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All hail the mighty ZOM
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It would seem that twin 232 7's with an isolation manifold are an expensive way (Go-Dive 350 quid) to get exactly the same redundancy as a 232 15 with an H/Y valve (140 quid). Plus if one reg goes tonto then you can shut it off and have the full amount of air left rather than only 1/2, as with isolating one of a twin.
I appreciate that a single 15 will not be as nice to have on your back as twin 7's but it would be easier to mount (using a standard cam band on a stab jkt) and cheaper to maintain (1 test only).
The setup would be for recreational diving, 20-40m range with little decompression rather than anything deep and/or technical.
Your views would be appreciated, if a little apprehensively.
 

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<font color='#000080'>
[b said:
Quote[/b] ]It would seem that twin 232 7's with an isolation manifold are an expensive way (Go-Dive 350 quid) to get exactly the same redundancy as a 232 15 with an H/Y valve (140 quid). Plus if one reg goes tonto then you can shut it off and have the full amount of air left rather than only 1/2, as with isolating one of a twin.
The redundancy is not the same. If the problem is with the tank neck o-ring, you loose all of your gas with the single 15l. You can isolate the twins and save half of your gas. An H or Y valve on a single cylinder does not offer true redundancy like manifold twins (with an isolator).

I would seriously consider getting bigger tanks. You may think that twin 12s sound like overkill but they are perfect for the depth range you are talking about and you will be able to get two good dives from a single fill.

HTH.

Regards,

Mark.
 

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And what's more, twin 7s are lighter than a 15 (check the Faber site if you don't believe it) and spread the weight far more evenly.

Get a twinset. Far nicer


Tho I agree with Mark that 7s are a bit marginal for 40m dives.. unless you have a really good SAC
 

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<font color='#000080'>£350 for 232 7s from go-dive??


kent diving have 300 7s for £349 (including postage) that i'm currently lusting after
 

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<font color='#000080'>I've currently got 15's with H valves, but only as a stop-gap before getting twins. Mark is right about the issue of a valve seal bursting, but I've never seen it or spoken to anyone who has (and I spent quite some time asking around before I got my H valves). I'm happy that it is a negligible risk. Of course, twins have more seals to blow, so it is swings and roundabouts on that one.

I'd say 300 bar, manifolded twin 7's are preferable for a number of reasons. They are negatively bouyant which means you don't need to carry as much weight - a rig with twin 7's should be lighter than one with a single 15. Twin 7's are easier to swim with and more comfortable with a smaller profile. They do provide more redundancy. They work better with a wing than a single tank.

The downside is the one you've already recognised - increased maintenance costs and initial purchase cost.

Why not go the way I have? Fit H valves to your 15's until you've got the money for the twins. The 15 can always be used later for a second dive as your regs split for twins can be connected without any adjustment. It wouldn't be wasted money, and in the meantime you achieve the redundancy that you're after.

There was a thread going on this subject for some time while I was thinking about doing this. It's on the Equipment Forum. Search for Y-valves; that should find it. There should be plenty on there to help you decide.
 
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