Redundancy with a Single Tank

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msandler:
actually Mech, I didn't say that. Rephrase: Failures left unaddressed by a good H-valve setup are few.

Sorry, I didn't mean to infer I quoted you.

I see your reasoning for using an H or Y valve, but just think that, given the need, I would much rather have manifolded doubles. If the need is not present (most all rec diving IMO), then I would not bother with one.

MD
 
Seems to me that if you're looking for redundancy an H-valve will not do. An uncontrollable freeflow (edit: er, I dunno where I got busted hose from, but say a blown O-ring) will empty your tank, leaving no gas for either reg. With doubles you can plan for getting one tank emptied and always keep enough in *each* tank to get you to the surface, but you can't gas plan assuming a freeflow with an H-valve. With a pony you have a separate air source you can plan with too.

A good buddy seems to me to be the best redundant gas. You know they have enough, you know they're only a couple of seconds away, you know they have a working regulator to give you. Well... at least, all that should be true :wink:
 
On the rare occasions that I dive a single tank I use an h-valve. Mostly because I can but we dive cold water where a free flow is the most likely failure and when switching back and forth from doubles to a single I don't have to change over any regs. I just pull them off one and slap em on the other making both rigs exactly the same only one doesn't have the isolator.

In truth I have enough regs that I could just have a seperate one set up for a single tank but why?

I also like the way hoses rout off an h-valve better but it's not that big of a deal.

Another point, with regards to relying on a buddy as apposed to a redundant reg is that many of the shallow dives where I would dive a single tank are done with new divers or new buddies.

I'm not teaching now but I also got to like an h-valve for teaching. Shutting down a faulty reg and going to a backup rather than being tied to another diver would make controling a class while ending the dive easier even though I always have a buddy while teaching.

Ice dives are another time when I like an h-valve. I prefer doubles but if you have to walk a long way accross the ice to get to the hole they're a pain especially for the short shallow dives we usually do under the ice. Here again, we dive with 2 divers but the h-valve gives one more option in the case of the most likely failure...a free flow.
 
MikeFerrara:
I'm not teaching now but I also got to like an h-valve for teaching. Shutting down a faulty reg and going to a backup rather than being tied to another diver would make controling a class while ending the dive easier even though I always have a buddy while teaching.

Ice dives are another time when I like an h-valve. I prefer doubles but if you have to walk a long way accross the ice to get to the hole they're a pain especially for the short shallow dives we usually do under the ice. Here again, we dive with 2 divers but the h-valve gives one more option in the case of the most likely failure...a free flow.
Mike, when you were teaching using an H-valve, were you using 2 first stages then I presume? If so, did your students use the same setup? I'm just wondering how to explain to students why their gear config would be different than mine if I went to an H-valve with 2 first stages, while they are using single first stages on a K-valve. I could explain the redundant first stage part, but then they might wonder why their's isn't the same then.
 
Didn't somebody post once analyzing the time required to shut down a manifolded double vs. the time for a severed LP hose (or similar major breech) to empty the tanks and find that it was a fairly close race?

I can't find the post at the moment, but I recall it being fairly interesting in this context. Anybody else remember/find this?
 
Another good argument for your buddy.
 
Warren_L:
Mike, when you were teaching using an H-valve, were you using 2 first stages then I presume? If so, did your students use the same setup? I'm just wondering how to explain to students why their gear config would be different than mine if I went to an H-valve with 2 first stages, while they are using single first stages on a K-valve. I could explain the redundant first stage part, but then they might wonder why their's isn't the same then.

Other than the dual 1st stages we were rigged the same...longer primary which gets donated and backup on a necklace. The dual output valve and first stages is something I show and explain both in class and in the pool.

Equipment configuration in general is something that I always spent a good deal of time on.
 
lairdb:
Didn't somebody post once analyzing the time required to shut down a manifolded double vs. the time for a severed LP hose (or similar major breech) to empty the tanks and find that it was a fairly close race?

I can't find the post at the moment, but I recall it being fairly interesting in this context. Anybody else remember/find this?

I think I remember this.

I was speaking to a guy once who dove independents. He said his reason was that once at 60m (180ft) on trimix, he was just about to start his ascent when he had a giant freeflow. He said he literally thought "wtf???" and started to reach behind his head when all his hoses went slack. He had to go onto his 50% at 60m because all he had was 50 and 100%.

So he now dives independents. This adds a few problems and solves a few problems but for him it was much safer - since I believe most of his diving was virtually solo (same ocean buddy at the very least).
 
jonnythan:
Seems to me that if you're looking for redundancy an H-valve will not do. An uncontrollable freeflow (edit: er, I dunno where I got busted hose from, but say a blown O-ring) will empty your tank, leaving no gas for either reg.

Not true, you can shut the valve to the faulty reg.

Mech, no problem. I have and will use an H-valve where a reasonable amount of redundancy is required and the mass or size of doubles is too cumbersome/difficult to be justified.
like the back of a skidoo or a leisurely deco dives. I know most would find this unacceptable and you won't get any argument from me, nor I am not trying to pursuade others. Just my to cents.
 
jonnythan:
Seems to me that if you're looking for redundancy an H-valve will not do. An uncontrollable freeflow (edit: er, I dunno where I got busted hose from, but say a blown O-ring) will empty your tank, leaving no gas for either reg. With doubles you can plan for getting one tank emptied and always keep enough in *each* tank to get you to the surface, but you can't gas plan assuming a freeflow with an H-valve. With a pony you have a separate air source you can plan with too.

There's no way to recover from a blown tank oring with an h-valve but I've never seen one of those in the water have you?

An h-valve does provide a way to manage the most common failures though.
A good buddy seems to me to be the best redundant gas. You know they have enough, you know they're only a couple of seconds away, you know they have a working regulator to give you. Well... at least, all that should be true :wink:

I don't use either an h-valve or manifolded doubles in place of a buddy. I use them in addition to a buddy.
 
https://www.shearwater.com/products/perdix-ai/
http://cavediveflorida.com/Rum_House.htm

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