Out of air incident.

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Dan

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Dan, I learned to dive by building a hookah. I had no money but I salvaged a 2 stroke lawn mower engine, found 2 very used second stages for cheap at a scuba shop, and splurged on a brand new oil-less compressor and 2 harnesses with one way valves to mount the regs. Built the floats out of big PVC and used them for air storage. Yeah, the air smelled like glue for awhile. It put out about 50 psi. I had two 25 foot air hoses and sometimes I connected them together and went down until the hoses wouldn't let me go anymore. At that point I had to breathe slow and steady, but I could breathe.

Hook up your reg, turn the tank on and off and breath while you watch the spg. You can breathe it to zero. At 60 feet you could only breathe it to 26 psi.

Now you are comparing apple with orange. 50' line would give 7 x more volume than 90" line plus your big PVC air storage at 50 psi.
 

BRT

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Now you are comparing apple with orange. 50' line would give 7 x more volume than 90" line plus your big PVC air storage at 50 psi.

Why don't you forget trying to think it through and attach your reg to a tank?
 

Dan

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Why don't you forget trying to think it through and attach your reg to a tank?

I'm not diving with hookah. I'm using the regular AL80 3000psi tank strapped on my back. When the tank pressure down to 150 psi, that's the minimum pressure drop that my Scubapro MK25 need to deliver intermediate pressure to my S600 2nd stage regulator. Basically the MK25 regulates the tank pressure from 3000 psi to 150 psi before going to the low pressure hose and to the 2nd stage regulator.

Your compressor can only put up 50psi, so you don't need the 1st stage regulator, you just need the 2nd stage regulator that you use to breathe on.
 

BRT

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I'm not diving with hookah. I'm using the regular AL80 3000psi tank strapped on my back. When the tank pressure down to 150 psi, that's the minimum pressure drop that my Scubapro MK25 need to deliver intermediate pressure to my S600 2nd stage regulator. Basically the MK25 regulates the tank pressure from 3000 psi to 150 psi before going to the low pressure hose and to the 2nd stage regulator.

Your compressor can only put up 50psi, so you don't need the 1st stage regulator, you just need the 2nd stage regulator that you use to breathe on.
And you obviously don't own a tank full of air either.
 

archer1960

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I agree that it can be confusing if in fact there is a difference between training (recommended) depth and certification depth.

If I was at home I would pull out my OW book and see what it states there but I did find this from the PADI website:

"Beginning scuba divers stay shallower than about 18 metres/60 feet"

"Beginning" <> "OW Cert"
 

archer1960

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I'm not diving with hookah. I'm using the regular AL80 3000psi tank strapped on my back. When the tank pressure down to 150 psi, that's the minimum pressure drop that my Scubapro MK25 need to deliver intermediate pressure to my S600 2nd stage regulator. Basically the MK25 regulates the tank pressure from 3000 psi to 150 psi before going to the low pressure hose and to the 2nd stage regulator.

Your compressor can only put up 50psi, so you don't need the 1st stage regulator, you just need the 2nd stage regulator that you use to breathe on.

Your description is correct as far as it goes, but it doesn't go far enough. Your 1st stage will continue to open until the IP reaches its 150psi set point. If it can't reach 150, it keeps trying, by simply going full open and staying there. Your 2nd stage works similarly. If it can't keep the downstream pressure it wants to, it simply opens all the way and stays there. So you can breathe your tank down until its internal pressure is equal to the ambient pressure at your 2nd stage.
 

Dan

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Your description is correct as far as it goes, but it doesn't go far enough. Your 1st stage will continue to open until the IP reaches its 150psi set point. If it can't reach 150, it keeps trying, by simply going full open and staying there. Your 2nd stage works similarly. If it can't keep the downstream pressure it wants to, it simply opens all the way and stays there. So you can breathe your tank down until its internal pressure is equal to the ambient pressure at your 2nd stage.

What happen when the tank itself bleeds down & reaches 150psi? Can you get air in the lP hose, downstream of the 1st stage regulator? What is the minimum pressure in the tank required to be to open the 1st stage regulator? I thought there is a minimum of 150 psi to push open the piston & spring to vent the tank pressure to the IP hose. So if the tank pressure is less than the pressure required to push open the piston, then, there won't be any air bleed out of the 1st stage into the IP hose. Am I missing something?
 
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archer1960

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What happen when the tank itself bleeds down & reaches 150psi? Can you get air in the lP hose, downstream of the 1st stage regulator? What is the minimum pressure in the tank required to be to open the 1st stage regulator? I thought there is a minimum of 150 psi to push open the piston & spring to vent the tank pressure to the IP hose. So if the tank pressure is less than the pressure required to push open the piston, then, there won't be any air bleed out of the 1st stage into the IP hose. Am I missing something?

No, you have it backwards. It's the pressure downstream of the 1st stage regulator that CLOSES the valve. If the tank doesn't have at least 150 psi in it, a spring fully opens the valve, and your LP hose and 2nd stage receive whatever pressure is left in the tank. The 2nd stage works similarly, where it will deliver air until the pressure in the hose gets down to (almost) the ambient pressure in your mouth.
 

BRT

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No, you have it backwards. It's the pressure downstream of the 1st stage regulator that CLOSES the valve. If the tank doesn't have at least 150 psi in it, a spring fully opens the valve, and your LP hose and 2nd stage receive whatever pressure is left in the tank. The 2nd stage works similarly, where it will deliver air until the pressure in the hose gets down to (almost) the ambient pressure in your mouth.

Thanks Archer. I hate for someone to sound like they know what they are talking about and teach things that are not true.
 
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