CCR FAQ - Poseidon Se7en+

Prepared by Mark Derrick, CCR Instructor on Staff

How much does a Poseidon Se7en+ cost?

A better wording of the question might be 'How much does it cost to switch from an open-circuit diver to a rebreather diver?' The price of the rebreather itself can vary significantly depending on configuration options. Plus there are usually additional equipment purchases depending on what existing gear you have that can be re-purposed. Training, particularly if travel is required, will be a significant cost. I suggest budgeting a total amount of about $15,000.00 minimum.

What is the difference between the Se7en+ and the Se7en?

Introduced in early 2020, the primary difference in the "plus" model from the end-user standpoint is the 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.

How long does it take to get a Se7en+ rebreather?

The rebreather base unit will usually be available for shipment within four to six weeks after receipt of order. Occasionally, demand or logistics will cause brief stock-outs of the base unit but delays beyond 30 days are rare. Accessories and spares are usually available for immediate shipment.

How much does the Poseidon rebreather training cost?

There is wide variation in training costs due to a variety of factors, although location (and thus indirectly the costs of instructor insurance) is often a major influence. There is a geographically diverse group of instructors and you might have an instructor in your local area. Typically, the cost ranges from $1500 to $2500 for instruction only, plus out-of-pocket costs. If you prefer to learn about your rebreather at Dive Gear Express in Pompano Beach Florida, training can be organized to accommodate your schedule and rebreather courses run every month.

Can I buy the rebreather without training?

Yes, but you won't be able to dive the rebreather until you are trained. Every rebreather requires formal, model specific, training in order to competently dive with the equipment; ordinary open-circuit training is not adequate. If you are not already certified for the rebreather, per manufacturer requirements you will receive a disabled unit that can only be enabled by your instructor. Once you complete training, your instructor will permanently enable your unit.

How much does routine maintenance cost?

You should budget routine maintenance costs of approximately $400 annually. Galvanic oxygen sensors should be replaced annually and the unit must receive a full service every 24 months. You will also need to replenish minor consumables such as lubricant and disinfectant from the annual maintenance budget.

What consumables do you recommend?

The recommended consumables are: Molecular Products Sofnolime Grade 797 loose 8-12 mesh granular carbon dioxide absorbent, Steramine for sanitizing the breathing loop, Tribolube 71 O2 Compatible Lubricant for O-ring seals, Caig Labs DeoxIT GOLD for cleaning gold electrical contacts, and Analytical Industries PSR-11-39-MD galvanic chemistry oxygen sensors.

How much do the consumables cost?

As with all rebreathers, the major consumable cost is CO2 absorbent. A self-pack granular absorbent load is about $25 and can typically can be used for several sport dives. There are other smaller costs such as gas fills. Keep in mind that for both open-circuit and rebreather divers, consumables costs are usually insignificant in relationship to the investment in the equipment, training and other diving costs such as boat charters and travel.

Is a pre-packed absorbent cartridge available?

Although the initial design of the Poseidon rebreather used a pre-packed absorbent cartridge called the "SofnoDIVE 797", as of late 2019 the manufacture by Molecular Products of those pre-pack cartridges was discontinued and they are no longer available. The Poseidon rebreather now has a re-usable self-pack scrubber cartridge that is included with all Se7en+ units and available as a separate purchase for use with existing Se7en units.

How long does the absorbent last?

When tracking their CO2 production by monitoring their oxygen consumption, divers are reporting scrubber duration in the range of four hours, if determining duration by wall clock time only then the absorbent duration is three hours. The duration in actual use depends upon many factors related to the individual diver and specific dive conditions. These are observations of what experienced divers are reporting and in no way suggests exceeding manufacturer recommendations or that novices should expect these durations.

What about the possibility of a 'caustic cocktail' with the Se7en?

Once you are trained, inhaling a mixture of CO2 absorbent and water while diving is very unlikely. The Se7en is a modern CCR design that includes several features to manage and remove water from the breathing loop. The 'caustic cocktail' is a concern from an earlier era of rebreather diving that has been overly dramatized, akin to the concern new divers express regarding 'shark attack'.

How available is the absorbent?

In the global economy, absorbents are sold and shipped all over the world. As a result, supply logistics for absorbent is becoming less of an issue. The number of dive shops that stock absorbent is consistently growing, and you can always order on-line to be delivered to your door or directly to your travel destination.

What about Solid State Oxygen Sensors?

The Se7en+ electronics module allows the choice of using either a traditional galvanic chemistry oxygen sensors and/or Poseidon Solid State Oxygen Sensors (SSO2). The SSO2 offers the benefits of no need for periodic annual replacement with greatly enhanced speed and stability. Currently, the SSO2 is believed to have an estimated life of about ten years but also costs about ten times more than a galvanic chemistry sensor. Dive Gear Express believes the SSO2 offers substantial improvements in convenience and reliability of oxygen measurement for divers. As of 2022, I recommend the Se7en+ be configured with one Solid State Oxygen Sensor as primary and one analog galvanic chemistry sensor as secondary.

Does the Se7en+ have a CO2 monitor?

No. Carbon dioxide monitoring is a 'bleeding edge' technology that will begin to appear in recreational rebreathers in the next few years but as a practical matter the merits of CO2 monitoring are unproven. You should not confuse a CO2 monitor with the breathing loop temperature monitor or the scrubber temperature monitor offered by rebreather manufacturers. The temperature monitor does not provide any information or warning regarding actual carbon dioxide levels in the breathing loop.

What Smart Module should I choose?

Poseidon offers a selection of different Smart Modules (identified by their color) that each enable software features which allow progressively more advanced levels of diving as well as providing power to the rebreather electronics. The basic Rec 40 (aka Green) Smart Module supports sport limits of no-stop required dives to a maximum of {132 fsw | 40 msw} on air diluent. Because these Smart Modules are expensive and time consuming to later upgrade, for divers who expect to exceed sport limits I recommend always initially choosing the Deep (aka Black) Smart Module that unlocks all functionality and has no depth or gas mixture restrictions.

What cylinders should I use?

The rebreather will accept 2L or 3L cylinder sizes using standard 'inline' DIN valves. For all divers, we recommend the Poseidon QMR cylinder mounting kit and inverted cylinder mounting (i.e. valves at the bottom of the unit to make them easier to reach.). Inverting the cylinders also will require some changes to hose lengths and fittings. Smaller stature divers may prefer the 2L cylinders and the 3L volume diluent cylinder has adequate on-board bailout capacity for sport diving in {60 ft | 20 m} or less, although I strongly recommend carrying off-board bailout on all dives. Aluminum 13 or 19 cubic foot (2L or 3L) capacity cylinders minimize the total weight, but most divers find they must add weight to adjust their in-water buoyancy and trim. The rebreather may also be configured with steel 17 or 23 cubic foot (2L or 3L) cylinders, and these are the cylinders I generally recommend. Most wetsuit divers find having the steel cylinders requires little or no additional weight and trim can usually be made perfect simply by slight adjustments to the mounting height of the cylinder.

Which style of counterlungs should I choose?

Over-The-Shoulder (OTS) vs. Back-Mounted (BMCL) counterlung configurations have subtle trade offs of one benefit for another, and the choice is more complex than can be answered briefly. Many professional photographers have a preference for BMCL, but for diving where performance and safety is paramount I recommend an OTS configuration with the manual addition valves option.

What BC should I use with the Se7en?

The Poseidon "jacket style" Rebreather BCD with integrated OTS counterlungs is a viable option for divers who expect to remain within recreational sport limits. However, we suggest a harness, backplate and wing (BPW) style system that mounts using standard 11-inch centers. We generally recommend the very comfortable Dive Rite TransPac, adding a ring bungee to sidemount your bailout. The Dive Rite CCR Wing has a shape and features that work well with the Poseidon and offers very low drag with{ 50 lb | 22.68 kg } of lift. Poseidon also offers a harness, backplate and wing BCD system if you prefer to remain with a single vendor. Regardless of your choice, you will require either the Poseidon BCD quick-mount-release option (recommended for sport) or the Poseidon 11-inch Adapter option (recommended for tech).

Does the Se7en accept an additional independent Oxygen sensor?

Technical divers will be pleased to know there is an option for adding an independent oxygen sensor to the inhalation side of the breathing loop. We can deliver your Se7en customized with a special third sensor adapter that connects to the Poseidon M28 handset or an independent Shearwater Petrel EXT dive computer.

What Se7en options are recommended for technical diving?

You will need the M28 dive computer with a CANbus cable to connect to the Se7en. You will need technical counterlungs with oxygen and diluent manual addition valves, along with cylinder inversion. You will need a third oxygen sensor with an integrated dive computer for independently monitoring loop PO2. I also now suggest that one of the three sensors be the solid state version. You will also need an in-line gas shutoff valve on the DSV/ADV/BOV gas supply. Technical divers using a wetsuit should have a BC with a redundant bladder option, or use a drysuit. I also suggest purchasing a second Deep (aka Black) battery module plus a charger.

What is the Se7en maximum dive time and depth?

Rebreathers carry many hours of breathing gas regardless of depth, so the dive time is rarely limited by gas volume. As with most rebreathers, the Se7en diver is typically limited by the duration of the CO2 absorbent, so multi-hour run time dives are routine. As with open-circuit nitrox diving, rebreather divers must also monitor their decompression and oxygen exposure; depending on the dive profile these may also limit the dive time. The Poseidon rebreathers are suitable for diving at all sport depths and the Se7en with the Deep battery has been qualified to a depth of {330 feet | 100 meters}. Although the Se7en can function at depths beyond sport depths, as with any rebreather there are numerous additional considerations.

Is the Se7en capable of diving with mixed gases?

Yes, the Se7en with the Deep (aka Black) battery can use either nitrox or trimix diluents that may be either hyperoxic, normoxic or hypoxic. Because the Se7en is a fully closed-circuit design, the use of mixed gas diluents is very inexpensive compared to open-circuit. Personally, I recommend and teach rebreather divers to substitute normoxic trimix diluent (21% oxygen, 35% helium) rather than air even within recreational sport limits for the benefits of reduced narcosis, improved work of breathing, and improved scrubber function. However, use of anything other than normoxic diluent or diving outside of recreational sport diving limits requires significant additional diver training.

Does the rebreather take a long time to maintain?

Yes and No. Many rebreather sport divers, including Poseidon divers, find they spend noticeably more time on equipment compared to open-circuit because the rebreather diver must always be careful and disciplined about maintenance. If you have been habitually careful with your open-circuit dive equipment and treat your equipment with respect, as an experienced rebreather diver you will spend only slightly more time with your maintenance than you did with open-circuit.

I've heard the Poseidon rebreather Power-On-Self-Test is troublesome, is that true?

The early Discovery MK VI units were annoying about passing the positive pressure test and the sensor validations, but later revisions of the firmware corrected those issues although the reputation persists. In my experience, the Se7en does not have any issues with the POST. However, on rare occasions I do encounter specific individual divers who seem to consistently have problems with failing the POST on their Poseidon unit, especially when they stubbornly refuse to follow best practice and use an assembly checklist. Invariably I find these (often very experienced) rebreather divers were poorly trained on the specifics of the Poseidon model, so the POST really did find a issue they needed to correct before diving. Once you receive proper training, you may expect your unit will easily pass the POST every time.

How well does the Poseidon rebreather travel?

The Poseidon rebreather is very travel friendly. A key design goal was to minimize size/weight and divers are able to travel by air with it as carry-on luggage in most circumstances. Regardless of the brand of rebreather it can be annoying to travel with cylinders because they are carefully examined by security personnel, and occasionally even confiscated. You may prefer to rent cylinders at the destination or ship your cylinders ahead.

How is the Poseidon different from other rebreathers?

All of the major rebreather models are good quality units. There is no perfect rebreather; they all have strengths and weaknesses that make each uniquely more or less suited to your needs. The Poseidon Se7en is a richly featured and proven design with good redundancy from a well established manufacturer. The Poseidon is a European design that favors the sport diver with intentions of continuing on to technical diving. It is an exceptionally automated design that is smaller, lighter and simpler to use than many other rebreathers. It is a robust eCCR choice that will take you as far as you wish to go in general sport and technical diving. As an independent dealer, we stock spares and consumables with online ordering and same day shipping.

Is the Poseidon rebreather safe?

No type of rebreather can be said to be categorically safer than another. No rebreather is foolproof, and the fact remains that compared to open circuit there is a disproportionate number of rebreather fatalities, many of which have been attributed to diver error. The quality of training may be the most significant factor affecting rebreather safety. Your safety while diving is controlled by you, not by your rebreather.

Last Updated: Apr-2022

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