Clare
Retired - going diving
We wanted to be able to bail out on to a reasonable volume of gas via the bailout valve. We also wanted to be able to donate via a long hose and this needed a reasonable gas volume too. There can be much debate about long hoses on RBs but this is how we have dived for several years now and far from being a complication, we didn’t like the prospect of diving without one.
Obviously we could use bigger back gas tanks, perhaps manifolded al la the UTD versions. But this meant less flexibility and more complexity with off board O2 on every dive in addition to other stages. There would also be times, as we had already found, that bigger tanks were difficult to get hold of or get to site.
So we needed off board, but with an ability for it to feed not just a BOV or manual add.
We also wanted to be able to access the onboard O2 OC should the RB fail - but did not wish to have a live second stage regulator on it for obvious reasons. I know that others have got round this with flow stops but this was not acceptable to us and we pressed to find a solution.
One of the great things about an RB80 is how flexible it is and how many options you have available to you if things break. We wished to emulate this in the CCR, in a config which would allow us to operate with any size of back gas.
So, bit by bit this came together. I won;t bore you with the concepts which hit the cutting room floor but there were many as it got redesigned and simplified. With help from RB world users (mostly who told me what we shouldn’t do
), and the star of the show, Neil Brock from Bristol Channel Diving who grabbed this when we came to him late on and ran with it - producing a working model which could be tested.
We have stolen various ideas from many people, NickB and Mark Davies both, a well as Richie. However, coming at it afresh and in the advantageous position that we saw the good and bad of everyone’s solutions, meant we could cherry pick and refine.
So, forgive me if any part of my explanation is not clear as I have never done this before, and feel free to ask questions. The unit in the picture is Rob Dobson's (or what is left of it) and therefore has a Dil MAV fitment by the ADV - ignore this.
The unit is rigged in this picture with 7 litre tanks. The regs will work with any size of tank in this orientation, from 3s to 12s - and probably bigger although I won’t work at that stage
The backplate is a standard halcyon ali plate and harness. With 300 bar 7s I don’t need any weight in the frame or anywhere else which is nice. For 3s I would move to a 5mm plate. There are no trim issues with either.
The right post is O2 and the regs feed the normal config of pressure gauge (clipped to D ring on light canister), solanoid and manual add.
The manual add has been replaced with a CEJN nipple. The nipple is flow restricted but is compatible with a full flow CEJN female - the need for which will become clear in a minute.
The left post is Diluent. The feeds coming of this are to the pressure gauge clipped to waist D ring as normal, wing and switchblock.
The switchblock (a glorifed name for what we ended up with) is what took the time.
This accepts a pluggable feed from back gas or from a stage. It in turn feeds the BOV, the ADV and the long hose via the 3 way connector from whatever is plugged in. Thus a dive on 3 liter cylinders with an 80 for bailout will have the unit and all bailout gas including long hose attached to the off board. If off board has to be handed off then backgas can be replugged.
Routing took some time and effort. We manged to get it that the 3 way sits under the loop at the top of the unit in a place where, when the wing is inflated would be well protected. n this photo I have pulled the wing down to get a clear view of the routing.
On the switchblock one way check valves prevent gas from escaping via unplugged connections. The connections are large bore CEJN connectors which deliver sufficient quantity of gas for someone working hard (or subject to CO2 issues) at depth.
Neil tested the system with gas (air) on a pair of well adjusted and recently serviced Scubapro Mk25s, using the optimum end port for the best flow characteristics, and the system worked fine.
Typically, a well set up Mk25 will flow approximately 790 - 800 LPM on the surface with an I.P. of 9 bar. The system gave the following:
From off board supply to 3 way manifold - 810 LPM
From on board supply to 3 way manifold - 780 LPM
The slight difference in flow rates is we suspect, down to the slightly more convoluted path of gas from on board to JJ.
If the RB fails then bailout can be via BOV or longhose. This has the added advantage that mouthpiece loss which would prevent the use of the BOV would not get in the way of accessing on board gas.
If the Diluent is hypoxic then off board breathable gas (deep deco gas) can be put through the block and on board disconnected. This would then be available through ADV, BOV and longhose. No more shallow hypoxic problems.
If RB has failed, the onboard O2 can be accessed via the switchblock - again to longhose or BOV. The CEJN connector to the O2 MAV unplugs and connects to the off board feed to the switchblock. It’s a slight pita to line up but you wouldn’t want such a radical move to be easy - it would have to be a definite decision.
Loss of Dil is not normally a problem in the sea where direct ascent can be made, but in a cave where descent may be a necessary part of exit this is handy to have. The feed from on board Diluent can also be connected directly to the O2 MAV should the switchblock fail. In a complete loss of onboard dil, off board dil can still be used directly if routing unaffected by issue or via O2 MAV. Buddies gases can be utilised in the same way and their long hose can (with an adaptor we would carry only on a long dive) also push gas through both sides of the unit. This is a fix we took from the cheaters cheaters we carried on the RB80. It would be a convoluted fix and should never be a first line of defence but with a long enough dive it is kinda nice to have available.
The unit can take off board dil and off board o2 - so dives in those hard to reach/hard to fill places are fine. With only the wing being fed from Diluent when off board is being used the cylinders stay reasonably full which makes logistics slightly easier - especially when dealing with smaller bottles.
In the event of a CO2 hit the diver can be managed through stages switches without ever having to come off the loop.
Bigger back gas allows for less bailout on shallow dives, onboard O2 accessible OC allows for more efficient deco OC with fewer stages.
We've run this past a few JJ divers now and had positive feedback. I really am interested in other feedback especially if you think we've missed something. Of course some people will have different views on our set up, particularly the long hose and the orientation of the cylinders but this was to fit a niche and build on our previous experience - it is not the first step of a new DIR rebreather movement so you don't have to do it too
Obviously we could use bigger back gas tanks, perhaps manifolded al la the UTD versions. But this meant less flexibility and more complexity with off board O2 on every dive in addition to other stages. There would also be times, as we had already found, that bigger tanks were difficult to get hold of or get to site.
So we needed off board, but with an ability for it to feed not just a BOV or manual add.
We also wanted to be able to access the onboard O2 OC should the RB fail - but did not wish to have a live second stage regulator on it for obvious reasons. I know that others have got round this with flow stops but this was not acceptable to us and we pressed to find a solution.
One of the great things about an RB80 is how flexible it is and how many options you have available to you if things break. We wished to emulate this in the CCR, in a config which would allow us to operate with any size of back gas.
So, bit by bit this came together. I won;t bore you with the concepts which hit the cutting room floor but there were many as it got redesigned and simplified. With help from RB world users (mostly who told me what we shouldn’t do
), and the star of the show, Neil Brock from Bristol Channel Diving who grabbed this when we came to him late on and ran with it - producing a working model which could be tested.We have stolen various ideas from many people, NickB and Mark Davies both, a well as Richie. However, coming at it afresh and in the advantageous position that we saw the good and bad of everyone’s solutions, meant we could cherry pick and refine.
So, forgive me if any part of my explanation is not clear as I have never done this before, and feel free to ask questions. The unit in the picture is Rob Dobson's (or what is left of it) and therefore has a Dil MAV fitment by the ADV - ignore this.
The unit is rigged in this picture with 7 litre tanks. The regs will work with any size of tank in this orientation, from 3s to 12s - and probably bigger although I won’t work at that stage
The backplate is a standard halcyon ali plate and harness. With 300 bar 7s I don’t need any weight in the frame or anywhere else which is nice. For 3s I would move to a 5mm plate. There are no trim issues with either.
The right post is O2 and the regs feed the normal config of pressure gauge (clipped to D ring on light canister), solanoid and manual add.
The manual add has been replaced with a CEJN nipple. The nipple is flow restricted but is compatible with a full flow CEJN female - the need for which will become clear in a minute.
The left post is Diluent. The feeds coming of this are to the pressure gauge clipped to waist D ring as normal, wing and switchblock.
The switchblock (a glorifed name for what we ended up with) is what took the time.
This accepts a pluggable feed from back gas or from a stage. It in turn feeds the BOV, the ADV and the long hose via the 3 way connector from whatever is plugged in. Thus a dive on 3 liter cylinders with an 80 for bailout will have the unit and all bailout gas including long hose attached to the off board. If off board has to be handed off then backgas can be replugged.
Routing took some time and effort. We manged to get it that the 3 way sits under the loop at the top of the unit in a place where, when the wing is inflated would be well protected. n this photo I have pulled the wing down to get a clear view of the routing.
On the switchblock one way check valves prevent gas from escaping via unplugged connections. The connections are large bore CEJN connectors which deliver sufficient quantity of gas for someone working hard (or subject to CO2 issues) at depth.
Neil tested the system with gas (air) on a pair of well adjusted and recently serviced Scubapro Mk25s, using the optimum end port for the best flow characteristics, and the system worked fine.
Typically, a well set up Mk25 will flow approximately 790 - 800 LPM on the surface with an I.P. of 9 bar. The system gave the following:
From off board supply to 3 way manifold - 810 LPM
From on board supply to 3 way manifold - 780 LPM
The slight difference in flow rates is we suspect, down to the slightly more convoluted path of gas from on board to JJ.
If the RB fails then bailout can be via BOV or longhose. This has the added advantage that mouthpiece loss which would prevent the use of the BOV would not get in the way of accessing on board gas.
If the Diluent is hypoxic then off board breathable gas (deep deco gas) can be put through the block and on board disconnected. This would then be available through ADV, BOV and longhose. No more shallow hypoxic problems.
If RB has failed, the onboard O2 can be accessed via the switchblock - again to longhose or BOV. The CEJN connector to the O2 MAV unplugs and connects to the off board feed to the switchblock. It’s a slight pita to line up but you wouldn’t want such a radical move to be easy - it would have to be a definite decision.
Loss of Dil is not normally a problem in the sea where direct ascent can be made, but in a cave where descent may be a necessary part of exit this is handy to have. The feed from on board Diluent can also be connected directly to the O2 MAV should the switchblock fail. In a complete loss of onboard dil, off board dil can still be used directly if routing unaffected by issue or via O2 MAV. Buddies gases can be utilised in the same way and their long hose can (with an adaptor we would carry only on a long dive) also push gas through both sides of the unit. This is a fix we took from the cheaters cheaters we carried on the RB80. It would be a convoluted fix and should never be a first line of defence but with a long enough dive it is kinda nice to have available.
The unit can take off board dil and off board o2 - so dives in those hard to reach/hard to fill places are fine. With only the wing being fed from Diluent when off board is being used the cylinders stay reasonably full which makes logistics slightly easier - especially when dealing with smaller bottles.
In the event of a CO2 hit the diver can be managed through stages switches without ever having to come off the loop.
Bigger back gas allows for less bailout on shallow dives, onboard O2 accessible OC allows for more efficient deco OC with fewer stages.
We've run this past a few JJ divers now and had positive feedback. I really am interested in other feedback especially if you think we've missed something. Of course some people will have different views on our set up, particularly the long hose and the orientation of the cylinders but this was to fit a niche and build on our previous experience - it is not the first step of a new DIR rebreather movement so you don't have to do it too
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