Legend ip increase with depth

[buddhasummer]

Can someone please tell me the ip increase per 10 meters of depth or equivalent unit of measurement due to its "overbalancing" Thank you.

 

[stumpy21]

Here you go! The variables can be fine tuned by the Engineers depending on the surface area of the two diaphragms. This would be from the original Legend not necessarily the current one.

MP = MP(surface) + 1.36 X P (depth )


1.36 = surface of external diaphragm / surface of main diaphragm

 

[Umuntu]

Can someone please tell me the ip increase per 10 meters of depth or equivalent unit of measurement due to its "overbalancing" Thank you.

Here you go! The variables can be fine tuned by the Engineers depending on the surface area of the two diaphragms. This would be from the original Legend not necessarily the current one.

MP = MP(surface) + 1.36 X P (depth )


1.36 = surface of external diaphragm / surface of main diaphragm
View attachment 419760View attachment 419761

I think the above answer is too simplistic and overstates the "overbalancing" effect.

• In essence you are looking at the arc formed by the external diaphragm in response to the depth pressure. In particular whether the arc depression of the secondary environmental diaphragm is greater than what the arc of the primary diaphragm would be in the absence of the secondary diaphragm.
• It's useful to analogise the arc of the diaphragm as a trapeze rope, a longer softer rope will arc more than a shorter stiffer rope in response to a force applied to the rope.
  
• Rather than look just at the external size of the diaphragm, you should look at the diameter of the part that can flex. That would be the inside diameter of the clamping holder below each of the primary and secondary diaphragms, and not the size of the diaphragm itself.
• While the depth of the arc will be proportional to the diameter of the working surface of the diaphragm (surface area is derived from diameter, so it's a way of saying the same thing), it will not be a simple arithmetic ratio.
• The elasticity of the external diaphragm and primary diaphragm will be a factor. Most external diaphragms appear to be made of a much softer silicone material than the fabric reinforced primary diaphragm. So I would expect the secondary to flex more than the primary would in response to a given pressure.
• It's only the deepest part of that arc that matters, since that is what transmits the pressure.

It's hard to guesstimate the exact increase without simulating it in a pressure pot with similarly tuned sealed and unsealed regulators, especially with the difference in elasticity of the two diaphragms. However, I think the above formula would exaggerate the overbalancing effect. For the math describing the effect of pressure on a thin circular membrane see below. It's not such a trivial math topic.

http://www.springer.com/cda/content...194887-c1.pdf?SGWID=0-0-45-1144739-p174105164

 

[Umuntu]

EDIT

@buddhasummer The page below by Mark Ellyat (with input from Stephen Burton of http://www.scubaengineer.com/) has a discussion on the effect of over-balancing environmentally sealed diaphragm regs. If you scroll down there is a table illustrating the effect. The effect is trivial at recreational depths, but more serious for very deep dives.

deep diving regulators

I don't know whether Apeks have moderated their overbalancing, as the XTX50, TEK 3, and XTX200 regulators have EN 250 certification to 200 metres

 

[cerich]

The environment piston/transmitter design is also critical..

 

[buddhasummer]

Thank you for taking the time to reply. I appreciate it. I'll read up on the subject.

 

[northernone]

I appreciate the in depth reply. Thank you for explaining, I've not found this information elsewhere and found it helpful.

Regards
Cameron