Fathom CCR vs JJ-CCR

[rjack321]

Only having dove a 2.7 Meg eCCR I am not getting the solenoid buoyancy issue. If put in a SP of 1.2 it just stays there. I use up 150mL of O2, the SP drops a tiny bit, the solenoid puts it back with way more precision than I could do with the MAV.

Yes if I go up 8ft the ppO2 drops, the solenoid adds, and I am buoyant by not only the expansion of my 3 gas spaces (suit, wing, CLs) but by the O2 addition. But I have to vent something anyway (usually CLs for only going up 8ft) so that fixes my buoyancy despite the O2 addition. I'm not understanding "the solenoid screws up my buoyancy" problem.

 

[taimen]

Only if you block the 1st stage.
I think people diving with unblocked 1sts with a needle valve are nuts. I tried it and almost killed myself. The flow changes crazy fast with relatively minor depth changes and you need to almost constantly figit with the needle setting.

How would you build a hybrid JJ (or meg)?
I have seen some people double their oxygen, with one cylinder/1st feeding the solenoid and another connected to MAV. Would it make sense to have a doubled oxygen with one US4 feeding solenoid and a blocked DS4 for needle valve/MAV.

Yes if I go up 8ft the ppO2 drops, the solenoid adds, and I am buoyant by not only the expansion of my 3 gas spaces (suit, wing, CLs) but by the O2 addition. But I have to vent something anyway (usually CLs for only going up 8ft) so that fixes my buoyancy despite the O2 addition. I'm not understanding "the solenoid screws up my buoyancy" problem.

I fully agree with this. I am just thinking about the hybrid system since it was brought up in this thread.

 

[doctormike]

I'm a photographer with a big DSLR and dual strobes. I virtually never dive without it. Macro, wide angle, video. I have never felt that my rebreather was causing a problem with that...

 

[rjack321]

How would you build a hybrid JJ (or meg)?
I have seen some people double their oxygen, with one cylinder/1st feeding the solenoid and another connected to MAV. Would it make sense to have a doubled oxygen with one US4 feeding solenoid and a blocked DS4 for needle valve/MAV.

Leon actually made or makes a hybrid kit for the 2.7 Meg. I don't know if it fits later models. The orifice is in the head right next to the solenoid so you just block the 1st stage and poof hybrid. Leon thinks hybrids are the worst of both worlds though and might argue with you about buying a conversion kit. He's not big on mCCR either even though he used to make one.

If you didn't want to use his kit, the easiest approach is to drill and tap a hole into whichever T piece you want to have the constant mass go in. Then run a 2nd O2 hose through a orifice holder from Martin / TecMe or up to a needle then to the T piece.

 

[doctormike]

Leon actually made or makes a hybrid kit for the 2.7 Meg. I don't know if it fits later models. The orifice is in the head right next to the solenoid so you just block the 1st stage and poof hybrid. Leon thinks hybrids are the worst of both worlds though and might argue with you about buying a conversion kit. He's not big on mCCR either even though he used to make one.

If you didn't want to use his kit, the easiest approach is to drill and tap a hole into whichever T piece you want to have the constant mass go in. Then run a 2nd O2 hose through a orifice holder from Martin / TecMe or up to a needle then to the T piece.

Can you just replace the MAV button on a Meg with the needle like people say you can on a JJ? Or do you need to drill a hole in the loop?

 

[rjack321]

Can you just replace the MAV button on a Meg with the needle like people say you can on a JJ? Or do you need to drill a hole in the loop?

The Meg O2 MAV is a drysuit inflator on the CL, so no. You need to tap into a T piece or put the orifice in the head parallel with the solenoid.

 

[tbone1004]

Can you just replace the MAV button on a Meg with the needle like people say you can on a JJ? Or do you need to drill a hole in the loop?

if you have BMCL's then yes, but like @rjack321 said the normal configuration uses a drysuit inflator for the MAV so you would have to tap into the T-piece or the head. Neither of which is particularly difficult to do. That applies to any rig with that uses drysuit style inflators for the mav's. Anything that has a button MAV like the ones listed below would just need it swapped out with the needle valve. The Revo's triple MAV won't work though since it handles Dil and O2 in the same monstrous block.

Commonly seen on the Hammerheads, XCCR, etc etc

Often seen on the O2ptimas

The JJ's

 

[rjack321]

So the JJ or the X units would be better suited to needle hybridizing than a Meg. There are free inlet ports in my Meg head if I was interested in hybridizing mine but I don't have any interest

 

[rsingler]

Leon thinks hybrids are the worst of both worlds though...

Care to speculate?

 

[tbone1004]

So the JJ or the X units would be better suited to needle hybridizing than a Meg. There are free inlet ports in my Meg head if I was interested in hybridizing mine but I don't have any interest

anything with bmcl's, yeah. I wouldn't buy a new meg these days though, company seems super janky. Hell, their website still doesn't even have the Tiburon or Minnow lungs on there, and it still has the Meg15 and Pathfinder which have been discontinued.
While it is a damned good rebreather, it's not one that I would recommend anyone even remotely consider buying new

@rsingler Leon has lots of opinions, many of them quite controversial including the addition of O2 on the inhale side of the loop. The backwards loop direction I don't necessarily disagree with since it is the same flow direction as the double hose regulators, but to have the O2 on the inhale side is very strange. I don't disagree with a CMF hybrid being the worst of both worlds though. You add the complexity of a solenoid but never really use it, and you add all of the annoying factors of a CMF which is the blocked first stage *just annoying to begin with, but also depth limiting*, and very high risk of the CMF itself becoming clogged. He hasn't done anything with a needle valve which does remove the two weird bits of a mCCR, and I highly doubt he will.