is one (ONE!) o-ring on the interior of the regulator. On the MK2, there are zero dynamic o-rings that are subjected to high pressure and only 2 dynamic o-rings in the entire regulator. There's just very little that can go wrong.

 

[kelemvor]

Alright, well.. I'm curious and they seem to be cheap. Which model is the good conshelf? All of them? I see XIV, 20, 21, 22, SES, SE2 on ebay. Are they all created equal (or close)?

 

[halocline]

My buddy who services 150 regulators a year talks about new regs in terms of bad, worse, worst. In his mind the newer scubapro regs (in his words) have more o-rings than a space shuttle, and he's not the least bit surprised that they are prone to IP creep.

R..

It is definitely true that the newer SP designs are (IMO) a serious disappointment considering some the past home runs they've hit. Sometimes I wonder if these engineers are just trying to save their own jobs or if it's all about "improving" something to spark repeat sales.

IMO it's especially true with the newer 2nd stages that appear to be built with two priorities: 1) look good in a dive shop sales room, 2) test well on ANSI breathing machines. If they are difficult to self service or require specialized tools, all the better.

The o-ring count would have nothing to do with IP creep. In fact, I think the MK25 current seat/piston is the most stable (in terms of quick reliable lock up) since the MK5. But the MK25 does have a needless external IP adjustment which adds a few o-rings, and there's an o-ring in the piston which is not meant to be serviceable. This means that eventually that piston will leak and need replacement. I have MK5 pistons that probably 35 years old and work perfectly.

"Reliability" can be defined in a couple of ways, I suppose. One way would be to consider how likely a regulator is to perform as intended on a particular dive. Another way would be to consider how likely it is to perform as intended over a very long period of time. Obviously, newer designed regulators have not had the opportunity to prove themselves in the latter way.

 

[buddhasummer]

A screen shot I took so I could reference. Thanks Fishpie.

 

[Insta-Gator]

I've had my Aqualung regs serviced for safety sake. But it's the same rig I trained on in 1989. No problems, no complaints.

 

[iain/hsm]

If you really need to understand scuba regulator design you need IMHO first to look at opposing aspects.

Engineering vs Marketing.
Performance Engineering Design vs Style and fashion, colour and shape.
Engineering Design Mean Time between Servicing vs Acceptable Annual Service for Dealer Profit
Designed Manufacture Inspection and Test Procedure vs Trial and Error on a ANSTI machine
Engineering Tolerance, vs Adequate equipment
Mechanical fits and clearance vs component at the cheapest possible price

But to kick off, the Conshelf unique design features have never been discussed or mentioned, is the engineer behind the project.

Who once paid and gone from the company left a legacy for others to prat about with trying to work out how to improve a product without a clue as to how to start.
Hence the resultant exterior fashion feature changes you see today but inside the same stuff as no one knows how to make an improvement or where to start.

In a nutshell from an engineering perspective its telling someone what you do to make the design without telling how you do it.

Therefore with the same perameter in place the unique mechanical design features of the Conshelf on the 1st stage is (without being too specific) as follows:

1. The method of adhering the HP seat polymer to the metal seat, (seat finish and compound)
2. The unique polymer material itself and shore hardness, flow and set.
3. The “contact area” of the HP seat to body sealing face
4. The radius of the HP seat itself.

By example a military project some time back for a non magnetic divers application for a 1st stage regulator. We designed three different seat profiles each to suit the different demand valve requirements between an open circuit SCUBA set and a closed circuit oxygen set together with an intermediate flow performace mixed gas CCR diluent.

Each aspect of the design application required a different internal design to suit the specific application, for example the flow of oxygen to a diving set being lower than for say an open circuit scuba requirement at depth.

The hysteresis (or sluggishness) in the dynamic response to the demand valve was designed in by using a 0.020, 0.20, and 0.30 mm profile range.
Not much difference in size but critical in performance.

Knowing the difference is one thing, being able to do something about it is key.