UTD MX System mCCR Rebreathers

Introduction

10 Covenants of UTD

Background & Design Philosophy

Ultimately we keep the diving and training philosophy of UTD and incorporate the skill set from UTD open circuit diving. This makes it consistent with previous training, philosophy, skill set and ultimately compatible with other UTD/DIR mCCR rebreathers divers, along with other UTD/DIR Semi Closed Rebreather divers UTD/DIR Open Circuit back-mount divers and UTD Z Side-mount divers.

The way we configure our system, is to use standardized bottom mixes as bailout and dil and at max depth this has a PPO2 of 1.2. Therefore small additions of backgas/dilute can be added while on the bottom to compensate for loop PPO2 volume drop (see class tests) instead of O2 or diver loop volume error (leaking mask). By adding Diluent on the bottom this reduces risk of O2 issues at depth dramatically. A traditional "dilflush" can easily be done to keep the loop PPO2 at the desired PPO2. By eliminating this constant bleeding of O2 in to the system, it is much easier to manage the system and reduces our risk of O2 spikes. Essentially, we need to add very little to no O2 at max diving depth to compensate for PPO2 drop, as the Diluent we add is generally above 1.0. On a typical dive the changes in depth and inconsistencies in the diver interface (clearing a mask) requires that the diver add additional gas to the loop. That gas is generally Diluent which is within the correct PPO2 range (at max depth) therefore requiring very little O2 addition.

The argument that the COPIS or leaky valve is safer as it is a "safety net" is truly invalid in our opinion as this so called "Safety Net" is can never accurately predict you O2 needs and therefore by definition it is really not a "safety net" but a false sense of security.

The beauty and design of the MX series configuration is just how well each component is thought out. Each and every piece of equipment has a purpose (if not two), place and backup. For example, if you O2 injector was to fail closed, you would simply plug the O2 into the diluent injector. Or if you were to lose your right post and could not add diluent via the injector, you can simply add diluent from the BOV. All aspects and bailout modes have being deliberately thought out to be holistic, consistent and compatible, down to the reason we wear standardized UTD/DIR mixes on our back or side (bailout/diluent) and deco bottles in standard OC UTD/DIR configuration. This is important because it serves a dual purpose: Number 1, if the PPO2 handsets or O2 sensors are faulty, wet or damaged and the electronics system have failed, the MX Series can easily be used in an identical fashion to the UTD/DIR PSCR’s or Passive Semi Closed Circuit Rebreathers manner (See Class Tests.) It will extend your bailout backgas and deco gases to an 8 to 1 ratio while exiting in that emergency. Number 2. If the rebreather is flooded or unusable, one could just simply bailout to full Open Circuit and go home. So the backgas and deco gases serve us to do PSCR or OC bailout if needed. As I said every piece of equipment has a purpose , place and backup.

Diving Mixed Teams

The first rebreather to be introduced to the DIR community was the Halcyon pSCR Rebreather, which we affectionately termed "the fridge,” and then later, around 2001, we started using the pSCR - RB80. Now, almost a decade later, we have moved to fully closed circuit systems or mCCR (manual closed circuit rebreather) which we called the MX Series. These units can be configured into a Back-mount system (CO2 Canister, Head and Diluent tanks mount on your back) or a S-de-Mount System (CO2 Canister, Head and Diluent tanks mount on your side.)

But regardless of which unit we dive, we have stuck to the core principles of UTD/DIR-consistency within the team (and community) of bailout volume and logistics, standardized gases for bottom gas and deco, Ratio Decompression strategies, matched equipment configuration, skill procedures for out-of-gas and valve failures, and so on.

The MX back-mount rebreather configuration is simply a classic DIR/UTD technical configuration (a set of doubles and deco bottles as needed) wrapped around the rebreather which syphons off a tiny amount of the OC gas for use in the CCR but leaves the majority of the OC gas for bailout. The MX side-mount rebreather configuration is the UTD Z-Side-Mount system in a technical configuration with the rebreather and diluent tanks mounted on the side of the diver. The rebreather syphons off a tiny amount of the OC gas for use in the CCR but leaves the majority of the OC gas for bailout.

Keep in mind that in all cases we add gas (either O2, deco or Dil) manually - there is nothing on the system that adds any gas without you wanting to. Meaning there is no solenoid, no electronics or other things that could unintentionally add gas without your knowledge. It is simply a CO2 canister, counter lung, breather loop and so on with O2 sensors to measure the PPO2. The CCR can be turned into a PSCR quickly and easily (see Class Tests) if needed, so PSCR becomes a bailout mode to the mCCR, if the electronics fail, and the OC becomes a bailout to the CCR/PSCR if the units is completed flooded.

As a side note: UTD does require an O2 sensor on all rebreather configurations including any traditional pSCR system such as the RB80 or RB2000 and others.

So here are a few things that are important for an OC buddy when diving in the mixed team with pscr and/or a mccr diver. These apply specifically when diving with a diver using the MX back-mount or side-mount systems :

1. It's important that a RB diver is always moving around slightly so you know they are alive, as there won't be bubbles to confirm breathing.

2. In emergencies, such as CO2 hits, valve failures or out of gas situations, the RB diver immediately bails out from the CC to OC by simply flipping the BOV to open circuit. This happens by moving the lever on the bailout valve to the OC position, which opens the "necklace" regulator on the bail out valve (BOV). Now the bailed out RB diver is on the backup reg on the left post in Back-Mount or the Z-Manifold if on Side-mount, just like a the standard systems, and both divers in a mixed team are now on open circuit. The backgas is a UTD standard gas and is always breathable at any point in the dive. This bailout procedure eliminates the need for the CC diver to monitor the rebreather while dealing with the emergency. The CC diver can now give full and undivided attention to the emergency. As we carry ample bailout this is not considered problematic from a gas management perspective and because the bailout valve is simple and easy to access it and will be easy to return to CC once the emergency is dealt with. We propagate the message of "when in doubt, bailout."

A side tangent : The message propagated in other circles of the ccr diving world of staying on the rebreather at all costs while dealing with an emergency is massively problematic, as the CC diver can potentially stop monitoring the rebreather while dealing with the emergency and therefore may create a very dangerous situation. Even if the electronics are only there as a backup they too could fail as they are not in use at all times.

The reason this message of staying on the CC while dealing with emergencies was propagated is because number one, many ccr divers do not personally carry sufficient bailout volumes to handle an emergency in OC mode (they try to divide the bailout for one person between team members or just simply go alpinists style - no bailout at all) and secondly because their bailout configuration is so massively convoluted and/or difficult to donate or restore to it's original state that once deployed and the emergency is dealt with, returning to CC can be a massive pain in the butt, so they simply just try to stay on the unit while dealing with the emergency.

An example I have seen is carrying the bailout in a stage bottle which forces one to select a bottle, pull the regulator from the stage bottle bungee, remember to turn it on and then bailout to deal with the emergency, then once dealt with try to return the regulator to it's original position. It reminds me of the "pre" DIR days when we would stuff the long hose into a bungee and would have to pull it out of the bungee to donate, then it was such a hassle to return to the bungee. So we would not bother practicing s-drills because it was too much trouble to put the long hose away. Hence the Hogarthian system was born to simply wrap the long hose back around your neck, which has now become the standard method of UTD/DIR long-hose configuration.

But, back to mixed teams: 3. If an OC teammate needs gas, the CC diver switches to OC by moving the lever on the bailout valve, unclips the long hose, lifts the loop out of the way, donates the long hose, and stays on OPEN CIRCUIT. Now both divers are on OC, problems can be sorted out, then the RB diver can go back to CC. We put the CC diver on open circuit during an emergency so there is no need to manage the rebreather and the PPO2.

4. If an OOG diver grabs the regulator off the O2 bottle in an emergency, the regulator has an isolator at the second stage, so essentially the gun is not loaded- although the bottle is on and feeding the RB, the second stage is off, so it takes two steps to breathe pure O2. There's an overpressure relief valve on the O2 first stage so the second stage can be isolated safely. At recreational depths, there often won't be a second stage on the O2 bottle, since the only time it would be used is for emergency O2 deco.

5. Cautions that OC divers in a mixed team should know about
Prevent the system from flooding by not taking the loop out of the mouth unless the BOV is set for open circuit. Floods make the rig heavy, but the wing should provide enough lift to bring the diver to the surface in neutral buoyancy. A small amount of water in the loop can easily be cleared.

PPO2: There is a handset and a head-ups display. The primary handset is attached to the divers right arm or clipped to the hip d-rings of the diver. The back-up is the heads up display (HUD) and is mounted in plain-view of the diver. The handset displays the individual PPO2's from each of the three sensors on the main-screen. The handset and the Heads up display (HUD) are independent of the other, so if the primary or secondary were to fail you would have the other - back-up.

With the Shearwater HUD, we tried to find the best of all worlds. It displays the PPO2 only, which makes it a redundant PPO2 meter. Since it uses three LED’s simultaneously, it can display them quickly. A typical 1.3 takes about 2 seconds to read. After a few dives, many divers have said that they do not need to consciously “read” the displays; they look at the display and their brain recognizes the number of flashes.

When there is a problem with a sensor, it is noticeable immediately as one of the LCD’s flashes different from the others. As the diver knows what to expect, when something different happens it really jumps out at them.

The Shearwater HUD does not display continuously; there is usually 5 seconds between the displays. Also, as the PPO2 gets farther from 1.0, the light DENSITY gets higher. If you are more than 0.50 away from 1.00, the power is turned up to the high intensity LED’s; so they get brighter! At 0.20 you have three very bright red LED’s flashing just about continuously in the corner of your eye.

MX-Z mCCR Rebreather Side-mount/Back-Mount Rebreather in details

- Back-Mount Focused:

MX-Z mCCR Rebreather Side-mount/Back-Mount Rebreather Intro

- Side-Mount Focused:

Some older MX Rebreather Configuration information:

The A to Z of UTD’s MX-Z Side/Back-mount mCCR Rebreather

MX-Z Side/Back-Mount Configuration

A. Diluent Supply & Bailout Gas.
B. Axial CO2 Canister - Side/Back-Mount
C. Side-Mount Attachment
D. Dil/Bailout plugs into Z-System Manifold
E. Off-board O2 and/or Bailout Deco Tank
F. CCR Loop w/ built in water trap
G. Bailout Open Circuit Valve or BOV
H. Left-Side O2 Injection block and Inlet with female QC6
I. Back Mounted Counter Lungs - Inhalation/Exhalation(Left/Right)
J. Over Pressure Valve (OPV)/ Water Dump on the Exhalation Counter lung
K. Diluent gas addition block with female QC6
L. Adjustable Position Heads Up Display (HUD)
M. Primary PPO2 Monitoring system with OLED Handset mounted on a Fischer.
N. Secondary PPO2 Monitoring system is a Heads Up Display or HUD
O. Open Circuit Bailout on a 7ft/2m Long Hose for donating to Buddy.
P. Isolator Shutoff for the Diluent Feed
Q. O2 feeds into right side 90 degree T (exhalation counter lung)
R. KISS Head and 3 x O2 sensors
S. Diluent feeds into left side 90 degree T (inhalation side)
T. BOV/OC 2nd stage feed - Connected to Z-Manifold (Distribution Block)
U. Z-Manifold (distribution block) mounted to Z-Harness
V. SPG for Diluent/Bailout
W. SPG for O2 Supply/Bailout Deco
X. Over Pressure for O2 first stage
Y. Side-Mount Attachment Bungee
Z. Standard Z-System harness and Z-Plus Trim/wing

The A to Z of UTD’s MX HH/KISS Back-mount mCCR Rebreather

A. Manifolded Diluent Supply & Bailout Back Gas.
B. Right Post
C. Left Post
D. Exploration Manifold w/ Isolator
E. Off-board O2 and/or Bailout Deco Tank
F. CCR Loop w/ built in water trap
G. Bailout Open Circuit Valve or BOV
H. O2 Injection block and Inlet with female QC6
I. Split Back Mounted Counter Lungs -Inhalation/Exhalation(Left/Right)
J. Over Pressure Valve (OPV) on the Exhalation Counter lung
K. Diluent gas addition block with female QC6
L. Adjustable position Heads Up Display (HUD)
M. Primary PPO2 Monitoring system with LCD Handset.
N. Secondary PPO2 Monitoring system with LCD Handset
O. Open Circuit Bailout on a 7ft/2m Long Hose for donating to Buddy.
P. Isolator Shutoff for the Diluent Feed
Q. O2 second stage regulator Isolator shutoff
R. Head and O2 sensors
S. Diluent feed - Connected to right post
T. BOV/OC 2nd stage feed - Connected to the Left post
U. C0-Axial (Kiss) or Radial (HH) CO2 cartridge, spacer/water trap and Canister
V. SPG for Diluent/Bailout backgas
W. SPG for O2 Supply/Bailout Deco
X. Over Pressure for O2 first stage
Y. Exploration tank bands
Z. Standard UTD/DIR backplate, harness and wing

MX Kiss Rebreather Configuration

Here are some images from the MX KISS Rebreather configuration.