Poseidon MKVI Rebreather


Since its release in 2012, the Poseidon Discovery MKVI rebreather has caused excitement and confusion within both the dive industry and larger community. We’ve put this information page up to help shed some light on the machine, its ethos, and what’s coming up next.

The first of a new breed of closed-circuit rebreathers termed as “recreational”, the MKVI is designed primarily as an easy to operate unit. It aims to keep things simple across all aspect of CCR diving, including assembly, in water operation and logistics. To qualify “simple”, let’s take a look at some of the features that make the MVKI unique:

  • Pre-packed CO2 Cartridge – putting a rebreather together successfully is nothing to sneeze at; here are lots of opportunities to get it wrong. The MKVI addresses this in several ways, but one of the most significant of these is the pre-packed CO2 cartridge. Although more expensive than the packable variety more commonly found in other units, they eliminate the packing errors and speed up the assembly process.
  • Pre-dive Automated Tests – before a dive can be conducted, the MKVI runs a series of largely automated tests that must pass successfully. If done correctly this process takes about two minutes. In contrast, a typical rebreather requires the operator to manually execute and evaluate the success/failure of each test before getting in the water. In practice, the automated tests are easy to execute and do increase safety, though if the operator is unpractised/unskilled in setting up the unit, they can fail and be problematic for the operator.
  • Bailout Strategy – one of the more complex things about rebreather diving is what to do when things go wrong. Typically this doesn’t happen often, so divers can be unprepared to deal with the complexities of a typical CCR. The response to all failure modes on the MKVI is to bail-out, which with the BOV fitted as standard is simply a matter of flicking a lever, going to OC mode and ascending.
  • Oxygen Cell Validation – unlike most units, the MKVI only uses two oxygen cells. One cells is used to measure the oxygen level, and a second is used to validate the first with a known gas. The approach is unique within the industry and addresses many of the human and electronic dependencies that three cell voting logic has. The process was literally designed by a rocket scientist, Dr Bill Stone.
  • Limitations – the MKVI is electronically depth and time limited to ensure the operator does not exceed their certification level. It does not shut down if you exceed these limits, but it does go into an alarm state until you ascend to a shallower depth (it’s quite annoying). In order to increase or remove these limits, additional batteries modules must be purchased once appropriate training has been undertaken.

Some frequently asked questions we get asked about the MKVI include:

Q. Is the MKVI a real fully closed-circuit rebreather?

A. Yes. It is a fully closed-circuit rebreather with an electronic PPO2 setpoint monitoring system (i.e. eCCR).

Q. Is the MKVI dummy proof?

A. Definitely not! The MKVI is an eCCR that requires commitment and attention from the operator dive safely.

Q. How long can I stay down with the MKVI?

A. The recommended limit for a single dive is 3 hours, based on oxygen and scrubber limits.

Q. How deep can I go with the MKVI?

A. The MKVI ships with an Air Diluent 40m No Deco battery which limits the depth to 40m. Subsequent upgrades exist that take the unit to 40m Planned Deco on air, 45m Planned Deco on Trimix and 60m Planned Deco on Trimix. The latter also requires older units to have a head and counterlung upgrade.

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