Suunto Cobra 3 500 psi safety reserve.

[ScubaSteve1962]

How do you treat this feature on a Cobra 3, because of me not reading my manual thoroughly, I'm not as big an air hog as I thought I was, This means I haven't ended a dive with less than 500psi. Should I still continue on as I have, or let my computer drop close to zero with the reserve?

The remaining air time calculation includes a 35 bar/500 psi safety reserve. This means
that when the instrument shows the air time to be zero, there is still about 35 bar/500 psi
of pressure left in your cylinder, depending on your air consumption rate. With a high
consumption rate, the limit will be closer to 50 bar/725 psi and with a low rate closer to 35
bar/500 psi.

 

[NCadiver]

If you are diving on a charter they will want to see the 500psi.

 

[ScubaSteve1962]

If you are diving on a charter they will want to see the 500psi.

If they put a gauge on it they will see it.

 

[thirdcoastdiver]

I believe the computer will show the correct tank pressure, but the air time will be zero between 500-750 psi depending on your SAC.

 

[altaskier]

I believe the computer will show the correct tank pressure, but the air time will be zero between 500-750 psi depending on your SAC.

What he said - almost. I once finished a shore dive in 15 feet of water with very little air (a photographer got separated from the group and we were looking for him - turns out he joined another dive team inadvertently so all ended up OK). My Cobra 3 was showing 10 bar/150 psi, and then suddenly it showed zero pressure, at which point I surfaced. Yes, I know, not good diving practice, and not good for the tank...

 

[ScubaSteve1962]

I believe the computer will show the correct tank pressure, but the air time will be zero between 500-750 psi depending on your SAC.

When compared to gauges on my last dive, there was a 500 psi difference on 2 tanks, and at times when it has shown below 500psi, the remaining air time was not zero.

Is there a gauge that you can just hook up to the tank to check the pressure?

 

[NCadiver]

If they put a gauge on it they will see it.

They usually don't have a gauge on board because they have your gauge to use.

 

[altaskier]

When compared to gauges on my last dive, there was a 500 psi difference on 2 tanks

One thing to keep in mind is the effect of temperature on tank pressure. For example, a tank just off of the compressor with the gas at 110 F will lose 200 PSI when you jump in to 70 F water, and 300 PSI when you jump in to 50 F water. For a while I was wondering why I was blowing through so much gas in the first 2-3 minutes of every dive...

Also, precision (the ability to make a reading to many digits) does not equal accuracy (the correctness of the reading). Or as they say, a man with two watches never knows what time it is.

I can say this: the Cobra 3 does not subtract 500 psi from the true value when displaying your tank pressure. Can't say what the absolute accuracy of its pressure gauge is, or the absolute accuracy of a spring calibrated analog gauge on a dive boat.

 

[Skooter]

The air time remaining will hit zero at your selected preset reserve pressure, you choose whether that is 100 psi or 1000 psi or ? So it will say zero at 100 psi or 1000 psi or whatever you set your reserve pressure at. It is calculating down to zero at your reserve tank pressure.
The tank pressure above the bottom left button will always be your exact tank pressure. If you are getting conflicting readings from the tank pressure then I would have it checked out.