SF2 or REvo rebreathers

[JonnyQuest]

I'm looking to get into the rebreather world and have the hard questions to answer. Which unit do I select? I have narrow the field down to two rebreather units, the SF2 and rEvo. I would like to ask the community their thoughts (constructive please) on the both units.

I do realize that both units are very good and will do their jobs is you take care of them and dive correctly. What I'm looking for in the discussion is the finer details and longer term considerations.

Thanks all,

 

[Capt Jim Wyatt]

Both are good rebreathers- the SF2 is new, relatively. Mares bought rEvo so that company will be around a long time. I have no clue who owns SF2 nor how stable of a company it is.

 

[JohnnyC]

rEvo has some interesting features, dual scrubber, rms system, Shearwater electronics, an interesting cell monitoring paradigm. They have their own set of particular issues.

SF2 was basically an evolution from the SF1, a PSCR much like the RB80. It remains very similar to that design. Basically they've added 3 cell monitoring, changed the counterlung and removed the burping. The SF2 has a single counterlung in the can making it very streamlined, Shearwater electronics, easy disassembly and maintenance. It can be quickly swapped from backmount to sidemount configuration. They have their own set of particular issues.

What type of diving to do you plan on doing? Either may be better suited to your particular type of diving. I chose the SF2.

 

[kensuf]

I dive and teach the SF2 because it has incredible water tolerance. If I screw up and accidentally flood the unit (loose lips, etc), as long as it's not a catastrophic failure (cut hose), I can recover the loop. My flood test involved fully flooding a unit then going on a 2 hour dive without surfacing. The SF2 handled like a champ.

The REvo can not recover from a loop flood.

For the type of diving I do, flood recovery is an important consideration. When I'm 2 miles back in a cave I want every option available to me.

 

[JonnyQuest]

@JohnnyC The type of diving I will be doing is photography diving with no caves. I choosing the rebreather for a few reasons. One is time, second is the quietness, and third is gas cost.

@Kenfuf I do hear that the loop flood is the big difference between the two units. I'm not a tech diver yet, but I could image that at 200 ft with an imaginary ceiling that it could be very important to have that option. My question is, how often does a flood loop happen? is it rare or is it a common thing that most rebreather experience.

To add to the questions for deciding, I have one instructor that wants to become a SF2 instructor and would like to use me as their first student. While I trust this person, I'm curious on thoughts on going with a new instructors. Some time new instructors are more detail then a instructor that has gone over the material a thousand time and skip things.

 

[Capt Jim Wyatt]

The REvo can not recover from a loop flood.

I hear that a lot.

I literally have hundreds of dives and hundreds of hours on rEvos and never one time had a loop flood.

 

[Superlyte27]

I hear that a lot.

I literally have hundreds of dives and hundreds of hours on rEvos and never one time had a loop flood.

I have, 2000' back in a cave when a nut inside the countering came off that fastened to the bulkhead that held the opv.

Out of SF2 or Revo, SF2.... it'll breathe better. But look at liberty also. It's pretty stellar.

 

[The Chairman]

I'm partial to the SF2 and was certified on both.

 

[kensuf]

@Kenfuf I do hear that the loop flood is the big difference between the two units. I'm not a tech diver yet, but I could image that at 200 ft with an imaginary ceiling that it could be very important to have that option. My question is, how often does a flood loop happen? is it rare or is it a common thing that most rebreather experience.

To add to the questions for deciding, I have one instructor that wants to become a SF2 instructor and would like to use me as their first student. While I trust this person, I'm curious on thoughts on going with a new instructors. Some time new instructors are more detail then a instructor that has gone over the material a thousand time and skip things.

Loop floods are rare, but it only takes one. I had a partial flood on a KISS Classic that was 100% caused by a DEU related issue (defective end user, aka me). I was unable to de-water the KISS and still had 3 hours of deco to go before I could surface, the entire time I was wondering when I would need to bail out because the loop was going to become unbreathable.

Thankfully, and even if I did have to bail out, I had enough deco gas to complete deco, but it was enough of an event that for me, the ability to dewater the unit was important.

The SF2 isn't for everyone. It's a great unit for what it does, and there are some amazing pro's, but there are some cons too.

Pro's:

The SF2 is incredibly water tolerant and recovering a flood is a breeze. I don't know if there's another unit on the market that can recover as easily.

The SF2 is a very clean/basic unit. The bellows counter-lung leaves your chest area open without clutter.

The SF2 is a very simple unit to build up and tear down. We're talking minutes for build and tear down.

The SF2 uses a Jaksa solenoid and Shearwater electronics. Batteries are a simple 9v and AA, which can be found anywhere in the world.

Work of breathing is delightful when you're in trim. I always hear from others that the work of breathing on the SF2 is bad, but those people are talking about hydrostatic work of breathing, caused by water pressure. While it's true that if you're diving with your feet facing the ground and your head facing the surface, breathing exhaling into an SF2 is difficult, I personally don't dive with my trim that way so I do not notice this. OTOH, coming from a KISS Classic, I find the resistive work of breathing on the SF2 to be very low and very nice.

The SF2 is a relatively light unit. I've got two packed up to fly down to the Cayman Islands with me for next week and I'm not going to go over my baggage allowance.

Con's:

The placement of the O2 sensors could have been better thought out. The cell faces are "up" when the unit is built up and standing. This means water can bead and pool on the cell faces and throw the readings off. While this isn't a problem while diving, unless you typically dive with your feet pointing straight down, it means you probably want to pull the head off and turn it upside down between dives (or lay the unit down, which may be tough on a boat).

The O2 cells are not the R-22D, which are commonly used in the Prism2, KISS, Optima, Revo, Hammerhead, Poseidon, etc.. Instead the sensors are a more unique package, only used by the SF2. This means you should remember to pack spares if you're traveling, because spares may be impossible to come by.

A stock unit does not come with a HUD and while it does come with a fischer connector, it does not support adding a second CanBus read-only sensor. This means you can't use a CanBus HUD (the JJ hud is the one I'm thinking about). This may not be a big deal to you though.

The stock cylinder attachment brackets are a weak point. A friend of mine has had the misfortune of having his O2 bottle pop off 3 times, once was while we were laying line 1.5 miles back in a cave. I've been thinking about other solutions, and hope to have something soon that solves this problem.

 

[kensuf]

For the diving I like doing, long range cave exploration, the SF2 is a great unit. However, every rebreather has pro's and con's, and there is truly no "this is the best rebreather ever!" unit out there.

Figure out the type of diving you really want a CCR for, then figure out the things that are important considerations for that kind of diving.