SCRs ...whats the point?

magentaseas

Hi
With whats been said in replies to my query (thanks again guys) about getting a SCR, Im now wondering....
What s the point in SCRs in the first place? Or is it just the introduction of the Sport Kiss thats making them a bit redundant?

Sharon

schford

SCR's main advantage is as a gas extender. Well thats what I think any way!

Stuart

Andy M

They are a cheaper version of a real CCR because no electronics are required in a SCR. However the Sport KISS has driven the price point differentiating between SCR and CCR down firmly into SCR territory. The dolphin, ray, etc are all now redundant

On the other side, you do need to be a bit more careful with a CCR, because of an increased risk of hypoxia, hyperoxia, hypercapnia etc.

schford

Hi Andy,

IMHO with an SCR you are just as likely of getting hypercapnia (it uses a scrubber!) more likely to get hypoxia via overbreathing it at shallow depths (often SCRs have no O2 monitoring), and agreed less likey to get hyperoxia!

Stuart

Dave1w

Well I bought a Ray coz it came to around 500 quid all in brand new. So really, I thought why not?
It's something to play with, and it'll be a long time before any CCRs can be had for even twice that brand new.

Dave

EBT

Pros;

Less to go wrong
Easier to setup (generally)
Get more duration out of your lime
Can be run without PO2 monitors (more advisable with some designs than others)
Dont need HP O2.
Cheaper (or certainly should be!!)
Can be small and lightweight.

Cons;

Not bubble free.
To get deco efficiencies, needs multiple drive gases
Not as gas efficient (tend to max out around 10:1)

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wedivebc

I think hyperoxia is the only one less likely on a SCR

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caveseeker7

The first rebreather were pure oxygen rebreathers used in mining and tunneling.
Those were adapted for use UW early on.

Due to the depths limits of pure oxygen (causing hyperoxia = oxygen poisening) O2 was mixed with air to allow for greater depths. Several SCRs were successfully sold for military use in the 50s. The MK6 SCR was long the mainstay for the US NAVY, well until after Biomarine introduced the CCR1000 and its military version , the MK15. The CCR1000 came to the market in 1969, and was build by several companies under various names. I wrote an article on one of those, Innerspace's Porpoise Pack One from the 70s, which back then retailed for around $30,000 with accessories.

Later CCRs like the MK15.5, UT240 and MK-5p that sold to civilains in the 90s were all between $14,000 and $18,000.

So when Dräger introduced the Dolphin's predecessor in 95 to the recreational market for a few thousand dollars it was a big step forward. They had been building military O2 and semi-closed rebreathers for decades.

The Ray followed in hopes to have a smaller, less expensive and easier to use unit that appealed to resorts.

The Azi is a civilian version of a military rebreather.

The Submatix is just another try keep that market going, and the general layout, case, etc, is "inspired" some of Drägers military SCRs (many of which found their way into civilian hands once the military dumped them).

The RMV keyed system isn't new, either, and offers several advantages over the cmf SCRs above. More consistant fO2 in the loop and increased gas conservation.

None of them needs electronics or power to operate, which appeals to some people, although as pointed out before, O2 monitoring is a rather good idea.

CCRs didn't get affordable until the Inspiration, and that's still a relative term.

The KISS rebreathers did change the equation a bit, by costing less than electronically controlled rebreathers and using O2 monitors as the only electronics.
The idea isn't new, either, but was marketed successfully for the first time.

There are some who argue that the KISS rebreathers aren't really CCRs, rather SCR that usually don't expell gas.
The manual gas addition is constant mass flow not unlike the Drägers, Azi and Submatix. The difference is that those units add more gas than the diver needs, 'burping' the excess. The KISS adds less and pure O2, and needs topping off every once in a while. If you get off the loop without shutting the valve down all of the units will have gas flow into the loop and vent it through their OPVs.

*Running for the bunker *

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nl_carey

SCRs are useful in their place, and the Dolphin was a great step forward as Caveseeker has said. And, until the Sporty came along, there were definite economic benefits to SCR's, including getting them, getting time on them, and then converting them to CCR's. Also, the SCR's were generally better setup for average diving, as rebreathers were mainly used for expedition-type diving.

caveseeker7

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Stefan


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