Why? There seem to be very few pre-owned mCCRs on the market. Isn't that because people are quite happy with them? In what way do people outgrow them?
I often see used mCCRs (rEvo and KISS) on the market. Just need to know where to look; I see a lot on CCRexplorers and RebreatherWorld or on Facebook. At least on the rEvo side, I see a lot of people selling their mCCRs to upgrade to a hCCR or a newer model but honestly I think it's usually a while before people "outgrow" them. You're WAY more likely to outgrow a SCR than a mCCR. I don't see the point in buying one; If you can afford an SCR then you can afford a mCCR.
In my opinion (arguably limited since I only just broke 100 hours on my unit), starting off with a mCCR is a good choice. You learn to fly the unit manually without a solenoid simply by the virtue of not having one to begin with
mCCRs are arguably simple, easy to repair and understand. In theory, learning on mCCR gives you discipline for when **** hits the fan and you are on a eCCR.
On a rEvo mCCR the "depth limit" is 80m / 260ft. If you're just starting on a rebreather you have a whole world to grow before you start doing 300ft dives on a unit.
An example of how you can "outgrow" a mCCR..
A traditional mCCR which uses constant mass flow (CMF) principal with a fixed orifice typically has a depth limitation based on the IP of the first stage on the Oxygen regulator. Basically, regulators on oxygen side of a mCCR are modified to be fixed so that they do not compensate or adjust IP as depth increases.
You can get by this "limitation" by plumbing offboard gas into your unit once your reach this stage in your rebreather diving. I suppose at this point is where a eCCR may make more sense since it does not have the a true depth limitation.
Here are a couple good articles by Paul Raymeakers (maker of rEvo) and Dr. Mel Clark (Popular rebreather instructor)
Copis Megalodon MCCR ADVANCED DIVER MAGAZINE by Mel Clark
Understanding Constant Mass Flow ADVANCED DIVER MAGAZINE By Paul Raymaekers
Mel Clark:
But by preventing the regulator from compensating as depth increases, the regulator will no longer allow oxygen flow nor will the diver be able to manually add oxygen at the depth that is the same as the interstage pressure (IP)
Paul Raymeakers:
Now what does this mean when we dive a rebreather with an absolute pressure regulator (so that we can use an orifice that delivers us a constant mass flow of oxygen over a range of depths): It means that the maximum operation depth of the rebreather is limited to the depth, where the IP equals the pressure in the water. Because at that depth or deeper, no oxygen can be added to the system, as also the manual add valves (MAV) will not provide flow when activated.
In the normal rEvo setup, the IP is set at +/- 11 bars absolute (10 bars overpressure) and the flow at surface is +/- 0.8l/min. At a depth of 100m, the water pressure equals the IP, so the maximum recommended working depth of the rEvo in mCCR of hCCR mode is 80m.
I'd steer clear of a dolphin. Ask 10 people which rebreather and you'll get 11 different opinions. What's your budget? Where do you see your diving at in 3 years?
This is especially true. There are a bunch of fundamental questions you want to ask yourself before purchasing a unit. Most people are very partial to their own unit. In other words, anyone who spends a lot of money on a rebreather is going to try to justify their purchase
There is no perfect rebreather and there never will be.
Just a few off top of my heads,
Back mounted or Front mounted Counter Lungs (things like work of breathing and flood tolerance come into play here)
BOV or no? (can be added later but do you want one stock?)
Axial or Radial Scrubber Design (Prepacked cartidriges or fill your own sorb)
mCCR / hCCR or true eCCR
Shearwater Electronics or something else?
