First Rebreather Questions

[piranhaman00]

Great discussion! Back on topic!

Do mCCR have any batteries? I am going to be going with the shearwater HUD, where does this get power from? I am assuming the o2 sensors need some voltage applied to them.

I understand with eCCR there is a battery pack to power solenoid. Curious if mCCR have battery at all.

 

[flymolo]

Great discussion! Back on topic!

Do mCCR have any batteries? I am going to be going with the shearwater HUD, where does this get power from? I am assuming the o2 sensors need some voltage applied to them.

I understand with eCCR there is a battery pack to power solenoid. Curious if mCCR have battery at all.

hud and handset have batteries, sensors do not. The sensors generate an electrical current from oxygen and the hud and handset measure that current and convert into po2.

 

[Wibble]

Great discussion! Back on topic!

Do mCCR have any batteries? I am going to be going with the shearwater HUD, where does this get power from? I am assuming the o2 sensors need some voltage applied to them.

I understand with eCCR there is a battery pack to power solenoid. Curious if mCCR have battery at all.

A manual CCR means there's no automatic oxygen injection, i.e. no solenoid. This means there's no "controller" for that solenoid and the computer(s) are simply monitors (with batteries). Manual CCRs still have all the oxygen monitoring electronics; three cells or more with the computers to display the levels, either as a display or a flashing light head-up display (HUD).

Obviously the oxygen levels will decrease as you breathe which is why an electronic CCR has a solenoid injecting every, say, minute to restore the oxygen levels to your chosen setpoint. With a manual CCR you would need to manually add the oxygen using the oxygen manual add valve.

To reduce the speed that the oxygen decreases, manual CCRs have an "orifice" or needle valve which constantly trickles the oxygen into the loop at a rate that is just below the diver's resting oxygen consumption (quiescent metabolic rate). This means that the mCCR diver only has to inject every few minutes or so (depth changes aside). Some rebreathers have both a solenoid and an orifice, called a hybrid rebreather or hCCR (Revo, FX-CCR), to reduce the amount of injection by the solenoid.

One large benefit of the orifice is to counteract the buoyancy changes when the solenoid injects especially when shallow in an overhead environment -- a solenoid injection may push you to the ceiling!

When at decompression on my Revo, the orifice provides all the oxygen I need without dropping the setpoint. If you've a full eCCR, the solenoid will inject every minute or so, consuming the solenoid battery.

 

[flymolo]

A manual CCR means there's no automatic oxygen injection, i.e. no solenoid. This means there's no "controller" for that solenoid and the computer(s) are simply monitors (with batteries).

Obviously the oxygen levels will decrease which is why you have a solenoid injecting every, say, minute. With a manual CCR you would need to do this with the oxygen manual add valve.

To reduce the speed that the oxygen decreases, manual CCRs have an "orifice" or needle valve which constantly trickles the oxygen into the loop at a rate that is just below the diver's resting oxygen consumption (quiescent metabolic rate). This means that the mCCR diver only has to inject every few minutes or so (depth changes aside). Some rebreathers have both a solenoid and an orifice, called a hybrid rebreather or hCCR (Revo, FX-CCR), to reduce the amount of injection by the solenoid.

One large benefit of the orifice is to counteract the buoyancy changes when the solenoid injects especially when shallow in an overhead environment -- a solenoid injection may push you to the ceiling!

When at decompression on my Revo, the orifice provides all the oxygen I need without dropping the setpoint. If you've a full eCCR, the solenoid will inject every minute or so, consuming the solenoid battery.

If you dial in the needle valve to match your metabolic rate the po2 wont change unless you increase or decrease your workload. It sounds tricky but in reality it’s not and you can often go quite a long time without having to push any buttons at all.

 

[davehicks]

Great discussion! Back on topic!

Do mCCR have any batteries? I am going to be going with the shearwater HUD, where does this get power from? I am assuming the o2 sensors need some voltage applied to them.

I understand with eCCR there is a battery pack to power solenoid. Curious if mCCR have battery at all.

No batteries in the mCCR and no digital electronics. The oxygen cells are actually chemical fuel cell batteries themselves. In the presence of oxygen they generate voltage that is then read by the external dive computer for the PO2 monitoring. More oxygen, higher voltage. They last 1-2 years then need to be replaced whether you use them or not.

My first mCCR almost 20 years ago didn't even have a connected computer. Just an analog LCD display of the raw PPO2 values from the cells. You used a separate dive computer that depended on assumed target set point values that the diver was responsible for maintaining.