Cylinder pressure anomaly

[JC]

My wife and I both use Aladin Air. On a recent dive trip to Belize I ran into a problem that I am having difficulty finding an answer,It appeared that i was always being given cylinders with quite a bit less air than my wife's I was giving the dive operators a hard time abut this }
They insisted that this was not so and we made the following checks over the
next couple of days:
1] Checked any new cylinder both against my wife's Aladin Air and my own,
2] Checked both my wife's cylinders and my own against two spg's.Her computer tallied with the spg readings.
On every occasion the pressure reading on my computer was always less varying from 6 - 10 bar .
Could not see any obvious reason why this was occurring. Temperature of all the cylinders being compared I reckon was the same.
Anyone out there with a similar experience or can shed light on this anomaly. Scubapro have just checked the unit over and say they can find nothing wrong with it.

 

[Aardal]

:idea:

This is pretty easy to explain and when you think about it, it will all make sense. The reason that you run out of air first is because a womens body won't consume/need alot of air to circulate through her blood. Her muscles don't need as much oxygen as a Males body does. Another factor to take into consideration is that your body is larger and muscular to move your body, so there for your muscles need more oxygen to function. I would say its normal for a women diving same size tank would have about 500-750 psi more at an end of a dive than the avg male would. So its not anyone playing tricks on you or your diving equipment isn't working properly. You will find that this is a common thing with male female dive buddies. The same thing happens when I dive with my wife. Good Question and I hope this helps!

Dive safe....

Aardal

eace:

 

[WetDane]

Aardal,
youøre right - to an extent, because you are also assumng that the checks were done based on time i water and not as I think prior to entry -
I would like to know if the pressure check was done before entering the water and with both the computer and a SPG?

Terkel

 

[JC]

Yes, Correct. Prior to entering water. These were checks on cylinder pressures as normal as part of normal checks. Not post dive.
Thereby lies the problem.
John

 

[Aardal]

JC :idea:

I understand what your saying now. I was thinking all post dives. Do you both have the same regulator setup? Some require more air to fill the system but I wouldn't think it would be 6-10 Bar difference. Let me think about it some more and I will get back to you on this. It is mind boggling. A few more questions though. Does your SPG check out the same with your computer? and I assume both SPG were reading the same?

Aardal

 

[Maggie]

I noticed the same when I first got my Aladin Air X Nitrox computer. According to the book the computer will always display pressure converted to a temperature of 20 degrees C whereas the mechanical depth guage displays the pressure influenced by temperature.

 

[JC]

Yes, spg's the same. Temp influence the same. One corelates with the spg, but, the other not. I must admit it baffles me.

 

[LesleyDSO]

Air pressure varies at different temperatures, the hotter the air the greater the pressure. If you check the pressure of a newly filled tank that is still quite warm, against the same tank when it is cold, the pressure will have reduced. We all know the situation of jumping in the cold water to have our full tank take a drop in pressure as it aclimatises to the water temperature. To avoid this problem and give you a consistent reading, your Aladin Air converts the pressure in your tank to what it would be at 20 degrees no matter what the temperature inside or outside the tank. Your wife's SPG cannot do this.

 

[LesleyDSO]

JC, I just reread your post and noticed you both use an Air. I guess in that case it's just a small variation, that can be fixed by calibration. I'm not sure what the allowable variation percentage is on these computers. I had one that started reading low when I was in Truk Lagoon (about 15bar). Over the next month it got worse, up to about 30bar, so I sent it away to be fixed. With yours, you know about it, it's reading low, meaning you have a little more air than you thought, and it's consistent (meaning the oil is not leaking) so I wouldn't worry too much. If you are, see your Uwatec dealer.

 

[JC]

Thanks LesleyDSO, I guess, this is the most probable reason. It just seemed strange that it was OK previously and then on this trip ut started giving the low readings. You're right, of course, as long as you know what it's doing it'ts not a problem in that sense.