FAQ ABOUT REBREATHERS
Open circuit divers considering transitioning to closed circuit diving need basic information about rebreather equipment and safety, course descriptions, costs and logistics. Without getting bogged down in too much detail, the best place to start may be to read our article Closed-Circuit Rebreather Instruction.
In our long experience, they are proven very reliable. The PSR series oxygen sensors are manufactured by Analytical Industries (now a division of Process Sensing), a major supplier in the rebreather market, who has been making our Dive Gear Express replacement sensors for the last 15 years.
By far the largest cause for reports of suspect sensors that otherwise turn out to be functioning normally is corrosion & contamination in the rebreather wiring and connector. We see approximately a 0.1% failure rate of successfully installed sensors (i.e. not counting those that were DOA due to g-force impact during shipping) or about 1 sensor per 1,000. We make an effort to retrieve failing sensors less than 12 months old for testing and microscopic examination by the factory. Some of the failures appear to be the result of exposure to excessive heat or salt water, or other mishandling such as impact in the rebreather itself. The most common cause of sensors becoming current limited early is the sensor was exposed to elevated oxygen levels for an extended period -- that typically happens when the breathing loop was not flushed completely with diluent following calibration (or was not aired out following diving) and then the rebreather sits unused.
For logistics reasons, our Customer Care team is unable to answer questions regarding specific dates of manufacture or expiration on products with limited shelf life such as: rebreather oxygen sensors with 6 month shelf life, CO2 absorbents with 60 month (five year) expiration dates, and cylinders with 60 month (five year) hydro re-test dates. We guarantee you will receive products dated well within current supply-chain norms: rebreather absorbent and cylinders will be less than two years from date of manufacture, oxygen sensors will be less than six months from date of manufacture.
We turn over our inventory frequently and can assure you that the products we ship are fresh.
Yes, Sofnolime™ 8-12 Mesh NI (Grade 797) is a suitable granular option for your Dive Rite and Poseidon rebreathers, as well as the Mares rEvo rebreather and almost all other sport and technical diving rebreathers.
The Dive Rite models with the 2015 packable/EAC scrubber can accept either granular or Extendaire cartridge, earlier versions can only accept the Extendaire cartridge. The Poseidon models originally used a Molecular cartridge that is no longer available and now accept a self packable granular canister.
We only stock and sell the smaller granule Sofnolime™ 812 Mesh (Grade 797) non-indicating absorbent designed specifically for use with all modern semi-closed and closed circuit recreational sport and technical diving rebreathers that require granular carbon-dioxide absorbent.
An absorbent grade used in commercial diving hyperbaric chamber systems is "Grade CD" which is generically referred to as 408 and typically lower cost but much less absorption capacity. Some very early rebreather designs may still specify 408 absorbent, but today this is rare. For a discussion of the differences between Grade 797 and Grade CD absorbent, see our TekTip titled CO2 Absorbent: 797 vs 812 vs 1025.
Divers Supply Inc in Gretna, LA (not to be confused with a different company by the same name in Florida) is a popular source for 408 mesh Commercial Diving grade indicating absorbent.
The primary difference today from the user standpoint is that the Poseidon Se7en+ electronics module has been updated to include native support for Poseidon's optional Solid State Oxygen Sensor. Due to improvements in gas injection the Se7en+ design now requires three instead of four solenoids, theoretically improving reliability by reducing parts count. There also are some internal differences that make the e-module easier to manufacture, assemble and service at the factory. Support for granular absorbent (in the form of a self-pack cartridge) is also now included as standard on the Se7en+ model, as the pre-pack cartridge has been discontinued.
The typical intermediate pressure setting for most first stages is around {135 psi | 9.5 bar}. Upon request a Dive Gear Express service technician will adjust the IP to your specified non-standard setting prior to shipment but only for diaphragm first stage designs. We also offer 3rd party modifications to the Apeks DS4 to change the behavior of the intermediate pressure; enabling use with constant mass flow orifices and needle valves found on some types of rebreathers.
The IP adjustment on diaphragm type first stages is simple enough for most divers to learn to do themselves. The IP adjustment screw is located under the environmental seal cap on the bottom of the regulator. The only tools needed are a round surface spanner wrench to remove the cap, a hex key set to turn the adjustment screw to change the IP setting, and an IP pressure gauge to measure the setting. These are all available in our Regulator Service Tools category. A few minutes with a knowledgeable peer or Google will show you how.