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Question Skipping 1st stage Maintenance?
- Thread starter Pearlman
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halocline
Contributor
Is this statement supposed to be applicable to all scuba regulators? If so, there might be a little bit of semantics at work. I guess what happens is that with enough depth ambient pressure would exceed tank pressure. At that point the first stage valve would remain open, and I’m guessing that water would force its way into the tank through the 2nd stage, if it too were open.
Remember that IP is the force that closes the valve on the 1st stage. On a piston reg, you have the spring pushing the valve open, assisted by ambient (water) pressure. That open valve allows air to flow into the IP chamber until enough pressure builds up to push the piston closed. But that pressure can only be supplied by the tank, so if ambient (plus the spring force) is greater than what’s in the tank, the 1st stage will remain open.
On a typical diaphragm reg, the geometry is a little different but I think the result is more or less the same. Ambient pressure on the diaphragm (plus the spring) pushes the seat off the orifice (via the pin) and if there’s not enough tank pressure to counter-act that, everything stays open.
So it might be just a little tough to breathe off a 2nd stage! I guess the depth at which this happens depends on how much pressure is in the tank.
But surely your comment must have something to do with a specific sealed regulator, because I think in my scenario we’re talking about thousands of meters, not hundreds.
CG43
Contributor
Hello halocline
In metric units ist's very easy .
Vor exapmble : your tank pressure is 170 bar , your IP is 10 bar over ambient .
Substract 10 bar from the tank pressure = 160bar
One bar equals 10 m water colume , 160 bar equals 1600 m water deephs .
Right , that what you said .
The reason that the IP don't stay constant is that the mechanical stress in the closed design raises with the ambient pressure and if the parts are not strong enought they fail . As far as I know only the Mares and the Poseidon are certfied for 200 m . For 50 m will al do well .
In metric units ist's very easy .
Vor exapmble : your tank pressure is 170 bar , your IP is 10 bar over ambient .
Substract 10 bar from the tank pressure = 160bar
One bar equals 10 m water colume , 160 bar equals 1600 m water deephs .
Right , that what you said .
The reason that the IP don't stay constant is that the mechanical stress in the closed design raises with the ambient pressure and if the parts are not strong enought they fail . As far as I know only the Mares and the Poseidon are certfied for 200 m . For 50 m will al do well .
admikar
Contributor
Also some of Apeks regs (FSR and FST, not sure about DST) are certified to 200 msw.
CG43
Contributor
What I could find was this :
"Apeks pairs the DST first with the XTX50 second as the "XTX50 Regulator" (RG115128) , and the FSR first with the XTX200 second as the "XTX200 Regulator" (RG113122). Apeks markets the TEK3 (based on the DS4) with the XTX50 second as the "TEK3 Regulator Set" (RP112114) packaged as a mirror image pair of regulators. The nomenclature can be confusing, but keep in mind all the Apeks regulator packages are EN250 certified to a depth of {660 fsw | 200 msw}"
But the EN 250 explained as a field of application :
"The purpose of the requirements and tests specified in the standard is to ensure a minimum level of safety for the use of light diving equipment up to a maximum depth of 50 m."
Thats from EN 250 : 1993
I have never heart that EN 250 test go down to 200 m .
And the following tests are from 2019 !
Look what the tests show , are the sealed Apex good for 200 m ?
https://www.rb-forum.cz/data/uploads/2019/prezentace/test-ip-eng-final.pdf
"Apeks pairs the DST first with the XTX50 second as the "XTX50 Regulator" (RG115128) , and the FSR first with the XTX200 second as the "XTX200 Regulator" (RG113122). Apeks markets the TEK3 (based on the DS4) with the XTX50 second as the "TEK3 Regulator Set" (RP112114) packaged as a mirror image pair of regulators. The nomenclature can be confusing, but keep in mind all the Apeks regulator packages are EN250 certified to a depth of {660 fsw | 200 msw}"
But the EN 250 explained as a field of application :
"The purpose of the requirements and tests specified in the standard is to ensure a minimum level of safety for the use of light diving equipment up to a maximum depth of 50 m."
Thats from EN 250 : 1993
I have never heart that EN 250 test go down to 200 m .
And the following tests are from 2019 !
Look what the tests show , are the sealed Apex good for 200 m ?
https://www.rb-forum.cz/data/uploads/2019/prezentace/test-ip-eng-final.pdf
It's a different standard from commercial diving. Quoting myself from another thread on Mares regs:
"The NORSOK U-101 standard has similar requirements to EN250, but there is no set depth. It is up to the manufacturer to select a depth and to provide proof that the regulator meets the standard at that depth which is then stated as part of the certification. All of the Mares EN250A regs also meet NORSOK U-101 requirements at 200m when equipped with the TBP kit. Per the standard this is done with air to 60m and an appropriate Heliox mix for deeper depths. AFAIK, other than Mares, only Poseidon and Apeks are NORSOK certified among recreational scuba regulator manufacturers."
Apeks has this certification for the TEK3, XTX200, and XTX50. Here's a copy of the XTX200 certification.
Tanks A Lot
Contributor
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 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.
I just went into the basement to measure a transducer of an XTX50. The top diameter is roughly 29.5mm while the bottom of the transducer measures around 4.55mm in diameter.
Say you dive to 100m with this, the pressure differential between the ambient pressure at 11bar and dry chamber at 1bar will be 10bar, or 1000000Pa.
The force upon the top of the transducer will be:
FTop Transducer = 1000000Pa x π x (0.01475m)2
FTop Transducer = 683.47N
FTop Transducer ≈ 70kgf
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.
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.
I take their results with a grain of salt, although the core message is correct. An environmentally sealed diaphragm regulator that is sealed with a dry chamber, as opposed to a liquid filled one, is probably the least suitable for extreme depths. The physics are not kind onto the dry chamber.
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 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.
I just went into the basement to measure a transducer of an XTX50. The top diameter is roughly 29.5mm while the bottom of the transducer measures around 4.55mm in diameter.
Say you dive to 100m with this, the pressure differential between the ambient pressure at 11bar and dry chamber at 1bar will be 10bar, or 1000000Pa.
The force upon the top of the transducer will be:
FTop Transducer = 1000000Pa x π x (0.01475m)2
FTop Transducer = 683.47N
FTop Transducer ≈ 70kgf
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.
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.
I take their results with a grain of salt, although the core message is correct. An environmentally sealed diaphragm regulator that is sealed with a dry chamber, as opposed to a liquid filled one, is probably the least suitable for extreme depths. The physics are not kind onto the dry chamber.
Tanks A Lot
Contributor
I want to point out that the often quoted NORSOK U-101 may be a bit of a marketing gimmick.
Tests up to 150m are without any additional heating of the gas. Below 150m the breathing gas has to be heated, which just isn't applicable to SCUBA in any form.
I do not want to discount the usefulness of this standard, but some of it isn't applicable to SCUBA. The heated gas alone makes the physics much easier on the regulator.
Tests up to 150m are without any additional heating of the gas. Below 150m the breathing gas has to be heated, which just isn't applicable to SCUBA in any form.
| Depth (m) | Temperature (°C) |
|---|---|
| 150 | 20±2 |
| 200 | 20±2 |
| 300 | 25±2 |
| 400 | 30±2 |
I do not want to discount the usefulness of this standard, but some of it isn't applicable to SCUBA. The heated gas alone makes the physics much easier on the regulator.
I couldn't see from the summary presentation whether the regulators were being "breathed," i.e. dynamic IP as the regulator is breathed, or just measuring static IP as the ambient pressure increases.
I don't know if that would actually make a practical difference to the results, but if the regulator is not being breathed then neither diaphragm is experiencing any dynamic movement.
Tanks A Lot
Contributor
That is a great point that I didn't even think about - Good catch!
That certainly explains why they might have seen little change in the MK17 EVO. They did not "breathe" the regulator and that is probably why intermediate pressure changed different from what would be expected. Most changes in intermediate pressure occur once the diaphragm is allowed to relax before being pushed outwards again.
The same principle as to why a purge is necessary when fiddling with the adjustment screw upon first setting of intermediate pressure.
Regardless, the no change in intermediate pressure on the MK17 EVO still strikes me as borderline impossible.
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