Tank Volume and Pressure Equivalencies

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antique diver
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Re: Tank Volume and Pressure Equivalencies

Thu Aug 25, 2016 11:01 am

luis wrote:One important point is that if your tank is full, you should not store your cylinders in the winter in a cold garage or outdoors.

The compressed breathing air is supposed to be very dry, with a dew point of about -65 degrees F, but that dew point is for the air at ambient temperature. When the air is compressed the dew point goes up to about +10F to +15F depending on the fill pressure. My garage normally doesn’t get that cold in the winter, but it gets close.

If the cylinder gets that cold you can get condensation inside.


That's a great point that I never thought of, even though I deal with compressed air and air testing every day for fire departments! I am embarrassed that the thought never occurred to me... always learning something new from Luis!

BUT, lucky for me I am in Texas, where it seldom drops into the 20's, and even far less frequently into the mid-teens! So, in my sphere of reality it just doesn't seem to apply! Hooray for moderate winters here... one less thing to be concerned about. :D

I do appreciate the point you have made, and it made me realize why the dew point requirements seemed ridiculously low for our local temp conditions. It make sense to have one standard for the whole country.

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rhwestfall
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Re: Tank Volume and Pressure Equivalencies

Thu Aug 25, 2016 11:40 am

I've had more of an issue with the severe cold resulting in gas leaking as the seat must be contracting to a point it isn't sealing....
Bob

No Longer Awaiting my Kraken.....

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luis
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Re: Tank Volume and Pressure Equivalencies

Thu Aug 25, 2016 12:21 pm

luis wrote:One important point is that if your tank is full, you should not store your cylinders in the winter in a cold garage or outdoors.

The compressed breathing air is supposed to be very dry, with a dew point of about -65 degrees F, but that dew point is for the air at ambient temperature. When the air is compressed the dew point goes up to about +10F to +15F depending on the fill pressure. My garage normally doesn’t get that cold in the winter, but it gets close.

If the cylinder gets that cold you can get condensation inside.


I am glad you all understood what I meant and not what I wrote. :shock:

Here is a correction of the second sentence shown above.
The compressed breathing air is supposed to be very dry, with a dew point of about -65 degrees F, but that dew point is for the air at ambient pressure.


The major reason for very dry air is to keep the regulators and valves from freezing due to the air cooling during the gas expansion. The starting temperature of the air in the cylinder is very important, but the adiabatic cooling that occurs during gas expansion can affect a regulator even in warmer air temperatures (even in Texas).

Avoiding condensation inside the cylinder is secondary, but a very important side benefit of having extremely dry air.
Luis

Buceador con escafandra autónoma clásica.

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antique diver
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Re: Tank Volume and Pressure Equivalencies

Sat Aug 27, 2016 9:09 am

rhwestfall wrote:I've had more of an issue with the severe cold resulting in gas leaking as the seat must be contracting to a point it isn't sealing....


With a diaphragm first stage cold weather can stiffen some older reinforced diaphragms to the point that the loss of flexibility can cause the intermediate pressure to rise to the point it pushes the second stage demand valve enough to make it leak. I ran into that years ago on some rental regulators, and solved it by replacing the diaphragms with softer ones from Mares MR12's. I don't recall for sure if the regs in question were Conshelf's or Dacor 300/350's. I think they were Dacor's before they started using a thinner diaphragm. Of course the same thing could occur in a two stage double hose reg with an old stiff 1st stage diaph.

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