LP Inflator Hose - Right Post - Why?

[Scared Silly]

Okay so I set up a set a doubles for me and nice fat single tank with an H valve for the wife on a recent trip. As we were setting things up we were going over hose routings and the usual who is one first as this was her first time using an H valve rig. The backup first/second stage and the HP hose went on the left or seconary post. And the primary first/second stage and LP hose went on the right or main post. So when asked about why HP on the left I said that in case you have to shut down the main post you can still monitor your gas while aborting the dive. So using the same logic she then asked why is the LP on right as after all if you lost the main post you would also lose the LP inflation. Even after doing some reading and search I could not really offer a good answer so I thought would ask.

 

[Reinoud]

Okay so I set up a set a doubles for me and nice fat single tank with an H valve for the wife on a recent trip. As we were setting things up we were going over hose routings and the usual who is one first as this was her first time using an H valve rig. The backup first/second stage and the HP hose went on the left or seconary post. And the primary first/second stage and LP hose went on the right or main post. So when asked about why HP on the left I said that in case you have to shut down the main post you can still monitor your gas while aborting the dive. So using the same logic she then asked why is the LP on right as after all if you lost the main post you would also lose the LP inflation. Even after doing some reading and search I could not really offer a good answer so I thought would ask.

Imagine that you donate air to your buddy. She is on your longhose and you are on the backup.
Now something else goes wrong and you loose the left post during a small passage. At this moment buddy-breathing is not an option. So you can still breath from the inflator hose (not from the wing but directly from the hose by pushing both buttons simultaneously).
Obviously, if the inflator was connected to the left post this would not be possible.

Loosing the inflation of your wing if the right post fails is not really a problem: you can still inflate it orally.

 

[pcowboy6196]

I think that the DIR answer would be because in an overheard environment if you were to hit the ceiling with your tank the primary or right post would roll toward open where the left post would roll shut. You need your long hose and lp inflator for bouyancy control and as backup breating option. The reason that the SPG is on the left and wouldn't matter if the valve was shut is that you should be able to estimate your gas remaining to +/- 200psi without looking at the SPG.

*info from DIR: Fundamentals of Better Diving

-Wes

 

[PerroneFord]

So using the same logic she then asked why is the LP on right as after all if you lost the main post you would also lose the LP inflation. Even after doing some reading and search I could not really offer a good answer so I thought would ask.

I'm trying to imagine an abort situation where I'd want to ADD gas to the wing rather than vent. Perhaps in a cave where you'd have to go though a tunnel that dipped down before rising to get out, but in that situation you could inflate orally. In open water, you'd be venting gas, not adding it.

 

[Reinoud]

I think that the DIR answer would be because in an overheard environment if you were to hit the ceiling with your tank the primary or right post would roll toward open where the left post would roll shut. You need your long hose and lp inflator for bouyancy control and as backup breating option. The reason that the SPG is on the left and wouldn't matter if the valve was shut is that you should be able to estimate your gas remaining to +/- 200psi without looking at the SPG.

There is another reason to put the SPG left: if your manifold is accenidentally closed, you will notice after some time that you seem to be consuming no gas. (because you only breath the right tank).
At that moment you want to abort the dive, because it might not be clear *when* the manifold was closed. Was is before the blending of the back gas? So you are not sure what mix you will be breathing if you open it...

 

[King Kong Matt]

GUE's explanation, from http://www.gue.com/Equipment/Config/index.html

Power inflator hoses should run over the diver's left shoulder and be long enough to comfortably supply the power inflator, while not so long that they bulge out to either side. In turn, the inflator itself should be long enough that, with one hand controlling all maneuvers, a diver is able to easily reach his/her mouth, his/her dry suit inflation valve, and his/her nose; it should also be long enough that, if necessary, one could breathe out of it by simultaneously holding down both buttons.13 The inflator from the wings runs over the shoulder and through a small bungie attached with the left chest D-ring. This keeps the inflator where it can be located instantly.

To provide additional redundancy when using two first stages, the inflator hose should always be run from the right post. This requirement is illustrated in the case of a diver's left post rolling off or breaking. If the inflator is run from the left post, the diver will simultaneously lose not only the use of the backup regulator around the neck but also the ability to inflate the BC. These two problems together could be inordinately compounded by an out-of-air situation in which a diver would not only be without the means of controlling his/her buoyancy but would also be deprived of the use of a third regulator (cf. note 7).

 

[Scared Silly]

Thanks for the explaination - I missed some of this in the DIR Fundies book of mine. I will try to find it and reread it. That said this makes sense in the context of doubles and the left post roll off and the need for a redunant system when donating.

So how about with an H valve where this is not a problem because the valve is vertical and rolls on? My answer is because of consistency. Even though we have a different value system we should both have the same hose set up so either of can aid the other in case of problem.


Also here is a side question. I set my wife up on the H valve system on a steel 112 during our trip to Truk Lagoon because I felt it was the safest way for her to have a redundant system without carrying a pony bottle. One rarely sees H valves in use - in fact one of the dive crew who was an instructor said that it was the first time he had seen one other than in pictures. So although this is after the fact I would be interested in other people's thoughts on the use of H valves. If you are going to dive in this type of an environment with a single tank what is perfered system?

 

[lamont]

it also keeps active on right, backup on left.

 

[DIR-Atlanta]

I set my wife up on the H valve system on a steel 112 during our trip to Truk Lagoon because I felt it was the safest way for her to have a redundant system without carrying a pony bottle.

Cobb's Law applies here - "If you think you need a pony bottle, then what you really need is doubles." I suspect that a set of double 80s would be much easier for your wife to manage than a huge steel tank, and she could carry more gas to boot.

So although this is after the fact I would be interested in other people's thoughts on the use of H valves. If you are going to dive in this type of an environment with a single tank what is perfered system?

H valves provide some redundancy to be sure, but they actually have more "single points of failure" than either a standard K valve or a manifold. Besides the obvious ones (tank neck O-ring and and burst disc), there is also the mechanical connection between the left and right sides. It's the same type of connection as a manifold, but does not provide any capability to isolate if the connection fails. For that reason, I personally consider them less desireable than either a single tank or a set of properly manifolded doubles.

If you are absolutely convinced that a dual regulator setup on a single is what you want, then I would look at a valve with a mono-block design, such as the Beuchat Y valve:


Click the images for a larger view

Note that I do not consider this a "true" DIR solution.

I think what you really need to do is take a good hard look at what problem you are trying to "solve" with the H valve setup. Are you worried about insufficient gas for the dive? Added redundancy in case of emergency? Something else? Tell us what your exact concerns are and we can probably provide a more targetted response or suggestion to address that issue.

 

[pcowboy6196]

There is another reason to put the SPG left: if your manifold is accenidentally closed, you will notice after some time that you seem to be consuming no gas. (because you only breath the right tank).
At that moment you want to abort the dive, because it might not be clear *when* the manifold was closed. Was is before the blending of the back gas? So you are not sure what mix you will be breathing if you open it...

I am sorry but this doesn't make sense to me. Wouldn't one always analyze their gas before diving it? also wouldn't one know if they were or not blending tanks together with the manifold on or off? and would one also have the same gas in both back tanks and verify isolation maniford is open and that the gas is the correct mixture before diving it? Using what you said would make sense to me if the person in question doesn't believe in doing their pre-dive checks and gas analyzing. Please correct me if I missed something.

Wes