Dry Suit Inflation System?

[Mr. Sunday]

Is a dry suit inflation system necessary? Im thinking of a pony type bottle mounted to a single main tank. What are it potential benefits or problems? Would it throw off your weight, etc? How large of a tank would be needed? I assume it could be used as a redundant air source also? Most diving would be done in the Pacific Northwest region.

Thanks

 

[DA Aquamaster]

Many people use a small pony bottle (6-13 cu ft) for a pony system. The real advantage here would be the ability to use argon for increased warmth. This requires additional hardware to transfill from a rented Argon tank, so it may or may not be cost effective for you. Unless you have access to a boost pump, you will be transfilling your tank and a low pressure (2015psi) pony makes sense as agron is only available at 2000-2200 psi. They offer a little more internal volume for a given dimensional size than a 3000 psi pony and will giove you more capacity at the low pressures available.

With air or argon, only the inflator hose is normally installed on the first stage. This then requires an overpresure relief valve to be installed on the first stage to prevent a rupture of a hose if the first stage freezes. It is also advisable to lower the IP on the reg being used to inflate the dry suit.

Another option for redundant inflation (usually with argon suystems) is to run an inflator hose from the back gas to supply the dry suit in the event you run out of argon. This hose is just kept tucked in until needed and then switched with the argon inflator hose underwater if needed. On the rare occasions I use argon this is what I do and the "normal" inflator hose becomes a redundant backup.

If diving doubles and not concerned about additional warmth, you can also add redundant inflation by running your dry suit inflator off one reg and your BC or wing inflator off the other. For me this approach makes the most sense most of the time. If I were doing long in water deco though, I would opt for an argon system.

Doing the same thing with a pony bottle makes much less sense as over time you deplete the air in the pony and at some point it will no longer have the capacity to be a safe redundant air supply. If you plan to use a pony for a redundant breathing air supply, confine it's use to brething air only.

As for weight and balance, a small pony attached to the perimeter holes of the back plate usually requires very little change in trim and ideally a pony bottle is balanced by a connister light on the other side. Attaching to the tank in my opinion creates additional drag and potential for entanglement and requires a longer hose. In either case it is worth considering inverting the tank so that it can be easily shut off if the need arises, but I would not lose sleep over it.

With a larger pony and nothign to counterbalance it, 2-3 pounds of weight may need to be moved to the other side. This is one area where weight integration shines as assymetircally loaded weight pockets don't slide around on you like an assymetrically loaded weight belt can.

 

[Bob3]

Is a dry suit inflation system necessary?

A drysuit inflation system becomes a necessity when using mixed gas or when you don't have enough (or any) LP ports on your reg.
Here are a couple threads on the topic:
http://www.scubaboard.com/showthread.php?s=&threadid=25192
http://www.scubaboard.com/showthread.php?s=&threadid=22940

I keep my little bottle hanging down off my butt, I dislike having extra stuff on my back, it has a tendency to grab lines, weeds, etc.
As DA Aquamaster mentioned, it's preferable to invert the bottle if its on your back. Makes clearing much easier.
Your mileage will no doubt vary.

 

[String]

..although whether Argon provides more warmth or is purely psychological is another debate all together

 

[DA Aquamaster]

I knew a diver you felt the second dive with argon was always warmer as all the air was purged from the suit on the first dive. He kept the suit on and sealed during the surface interval to maintain the argon in the suit.

The obvious solution of inflating and then purging the suit on the surface before the first dive never dawned on him. Argon is only warmer if it is mostly argon instead of a little argon added to the air already in the suit.

A lot of divers dive with very little gas in their suits, maintaining just enough to eliminate the worst of the squeeze. In my opinon that is diving with too little gas in the suit. Drysuits in general are warmer with a little more air space in them and if the suit fits properly you still will not have problems with the bouyancy shifting in the suit. but if you feel the need to keep a bare minimum of gas in the suit, Argon will keep you warmer than air.

I will weight myself according to water temp and add a bit more weight to allow a bit more air to be maintained in the suit in really cold water and the extra air (within reason) does keep you warmer.

With He mixes, as pointed out above, Argon is a gotta have item given the very high heat transfer that occurs both in your lungs and in the suit with helium.

 

[Atticus]

I will disagree with Aquamaster on just one point - I prefer to dive with very little gas in my dry suit and control buoyancy almost entirey with the BCD. I choose an undergarment that will trap enough gas in it to keep me warm for the conditions I dive in. His post and information is excellent.

This may be stating the obvious - but please, do not try to put a 2nd stage on an 'argon' bottle as the gas will not support life.

 

[Doc Intrepid]

kgdiver,

From the information you provided, the answer at this point in your diving career is "No, a drysuit inflation system is NOT necessary".

It is an expense you currently don't need, it adds weight and drag that you don't need, and for recreational diving in the Pacific Northwest the duration of your dives (you indicated you're using a single tank) are such that you're likely neither decompressing for long periods nor using trimix.

In short, the reason you might want a drysuit inflation system is if you were using argon to inflate your drysuit. As DAA and Bob3 noted, this would be the case if helium were present in your breathing mix. If helium was present in your gas, you would likely be diving with double tanks. If you were, then the length of your dives, the depth of your dives, or both, would likely keep you in the water much longer than typical recreational profiles. Thus, you'd use the argon to optimize your thermal protection.

While I am aware that some divers use a pony bottle as both an alternate air source and a BC inflation source, I don't see the utility of this in terms of expense, weight, drag, and maintenance/logistics.

In recreational diving there are occasions where an alternate air source is a good idea. In such cases you sling the bottle on your left side so you can get at the valve and/or hand the bottle off if necessary. The bottle (weight of the valve) also hangs beneath you and doesn't impact your lateral stability. In technical diving you will often have stage or decompression tanks slung on your left side. But IMHO there isn't much logic behind using a drysuit inflation system (or BC inflation system) that also is your alternate air source while using a single tank. If you want 'inflation redundancy' in the form of two tanks of gas on your back, get a set of doubles. Either inflate your drysuit with backgas, or use argon. Other options require a pretty convoluted rationale.

(If you want to use argon that's fine, if you have helium in your backgas, but you cannot simultaneously use argon as an alternate gas source.) Consider that all your tanks will require VIPs and hydros and fills, and (together with all your gear) must be transported and carried from here to there, etc. In general, try to reduce your gear load to as little as possible. If you don't absolutely need it, don't take it.

My .02 worth. YMMV.

(And by the way,...fill out your profile! Its often easier to respond more specifically if you know a bit more about the diver and the context of their question )

Regards,

Doc