[Bevan]

My O2 tank is 15 cu ft and should be good for about 7 hrs at 1.0 litre/min. Full tank indicated 2000 psi. After a couple hours of use, the tank reads about 1000 psi. Is this a quirk of O2 tank pressure/ temperature or am I really down to half full? such as a bad regulator or a leak.

Bevan

 

[Mike S]

Using the O2 caused the cylinder temp to drop.

Cylinder temp going down causes the internal pressure to drop.

Look up Boyle's law, pretty sure that is the one dealing with such.

All that said, not sure if the changes due to Boyle are enough to make that much of a difference in gauge readings.

 

[BobTurner]

Using the O2 caused the cylinder temp to drop.

Cylinder temp going down causes the internal pressure to drop.

Look up Boyle's law, pretty sure that is the one dealing with such.

All that said, not sure if the changes due to Boyle are enough to make that much of a difference in gauge readings.

A lot more common is the opposite: the filler rapidly fills the tank, and it gets quite warm, reads 2000 psi. A few hours later it reads less.
It's just proportional to the absolute temperatures. So a warm day = 300 K; freezing at altitude = 270 K; so about a 10% pressure change.
The typical flow gauges aren't all that accurate. maybe you were using 1.5 l/min instead of 1?

 

[flightlogic]

After you get the readings worked out.... try an oxymiser cannula and pediatric regulator. All under 60 bucks. Coupled with a finger tip monitor... you might find you are wasting most of your oxy right now with your setup. BTW, you won't ever see the 3000 psi the tank is rated for... unless you transfill yourself.

 

[RV8Squaz]

My O2 tank is 15 cu ft and should be good for about 7 hrs at 1.0 litre/min. Full tank indicated 2000 psi. After a couple hours of use, the tank reads about 1000 psi. Is this a quirk of O2 tank pressure/ temperature or am I really down to half full? such as a bad regulator or a leak.

Bevan

Here's a link to an oxygen duration chart on Mountain High's website:

http://www.mhoxygen.com/index.php/component/attachments/download/627

How much oxygen you use will greatly depend on your flowmeter, cannula (or mask), and your altitude. Your cylinder is similar to MH's AL-415 (14.7 cu ft). As you can see from the chart using the MH4 at 1 l/min at 10K, you would expect a full bottle to last 5.8 hrs at 10K and only 4.0 hrs at 15K. So if you used it a couple of hours it certainly would be possible to see 1000psi. The pressure will come up slightly as the bottle warms back up.

I use the MH3 flowmeter and the oxymizer cannula and the pressure remaining in the bottle directly (linearly) correlates with how long I used it at the specific altitude. I have the AL-647 bottle which yields 14.8 man-hours at 15K with the MH3 and oxymizer cannula. I use my O2 system often and carry a laminated chart in my bag. I've come to know what to expect readily. If I use it for 3 hours at 15K it it will indicate about 1600 psi [ (14.8-3)/14.8 * 2000 ]. The two times when I've had less pressure remaining than what I expected was because of a leak. Also realize that when you get your cylinder serviced it will rarely be filled to 2000 psi.

I hope this helps.