Question Skipping 1st stage Maintenance?

[CG43]

I had some issues with the Czech tests, as they for example indicate that the intermediate pressure of a MK17 EVO didn't change. I can't fathom how that could have been the case. Every dry sealed diaphragm first stage I ever had in my hands did experience changes in intermediate pressure when you press onto the environmental diaphragm with your thumb. I see nothing special/different on a MK17 EVO.

Don't forget , pressing the invioronment membrane you simulate an greater deeps , so the
absolute pressure must raise for constant IP .

I have always been amazed that a polymer is used universally by all companies for this part. It is one of the very few parts in a regulator that really has to endure high forces and isn't getting balanced in some way.

As a germann you dont know the Dräger SECOR 200 ?
This is a full brass transmitter and I guess it is good for 2000 N or more .

What I don't like is that , if the IP is 10 bar (const) in 200 m the pressure difference the
IP membran has to take is 30 bar , or thre times that of the surface .
30 bar is a lot , the membrane must be in good condition and claped very well .

No wonder that Mares prefered a piston for that design .
On the other side 10 to 30 bar produce different among of friction . To caculate this it is nessesary to know the friction rate .
I guess the friction is not a serious disadvance .

Coming back to the question skipping 1 stage maintenance ?
With the closed design, I would change the two membranes according to the recommendations when I dive deep. Because the mechanical loads and safety requirements increase.

 

[lowwall]

EN250, which had it's last revision in 2014, is even more restrictive than the 50 meter mentioned above.

The vast majority of divers will carry a regulator that is able to supply gas to two divers at the same time. What we commonly call alternate second stage is referred to in the standards as auxiliary breathing equipment and if a regulator is equipped with one, Annex B of EN250:2014 is applicable.

The vast majority of regulators used are technically only certified up to 30 meters.

The reg will be marked EN250A if it has been certified to meet the EN250 standard for both a primary and secondary second stages being breathed at the same time. As you note, this is measured at 30m instead of 50.

Most reg manufacturers don't bother with EN250A certification. It's expensive and few consumers will know what it means. It's also kind of pointless, the 30m test depth ensures that any first stage that passes EN250 with a reasonable margin will also pass EN250A.

The transmitter test done by the Czechs was interesting and nicely showed why dry sealed diaphragm regulators are a nightmare to engineer. The forces acting upon it are tremendous, especially the forces upon its narrow bottom. I have always been amazed that a polymer is used universally by all companies for this part. It is one of the very few parts in a regulator that really has to endure high forces and isn't getting balanced in some way....

This is simplifying things to a good amount as earlier posts clarified, but it is a good enough ballpark figure. Imagine an human adult balancing on the end of a drinking straw and you got a good idea of the forces involved that the bottom of the transducer is exposed to at 100m of depth. I'm by no means surprised that the transducers fail at a certain depth.

This reminded me of something Mark Ellyat wrote since 20 years ago, following his then record open circuit dive to 313m.

http://www.inspired-training.com/deepdiveregulations.htm

He was not a fan of environmental sealing for really deep dives. He said the older type with oil or alcohol filled environmental chambers were acceptable from a mechanical point of view, but that they were incompatible with high O2 gas mixes. But the ones with plastic transducers really bothered him, especially the overbalanced ones (I think Apeks at the time?). They were guaranteed to freeflow when you got deep enough.

FWIW, he used a stock (unsealed) Mares MR22 on his dive.

The current Mares TBP setup answers his objections since it is not overbalanced and uses metal parts. But, I have to admit that I don't see an advantage for additional environmental sealing in diaphragm regulators in normal environments. The working bits are still sealed away under the primary diaphragm which is well protected from danger. And pressure compensation will still occur even if some sand or silt gets into the ambient section. It would need to be completely packed with debris to have an effect. And that effect would only be turning it into an unbalanced first stage, not stopping it from functioning.

 

[lexvil]

This thread has becom a train wreck of irrelevance

 

[admikar]

OH, MY GOD!!!
STOP THE PRESSES!!!
This must be the first time something like this has happened on Scubaboa......oh, wait, nevermind.

 

[rsingler]

I have to admit that I don't see an advantage for additional environmental sealing in diaphragm regulators in normal environments.

There was one exception. The popular Poseidon 3960 had a unique ring that enclosed the diaphragm, which sealed against a thin groove in the ring.
A reg set with 0.5ml residual salt water in the spring area could in fact leak, as corrosion would begin in the dependent portion of the ring over long storage, and eat away at that groove.
A reg sent in for service just would not stop leaking at the diaphragm, until I replaced that part.

 

[lowwall]

This thread has becom a train wreck of irrelevance

I prefer to think of it as part of the never ending quest for knowledge for its own sake.

 

[Tanks A Lot]

The reg will be marked EN250A if it has been certified to meet the EN250 standard for both a primary and secondary second stages being breathed at the same time. As you note, this is measured at 30m instead of 50.

Most reg manufacturers don't bother with EN250A certification. It's expensive and few consumers will know what it means. It's also kind of pointless, the 30m test depth ensures that any first stage that passes EN250 with a reasonable margin will also pass EN250A.

Yes, it is one of the instances where a standard has certainly not converted into real world value. Pointless is putting it quite nicely.

This reminded me of something Mark Ellyat wrote since 20 years ago, following his then record open circuit dive to 313m.

http://www.inspired-training.com/deepdiveregulations.htm

Thank you for sharing this, that was an interesting read. It reminded me of a few conversations I had with Stephen Burton and sure enough he mentions him at the beginning and the end of the article.
A shame that Stephen died to COVID, he was the most knowledgeable person on these topics I have ever met. His website was/is such a great start for many technicians.

 

[CG43]

Hello lowwall

Thanks for the GL Certificate .
I'm not shure that Harald Pauli (GL man)had signed the paper if had seen the
Silvertr Peknik test results before .
I'm shure the Apex can deliver enought heliox at 200 m because the IP is still over 13 bar .
But the kink in the IP curve shows the limit of a meaningful mechanical load.

 

[CG43]

There was one exception. The popular Poseidon 3960 had a unique ring that enclosed the diaphragm, which sealed against a thin groove in the ring.
A reg set with 0.5ml residual salt water in the spring area could in fact leak, as corrosion would begin in the dependent portion of the ring over long storage, and eat away at that groove.
A reg sent in for service just would not stop leaking at the diaphragm, until I replaced that part.

Does anyone have a drawing of this IP jump start for the first seal of the second 3960 stage ?

 

[Umuntu]

It reminded me of a few conversations I had with Stephen Burton and sure enough he mentions him at the beginning and the end of the article.
A shame that Stephen died to COVID, he was the most knowledgeable person on these topics I have ever met.

I wasn’t aware that Stephen had passed . I spent some time with him in Pattaya. Super knowledgeable about regulators and compressors. And a bit eccentric too. Do you know who maintains his scubaengineer website … it’s still working ?