Octo questions

[tmds]

I guess it would be funny to ask if anyone had an opinion (everyone does), but is it safe to use a normal second stage as an octo instead of buying a specific octo. I have a scubapro MK25/S600 and would be adding a G500 as the octo. I've read threads that there is a problem with free flow at the surface, but I can deal with that if I don't have to spend alot money to buy a specific octo.

Thanks
Tom

 

[DA Aquamaster]

Scubapro's octos are identical to the same model second stage when used as a primary with one or sometimes 2 differences in how they are set up.

Generally speaking an octo is adjusted to have a cracking effort about .5" of water higher than when used as a primary. This is however optional, and there is a lot of merit in having your octo perform as well as your primary.

On some SP second stages, the VIVA flow vane can be reversed to reduce the venturi effect. This is normally a good idea when the second stage is set up as an octo. But then again, if the second stage has an adjustable flow vane, leaving it set at the (-) setting will pretty much preclude the potential for a freeflow during the dive.

The most important consideration is to have the G500 tuned to the Mk 25 to ensure that it is compatible with your particular first stage's intermediate pressure. At this point you can also have the cracking effort set to a slightly higher value if you desire. The normal inhalation resistance range for a G500 is 1.0 to 1.4 " of water. I'd probably ask the tech to set it around 1.2 to 1.4 and leave it at that as the flow vane adjustment itself will prevent a freeflow.

The US made G500 (all black purge cover) is a very sweet breathing regulator and is every bit as good as the S600. The later Italian made G500's (black and grey purge cover) were not quite as nice breathing, but the good news is that the Italian version can be upgraded to S600 status fairly inexpensively as they share the same case.

Personally, if I owned a US made G500, I'd give serious consideration to using it as my primary and use the S600 as the octo as the breathing performance is essentially identical. The G500 does not have the sometimes problematic seat saver feature that is found on the S600 the has a better record of reliability in cold water.

If I owned an Italian made G500, I'd consider getting it upgraded to S600 status (as long as your LDS is not gouging you too much on parts cost). Very little additional labor is involved if you have it upgraded at annual service.

 

[rescuediver009]

It shouldn't be too much of a problem but just know that you won't be able to get the best possible performance out of it as in addition to detuning it as an octo, you will have to further detune it as the MK25 is overbalanced and will increase the ip to more than what the unbalanced finely tuned second stage is suited for. But if you are not too deep, dark, or cold, it shouldn't be too bad.

 

[tmds]

It shouldn't be too much of a problem but just know that you won't be able to get the best possible performance out of it as in addition to detuning it as an octo, you will have to further detune it as the MK25 is overbalanced and will increase the ip to more than what the unbalanced finely tuned second stage is suited for. But if you are not too deep, dark, or cold, it shouldn't be too bad.

I'll only be using it on a cruise with my wife to the caribbean this winter and would rather do this than use rental gear. I'm going to take it to the LDS and have them take a look at it first. Sounds like that is what I should do. Will I have to get it tuned again for the MK20 it came off of? Probably will, huh.

Tom


Also it has a black purge cover with a grey S on it. Is this US or European?

Thanks

 

[rescuediver009]

I'll only be using it on a cruise with my wife to the caribbean this winter and would rather do this than use rental gear. I'm going to take it to the LDS and have them take a look at it first. Sounds like that is what I should do. Will I have to get it tuned again for the MK20 it came off of? Probably will, huh.

Tom

Won't hurt. differences in the MK20-25 are technical (IP adj.) and minute others. The balancing should be the same however I would get it tuned properly as there is always the slightest IP differential.

Also it has a black purge cover with a grey S on it. Is this US or European?

Thanks

and, no.

 

[DepthCharge]

It shouldn't be too much of a problem but just know that you won't be able to get the best possible performance out of it as in addition to detuning it as an octo, you will have to further detune it as the MK25 is overbalanced and will increase the ip to more than what the unbalanced finely tuned second stage is suited for. But if you are not too deep, dark, or cold, it shouldn't be too bad.

[FONT=Comic Sans MS]IIRC the G500 is a balanced 2nd stage[/FONT]

 

[rescuediver009]

My mistake for whatever reason I thought we were talking genesis.... I think that it would be balanced.

DA- what is the difference between this and the S600 and why is the MK25 all black in some pictures when paired with this reg?