In this post, there will be the pros and cons of using a rebreather, a brief description of how a one works and a more detailed description of three reputable models that are readily available (that is in stock, not in development or more difficult to locate). There is a lot of technical information to digest, so a number of videos that specifically demonstrate each model are provided. In addition, more in-depth articles are linked to fill in the gaps and put you in a better position to decide how to proceed.
From the negative point of view:
- Rebreathers are expensive.
- There are also potential safety issues that need to be addressed by getting professional training before using one.
- Rebreathers are in some aspects inconvenient, though it can be argued these are made up for in their benefits.
On the positive side:
- Diving is bubble-free. You’re no longer noisy and intruding on the natural environment to the extent you are with open-circuit systems.
- Buoyancy is not affected by breathing.
- It is more comfortable to breath warm, moist gas compared to that of standard scuba systems.
- Gas use is decreased as consumption is determined by metabolism not depth, so normal use is only about 1 liter per minute.
- There is no predive gas mixing for different target depths.
- Oxygen levels that can be adjusted at every depth can increase bottom times.
- No decompression bottom times can be extended significantly.
- If decompression is required, 02 rich gas shortens stop times.
How Do Rebreathers Work?
A rebreather is a fairly sophisticated piece of technology. You should have reasonably detailed knowledge of how it does its job and you will need to be on top of physiology and diving physics.
All rebreathers do basically the same thing: remove excess CO2 from the breathing loop while adding the necessary amount of oxygen or nitrox to create the desired mix.
You will need to commit to the proper care and maintenance of your rebreather. Otherwise, the risk of equipment malfunction would put you at significant risk which could lead to death.
Types of Rebreather
The most common type of rebreather is closed circuit. Semi-closed circuit rebreathers are also still available. This type loses some gas on each exhalation and keeps a constant percentage of oxygen, unlike the fully closed units. These are more suited to recreational depths than decompression dives. In one of the videos below (the first Kiss Classic Explorer video), there is an introduction to a semi-closed circuit system as an example.
Also, there is a choice between an eCCR or an mCCR. The “e” stands for electronic and the “m” stands for manual. This is regarding how the oxygen is inserted into the breathing loop.
Electronic Closed Circuit Rebreathers (eCCRs) use a computer to continuously measure how much oxygen is in the breathing loop and automatically maintains it at the PPO2 (partial pressure of O2) set point.
Manual Closed Circuit Rebreathers (mCCRs) need the diver to monitor the PPO2 level manually and inject more oxygen when needed to maintain the oxygen content at the proper level. These types are simpler and less expensive, but require an increased level of awareness and diligence on the part of the diver.
Scrubber and Counter Lung Design
The scrubber canister is an essential component of a rebreather. This contains a chemical that removes the excess CO2 from your breathing loop. There are two types of scrubbers.
Axial: This involves a cylindrical shaped pipe where the gas passes vertically.
Radial: The gas passes from the middle of the canister toward the outer sides in a radial direction.
Counter Lungs: These are bag like components in the breathing loop. They can be either back-mounted or over the shoulder. When they are back-mounted, the chest area is free of clutter, but this location makes it easier to exhale and harder to inhale. Counter lungs come in different sizes that you will need to decide which fits you best.
That is a basic introduction to rebreathers. There is a lot more information available to enhance your knowledge, fill in some gaps and give you a broader perspective. Here are two relatively short, but thought-provoking articles to check. Click on the titles you want to read.
Rebreather Descriptions and Reviews
Kiss Rebreathers have a line of 5 closed-circuit rebreathers and 1 semi-closed circuit model. Below I will highlight the two tried and true warhorses of their line, the Orca Spirit and the Classic Explorer. For really complete descriptions, specs, etc., click on this link to their website:
The third rebreather described below is the Hollis Prism 2.
Fully assembled and ready to go, the Kiss Orca Spirit is just 23 inches tall ( 5 inches shorter than an aluminum 80) and at the most 13.5 inches wide. It also has a narrow profile with the unit sitting just six inches off the diver’s back when the harness and wing are attached. The diluent is supplied by a side-mounted off-board cylinder that can be mounted the way most CCR divers carry their bailout bottle.
This is an mCCR system, so oxygen adjustments are manual requiring the diver to be alert and vigilant to maintain safety. Scrubber life is a reasonable 3.5 hours and the counter lungs are a wrap-around design that results in ease of breathing and good horizontal trim when diving in a wetsuit.
Specifications (from Kiss):
- 300 fsw / 91 msw depth rating
- bi-axial design scrubber type
- 6.2 pounds with molecular 797 sofnolime scrubber capacity
- 8 Liters maximum counterlung capacity
- 23 inches x 13.5 x 6 (58.4 cm x 34.2 x 15.3) dimensions
- 42 pounds / 19 kg weight
For a full manufacturer’s description click here:
This is another mCCR system from Kiss which requires diligence on the part of the diver to manually add oxygen when needed. Introduced in 1999, Classic is an appropriate name for this durable, reliable and easy-to-maintain unit.
Its configuration is straightforward with the rebreather’s head and scrubber centrally positioned on the diver’s back and oxygen and diluent supplies mounted in tanks on either side. This layout follows that of the majority of rebreathers built today. The two counter lungs are back-mounted and the scrubber has a relatively shorter duration of approximately 2.5 hours.
Specifications (from Kiss):
- 300 fsw / 91msw depth rating
- Axial design scrubber type
- 5.7 pounds – molecular 797-grade sofnolime scrubber capacity
- 8 Liters maximum counterlung capacity
- 21 inches x 14 x 8 (54 cm x 36 x 20)
- 51 pounds. 22 kg
For a full manufacturer’s description click here:
The Prism 2 is a fully modern electronically controlled, constant PO2, modular, closed-circuit diving system (eCCR) that is a highly reputable platform for divers to explore the technical underwater world.
Diluent and O2 bottles are mounted on either side of the scrubber canister with electronics and the battery housed on their own outside of the breathing loop. Battery life is 40 hours at 70 degrees F (21 degrees C).
Counter lungs are mounted over the shoulder decreasing the work of breathing. There are also three O2 sensors and an alternate inflator for the diluent bailout.
There are literally dozens of videos on YouTube that cover every aspect of the usage of the Hollis Prism 2.
I hope you found this post on closed-circuit rebreathers interesting and useful. If you have any questions or ideas, please feel free to share them in the comments section. If there is no comments section directly below, click here:>>comments<<