Sensors: which gas shall I have in the loop when not in use?

[happy-diver]

Understanding_oxygen_sensors.pdf

Understanding-Oxygen-Sensors-part-II_the-complete-picture.pdf

 

[Agro]

Both links do not work

 

[happy-diver]

So make them work

 

[Gareth J]

As others have said.

• O2 Cells do not like humid environments. (There are a number of engineering changes to CCR O2 cells, that include membranes etc to mitigate this).
• Rebreathers need to be cleaned and rinsed after use. (Two or three days without rinsing in a temperate environment is ok.) After a long weekends diving my unit is immediately broken down and rinsed. If I can, before I leave for home. If not, at the latest, first thing the following morning.
• Irrespective, once diving is finished, I pull the head off to allow it to dry.
• When not in use, the rebreather is stored in its component parts. Its better for the O-rings, ensures things are properly dry.
• The Day before use, the unit is carefully rebuilt. Each O-ring checked, negative/positive pressure testing, and the cells recalibrated and checked for drift.

Note - New cells need to 'wake-up', the inert gas stops/slows the chemical reaction, which extends the stored life. The problem is, once unpacked, O2 cells take time too stabilise. If a cell is unpacked and used immediately, the calibration is unreliable. (Easily demonstrated as the PO2 appears to drift on the new cell when compared to the other two).

It is generally preferred that O2 cells are changed at different times, rather than all at the same time.
This ensures that you have at least two cells that have a high chance of being 'reliable'.
If I have to change them all in one hit, I am very conservative on the next few dives. Checking the PO2's at the start and end of the dive in 6m, and diving a low PO2 during the dive phase.

In the old days, when I first started using Nitrox back in the 90's. We used to put the O2 meter / cell, in an air tight container. We soon realised that it did little to extend the life. Any drift issues had minimal effect because the meter was calibrated and used within minutes of the calibration, so changes in cell behaviour had minimal impact.
The best bit about putting the meter/cell in an airtight container. It kept it dry, and offered some protection from some idiot dropping a cylinder on it.

There are two golden rules of CCR diving.

1. Know your PO2 at all times!
2. You need to be pedantic about maintenance, assembly and testing the unit.

Failure to follow these two rules means at best, missed dives, at worst, death.

 

[Agro]

As others have said.

• O2 Cells do not like humid environments. (There are a number of engineering changes to CCR O2 cells, that include membranes etc to mitigate this).
• Rebreathers need to be cleaned and rinsed after use. (Two or three days without rinsing in a temperate environment is ok.) After a long weekends diving my unit is immediately broken down and rinsed. If I can, before I leave for home. If not, at the latest, first thing the following morning.
• Irrespective, once diving is finished, I pull the head off to allow it to dry.
• When not in use, the rebreather is stored in its component parts. Its better for the O-rings, ensures things are properly dry.
• The Day before use, the unit is carefully rebuilt. Each O-ring checked, negative/positive pressure testing, and the cells recalibrated and checked for drift.

Note - New cells need to 'wake-up', the inert gas stops/slows the chemical reaction, which extends the stored life. The problem is, once unpacked, O2 cells take time too stabilise. If a cell is unpacked and used immediately, the calibration is unreliable. (Easily demonstrated as the PO2 appears to drift on the new cell when compared to the other two).

It is generally preferred that O2 cells are changed at different times, rather than all at the same time.
This ensures that you have at least two cells that have a high chance of being 'reliable'.
If I have to change them all in one hit, I am very conservative on the next few dives. Checking the PO2's at the start and end of the dive in 6m, and diving a low PO2 during the dive phase.

In the old days, when I first started using Nitrox back in the 90's. We used to put the O2 meter / cell, in an air tight container. We soon realised that it did little to extend the life. Any drift issues had minimal effect because the meter was calibrated and used within minutes of the calibration, so changes in cell behaviour had minimal impact.
The best bit about putting the meter/cell in an airtight container. It kept it dry, and offered some protection from some idiot dropping a cylinder on it.

There are two golden rules of CCR diving.

1. Know your PO2 at all times!
2. You need to be pedantic about maintenance, assembly and testing the unit.

Failure to follow these two rules means at best, missed dives, at worst, death.

OK, OK, I got it. In future I will break down the unit right after dive and store the cells in air.

The question if cells shall be changed at a different time or all together is an old one. If we want to discuss this interessting point we probably should open a new thread.

The rest is clear anyway: know pO2, maintance, assembly, testing. My definition of rebreather: gas prolongation apparatus, sitting in your neck, trying to kill you.

 

[Wibble]

There are two three golden rules of CCR diving.

1. Know your PO2 at all times!
2. You need to be pedantic about maintenance, assembly and testing the unit.

Failure to follow these two rules means at best, missed dives, at worst, death.

3. Use checklists to avoid missing steps

 

[Agro]

3. Use checklists to avoid missing steps

Liberty has checklist in the menu, great thing.

 

[Wibble]

Liberty has checklist in the menu, great thing.

For building the unit? Does it include analysing the gas & pressure? Checking your bailout gas and regulators? Checking and greasing O-rings? Over pressure valves on wing and lungs? Checking weights, lights, suit inflate?

(This from memory— the build AND close checklists say much more)

 

[Agro]

For building the unit? Does it include analysing the gas & pressure? Checking your bailout gas and regulators? Checking and greasing O-rings? Over pressure valves on wing and lungs? Checking weights, lights, suit inflate?

(This from memory— the build AND close checklists say much more)

For building the unit? No, not for building, that's what you learn on the course by hart. Liberty's checklist tells you what to do after building.

Does it include analysing the gas & pressure? Yes, of course.

Checking your bailout gas and regulators? Yes, of course.

Checking and greasing O-rings? That's part of the building. If an O-ring is leaking, you find out during under- and overpressure test, part of checklist.

Over pressure valves on wing and lungs? Yes, of course.

Checking weights? Yes of course.

lights? Yes of course.

suit inflate? Yes of course.

 

[Agro]

So make them work

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