Deep diving and IP

[Red Sea Shadow]

How do you tune your regulators for deep technical diving (150m+)? Some people say that the IP should be raised to handle the required pressure. For example, to do 170m you have to raise the IP to at least 18 bar (17 + 1 ATM). Is it true?

 

[Charlie99]

You are missing a very important fact. The IP of regulators is referenced to local ambient pressure, so raising the IP is not needed. The regulator does it for you automatically.

So a regulator with an IP of 9 bar at the surface will still have an IP of 9 bar (referenced to local pressure) at 50 meters / 5 bar. So at 50 meters the IP will have automatically increased to 9 + 5 = 14 bar absolute pressure. The 2nd stage will still see a 9 bar difference between the pressure at its inlet and the outside ambient pressure.

 

[DA Aquamaster]

A higher IP will theoretically mean greater maximum flow rate.

For example an IP of 150 psi will flow about 20% more gas than an IP of 125 as the internal air passages are otherwise identical. It's the same idea as turbocharging a car - higher manifold pressure means more mass flow through the engine at an identical RPM.

The problem with that reasoning is that the high quality high performance regs you should be using for deep diving, already have a flow rate well in excess of what you need any way, so unless your reg is marginal, it does not matter.

At really deep depths (below 60-0 feet or so, the increased viscosity of the gas starts to reduce flow rate, but at that depth you would be breathing mostly helium anyway and it slips through regs much easier than air.

 

[Charlie99]

DA Aquamaster -- I don't think that Red Sea Shadow is concerned about increased viscosity at depth, overbalanced regs, etc. It seems he is simply missing the fact that IP is relative to ambient and that even a 9 bar IP will work at 170m/18 bar ambient pressure.

to do 170m you have to raise the IP to at least 18 bar (17 + 1 ATM). Is it true?

Not everybody knows as much about regs as do you.

 

[sphillips3]

As mentioned above the first stage automatically increases the "absolute" IP to match the ambient (gauge pressure stays the same with depth). Some first stage systems claim to be "overbalanced" so that IP is increased slightly with respect to ambient as depth increases. In practical terms the increase is so small as to be meaningless. If you had a huge increase in IP with respect to ambient it would upset the second stage and cause a free flow.

 

[ZzzKing]

At really deep depths (below 60-0 feet or so, the increased viscosity of the gas starts to reduce flow rate, but at that depth you would be breathing mostly helium anyway and it slips through regs much easier than air.

Are you saying that below 60' we should be breathing Trimix or was that a typo?

 

[LavaSurfer]

Are you saying that below 60' we should be breathing Trimix or was that a typo?

That might increase the cost of diving ever so slightly

 

[DA Aquamaster]

Definitely a typo - should read 600 feet.

I am not a fan of 30/30 and in fact I think an END of 100' is a little too conservative in some situations. I'd only promote He use at below 59' if I sold helium for a living.

 

[Red Sea Shadow]

Thanks all