Why aren’t scrubber monitors (aka TempStick) standard on all rebreathers?

[Wibble]

Only two popular rebreathers have scrubber monitors; AP Inspiration and Revo.

These monitors provide excellent information about the status of the scrubber time left for the diver to make decisions based on facts rather than assumptions.

Why is this? It’s not like voodoo as the scrubber chemistry is exothermic.

 

[Whitrzac]

Because the rebreather works without them.

Why add another failure point to the device keeping you alive?

 

[rddvet]

Because they’re unnecessary and temperamental. If I was required to have one stock from my ccr manufacturer I would likely remove it or find a different ccr.
They’re an unnecessary gimmick in my book

 

[Wibble]

Because the rebreather works without them.

Why add another failure point to the device keeping you alive?

It's worthy information though.

For example the Revo has a 3h duration to swap out one scrubber, or a 3h45 to swap both.
In warmer water this can easily work for over 5h according to the RMS (Revo Monitoring System / TempStick). This is affected by workload and the indicated scrubber time remaining will drop and extend during a dive.

Isn't that better than relying on rules of thumb, especially for challenging or long duration dives? Thinking of that 110m/360ft dive on another thread. The JJ has a limit of 3h, but that dive would go for longer all other things being equal.

 

[tbone1004]

It's worthy information though.

For example the Revo has a 3h duration to swap out one scrubber, or a 3h45 to swap both.
In warmer water this can easily work for over 5h according to the RMS (Revo Monitoring System / TempStick). This is affected by workload and the indicated scrubber time remaining will drop and extend during a dive.

Isn't that better than relying on rules of thumb, especially for challenging or long duration dives? Thinking of that 110m/360ft dive on another thread. The JJ has a limit of 3h, but that dive would go for longer all other things being equal.

because the hour limits set by the mfg's are under insane workload conditions and really high gas densities. If you are experienced enough to be doing a 100m+ dive then presumably you know your unit fairly well and you also know the ratio of O2 consumed to CO2 used which magically happens to be around the same volume of a 3l of O2..... My general rule of thumb is when my O2 is out, so is the sorb.

The tempsticks are nifty and I'm not going to say that I don't like the information when I'm diving an APD but I also can't say that it changes the way I dive or would be something that even makes a list of do I choose this ccr or that one.

 

[kensuf]

I find the tempstick on my Inspiration provides some fascinating info, especially wrt bed depth. Watching it move back to the left when I get to shallow deco stops is neat. But, because I'm pretty conservative when it comes to sorb, I don't feel like I need one on my other units.

 

[broncobowsher]

I had this discussion when I ordered up my rEvo. The decision was to go without. It was seen as a way to ignore the proven guidelines on sorb life and push the sorb to the limits. Yes there may be live in a scrubber after the 3 hour rated use, but treat that as a redundancy feature for when things go really wrong. Not a good way to save $20.

Wibble points out, gets 5 hours out of a 3 hour fill. But how reliable are those last 2 hours?

The correct use of a temp stick is to make sure you are not getting an early break through. If there is reaction deep in the bed while early in the run cycle. That is what the temp stick is there to catch. The problem is people are not using the temp stick as it should be used (early breakthrough detection) and it is used as a gas gauge to see how close to empty you can get.

 

[boriss]

Because they’re unnecessary and temperamental. If I was required to have one stock from my ccr manufacturer I would likely remove it or find a different ccr.
They’re an unnecessary gimmick in my book

They're definitely not a gimmick! The probes work and here's a paper on the subject: The performance of ‘temperature stick’ carbon dioxide absorbent monitors in diving rebreathers

"These data represent the first publicly reported demonstration that temperature sticks can reliably warn indirectly of CO2 breakthrough before it occurs."

 

[Wibble]

The standard pre-jump procedure with a Revo with RMS is to pre-breathe the unit to show a minimum of 45 minutes on the scrubber indicator (integrated into the Petrel). This shows that the scrubber's warming up through the CO2 reaction.

AFAIAC, this means: that the unit is basically working; that the scrubbers are installed (will show xx if they're not); that the scrubbers have 'sorb in them; that it's an indication that the 'sorb isn't expired.

It won't detect a leaky mushroom valve (unless it's completely folded). It only knows where the scrubber front is.

By the time you've waddled over to the back of the boat the scrubber time will be well over an hour and by the time you reach the bottom it'll show the estimated full time of 3h (to cycle).

It's not bullet proof by any means. But it's a great indication that the box of death is currently working to some extent or other.

Also, the Petrel shows a scrubber page with the previous dive's ending scrubber times.



My opinion is that I'm happier with that scrubber indication than without. It's an indication that it's working, not proof that it's working, nor proof that it's not passing CO2. On my bailout earlier this year when the scrubber was flooded (completely my fault) I do not remember the RMS dropping or warning me.

After any but the most trivial of dives, say less than an hour and not deep, I'll always cycle the scrubbers (i.e. move the bottom scrubber to the top, refill the the top scrubber, put it in the lower position). As this entails ditching 1.3kg/3lbs, it's not normally expensive.

 

[mr_v]

@Wibble - market demand. Most manufacturers won't create things that won't succeed in the broad market. As seen in this thread, many divers don't want to pay for extras. As there are no regulations that mandate CO2 sensors or temp sticks, it is a simple decision.

The lack of a strong market demand does not diminish the value of temp sticks or CO2 monitors. These devices are not to tell you how long the scrubber will last but to alert you before things go south. If I had a temp stick in my rEvo, I'd still cycle sorb as advised.