Wet, doubles, LPI hose. Why no redundancy?

[stuartv]

I have looked at the DIR and GUE pages on hose configuration and routing for diving doubles. They both say the same thing my Tech instructor did. So, when diving in a wetsuit, there is only one LPI hose in the configuration that is specified.

The DIR and GUE texts both make points about why the LPI hose is on the right post and how much of a problem it could be if it was on the left post and you had an accidental roll-off. So, if that is so much of a concern, what about if you HAVE to shut down the right post? With the specified configuration you would now have no way to inflate your wing at all, other than the oral inflator.

It seems like these "recommended" configurations would have at least one of the following:

- require a dry suit
- require a dual bladder wing
or
- require a redundant LPI hose on the left post that is clipped off or tucked somewhere, so you could switch to it in an emergency

And also require that the LPI hose on each post be long enough to reach the LPI and the dry suit inflator (if diving dry), so you could use a LP hose from either post to do either job (wing or dry suit).

Why is none of that there? Do people diving doubles in wet suits just not worry about losing their only wing inflator?

You assume you'll be neutral if/when you have to shut down the right post, so you can swim up, the wing expands, and then all you need is to be able to dump gas, not add it? And you'll add via oral inflator if you end up needing to?

For that matter, what about diving dry and having to shut down your left post? It seems like the LPI hose for my DSS wing is pretty typical in that there is no way it would reach my dry suit inflator to use it for that, if needed.

Having the oral inflator as your only redundancy (and no redundancy for the dry suit inflator at all) is surprising to me, given the stress placed on redundancy in every other area.

 

[nimoh]

what's wrong with oral inflation of the wing?

personally, I see the power inflator as more of a convenience than a necessity.

 

[tbone1004]

I actually put my drysuit on the right, inflator on the left due to preferring to orally inflate in case of a rolloff, but you are correct, if that post fails, you can no longer inflate your drysuit, potentially problematic, though in a real pinch you can be creative and inflate via a wrist seal, not ideal but it can be done. That said, a LPI hose coming from the left should be able to reach the drysuit inflator over your right shoulder. Some suits used to have an oral inflator nipple on them, but if you look at the physics of the gas bubble on descent, if you're below 30ft, then you can go quite a ways down before having to actually add air. The pressure gradient is not linear, so the worst squeeze is the first 33ft, then it eases up from there, but to get that same squeeze in the first 33ft, you have to go all the way down to 100ft, so you've got a long way to go before you really NEED to inflate the drysuit to keep you from not being able to have children. Sure you'll get a little chilly, but if you're diving cold water suits, you have a boat load of air in there and if you're comfy at 33ft, you can probably go down to 100ft and aside from getting chilly from lack of airspace, you shouldn't be squeezed too hard. I can't think of any caves that have that big of a pressure differential for return home. I'm sure they exist, but I have inflator hoses on all of my stage bottles just in case ;-) *really it's for ease of analyzing gas, but it's an extra perk*. If you're in OW, you'd come up and there is also basically 0 risk of a rolloff.

Regarding redundancy of the power inflator, what is wrong with orally inflating? That is the only form of inflation our students are allowed to use during all of their pool training, and only one allowed at the surface period. Redundant buoyancy is there for a total wing failure, not an operator error of not being able to orally inflate. This is why we teach oral inflation from day 1, if that is the first way you learned how to control your buoyancy, in the case of an OOA situation where you had a total gas failure, or like this where you had a post failure, your brain reverts back to oral inflation instead of power inflation.

These scenarios are no different than single tank diving btw....

 

[PfcAJ]

I have looked at the DIR and GUE pages on hose configuration and routing for diving doubles. They both say the same thing my Tech instructor did. So, when diving in a wetsuit, there is only one LPI hose in the configuration that is specified.

The DIR and GUE texts both make points about why the LPI hose is on the right post and how much of a problem it could be if it was on the left post and you had an accidental roll-off. So, if that is so much of a concern, what about if you HAVE to shut down the right post? With the specified configuration you would now have no way to inflate your wing at all, other than the oral inflator.

It seems like these "recommended" configurations would have at least one of the following:

- require a dry suit
- require a dual bladder wing
or
- require a redundant LPI hose on the left post that is clipped off or tucked somewhere, so you could switch to it in an emergency

And also require that the LPI hose on each post be long enough to reach the LPI and the dry suit inflator (if diving dry), so you could use a LP hose from either post to do either job (wing or dry suit).

Why is none of that there? Do people diving doubles in wet suits just not worry about losing their only wing inflator?

You assume you'll be neutral if/when you have to shut down the right post, so you can swim up, the wing expands, and then all you need is to be able to dump gas, not add it? And you'll add via oral inflator if you end up needing to?

For that matter, what about diving dry and having to shut down your left post? It seems like the LPI hose for my DSS wing is pretty typical in that there is no way it would reach my dry suit inflator to use it for that, if needed.

Having the oral inflator as your only redundancy (and no redundancy for the dry suit inflator at all) is surprising to me, given the stress placed on redundancy in every other area.

Roll off means surprise lack of ability to use the LPI. If you're forces to shut down the right post its not a surprise anymore. Imagine coming out of a smaller area in a cave ~100ft deep that's rolled off your left post and now you're over a sheer drop to 200' (that's a real thing, btw). Surprise inflator failure is gunna suck real bad.

Double bladder wings are fraught with issues. See other threads about them
Drysuit is a good idea, especially for heavy steels. With al80s, you can swim against them so its not required.
Extra LP hose is just ONE MORE thing to fail that just sits there for 99.999% of dives, and really adds no value as you can still orally inflate.
You don't want to inflate your suit with backgas on a trimix dive, and doubles often imply deeper diving with helium.

No, I don't worry about losing my LP inflator when diving a wetsuit. I can orally inflate, no big deal.

You can always open your post momentarily to add gas to the drysuit. Nothing wrong with that. Deeper dives imply argon (or airgon due to helium in the backgas.

Focus on redundancy is for the important stuff like being able to breath and see, not convenience items like power inflation of the wing and your drysuit. Once you're at depth with the suit you tend to not fiddle with it much anyways. DIR is also about minimalism which is often overlooked.

 

[abscuba]

You can orally inflate, you can also use your smb in an emergency to help with lift, or even a lift bag if your kit has one.

 

[stuartv]

I cannot answer the question "what is wrong with oral inflation." I don't feel I have the experience. It is a question in my mind because, if the answer is "nothing", it makes me wonder why the GUE and DIR explanations make such a big deal of having the LPI hose on the right post. It seems like not having a 90 degree bend in the hose right as it comes out of the 1st stage would be a good reason to put the wing inflator on the left post. And then, the DIR and GUE response to "what if I have an accidental left post roll-off" would be "use your oral inflator as necessary until you turn the left post back on."

In other words, the negative repercussions of having an accidental left post roll-off (a very occasional occurrence) affect your inflator seem (to me, the newb) pretty inconsequential compared to putting the stress on that LPI hose where it comes out of the 1st stage (100% of the time - assuming you're not using a 1st with a LP port on the bottom).

In other words, since DIR and GUE seem to think it's so important to not have a momentary interruption in your ability to use the LPI hose, it gave me the impression that it's too important to have the redundancy be the oral inflator.

---------- Post added August 12th, 2015 at 11:55 AM ----------

Imagine coming out of a smaller area in a cave ~100ft deep that's rolled off your left post and now you're over a sheer drop to 200' (that's a real thing, btw). Surprise inflator failure is gunna suck real bad.

Thanks for all that. I think I understood it all, except for the part I quoted. I have swum out past the edge of a drop off before. My depth remained the same. Why do you say that an inflator that doesn't inflate is gonna suck real bad at that point? A BC failure where you suddenly lose buoyancy? Yes, I can see that sucking. Not being able to add gas to your wing? I don't see how swimming past the edge of a cliff makes any difference to that.

 

[PfcAJ]

When you start descending (who would wan't to turn around at the coolest part of the dive? not me!) is when the suckage will begin.

 

[abscuba]

I have LP hoses on all my tanks, however that is for off board on my rebreather but it could be used for my wing in a pinch. Unless your tank is empty or there is a catastrophic failure in the hose there is no real place for the LPI not to work. If the power inflator has failed then another LPI will probably not help. And like you said if your buoyancy is already set then coming out of a cave would not change it. It would really only be an issue on the initial decent when larger amounts of gas are added to the wing. To add to this the most LP hoses you add to tanks does add more failure points in the system for something to go wrong and cause a lost gas situation.

 

[eelnoraa]

I can see one of the reason is if your LPI start to auto inflate, you can use your left hand to vent the wing while shutting down the right post to mitigate the issue. If you have LPI on left, which one will you do?

 

[AJ]

It is a question in my mind because, if the answer is "nothing", it makes me wonder why the GUE and DIR explanations make such a big deal of having the LPI hose on the right post. It seems like not having a 90 degree bend in the hose right as it comes out of the 1st stage would be a good reason to put the wing inflator on the left post. And then, the DIR and GUE response to "what if I have an accidental left post roll-off" would be "use your oral inflator as necessary until you turn the left post back on."

It's all about seperation of buoyancy resources. Right = Wing, left = dry suit. Yes, dry suit is the standard config with GUE. Especially when you are diving with steel doubles. If one post fails, you still have buoyancy control trhough the other post. In an emergency situation you don't want spend time orally inflating your wing. You want to get control of the situation and buoyancy asap. Only as a last resort you can rely on oral inflation, but I would not recomend it while doing long deco.

In other words, the negative repercussions of having an accidental left post roll-off (a very occasional occurrence) affect your inflator seem (to me, the newb) pretty inconsequential compared to putting the stress on that LPI hose where it comes out of the 1st stage (100% of the time - assuming you're not using a 1st with a LP port on the bottom).

There should never be so much stress that this poses a problem. If it does, your routing is not correct. In the end hoses will wear and tear and need to be replaced. Just check them regurlarly.