Dry Suit with Auto Dump Valve

[jamesadele]

More great posts. Feel like I am building a picture of how these things should be use now so will have to write down the key points from all these points and try them out this week.

@JohnN We are doing a PADI Open Water and in fact this sunday will be the last time we dive before being qualified. Our instructor is brilliant and quite easily one of the best and most interested tutors I have ever had on any subject. He went out of his way to help and maybe this week he may try doing as has been suggested a few times here and she will have to use the BCD. The guy really wants us to learn in our dry suits though because he says if we can learn those its a good skill to have and we can drive almost anywhere and that ocean diving will be a dream compared to it.

 

[decompression]

I know you probably wouldn't change instructors but in my experience (20yrs diving, 4000+ dives, instructor for over 10yrs, PADI/SDI/TDI/UTD), this advice/technique is highly questionable. There may be more behind it that I don't know. But, the inherent dynamic instability of a drysuit with a lot of air in it is just dangerous.

 

[fire_diver]

Just do the class as your instructor wants. When you are done with the training, practice different techniques on your own and decide what works best for you. You may decide you like DS only for buoyancy or you may find you prefer to just use it for warmth.

Try not to stress too much, and don't be afraid to ask your instructor questions. Scuba is supposed to be fun and relaxing!

 

[Storker]

the inherent dynamic instability of a drysuit with a lot of air in it is just dangerous.

If you aren't grossly overweighted, you won't have "a drysuit with a lot of air in it". You'll have a drysuit with some air in it.

When I started diving, I inflated my BCD only on the surface and used my suit for buoyancy adjustments during the dive, since managing a single air volume uses less mental bandwidth than managing two air volumes. That was the right thing for me, at the skill level I was at. These days, I prefer using my wing for primary buoyancy control, since it vents faster, and I only add just enough air to the suit to avoid squeeze and to keep warm. Even then, my wing is more or less empty at the end of my dive due to the buoyancy swing of my tank, and I just have enough air in my suit to offset squeeze. That suit air still provides a significant amount of buoyancy, though.

As others have said, the OP should do the course and then find out what works best for him.

 

[Phil_C]

A number of different courses I have seen being run for entry level drysuit diving have emphasised this idea of only using BC on the surface and using the drysuit for buoyancy during the dive.

When I have asked for the instructors rationale they have said because using BC and drysuit together gives two air volumes for new divers to contend with, and often they get confused with which one they need to vent to correct their buoyancy. (Mind you when I have asked the instructors have not always been able to articulate why they are doing it this way).

An instructor tried to teach me this way when I first started drysuit diving (after a couple of hundred wetsuit dives) wanted me to use drysuit only, but all that did for me was ended up putting a big bubble of air in the suit which kept moving to where I didn't want it at the most awkward of times

I changed to drysuit for warmth and comfort from squeeze, and set the auto dump for my depth, then used my BC or wing for anything else and have not looked back since.

You may find the instructor is trying to teach you drysuit only for the same reason, one less task for when you are learning.

I fully agree with them that if you can dive UK drysuit open water year round, then somewhere like the Mediterranean or an Egypt live aboard will be a doddle. So as others have said stick with it, then when you are qualified make a few dives just to practice and get the feel for what is happening, stay shallow, and just play around, come to really understand instinctively what is going on with buoyancy, then you will be able to decide for yourself what method suits you best. Good luck - Phil.

 

[Edward3c]

More great posts. Feel like I am building a picture of how these things should be use now so will have to write down the key points from all these points and try them out this week.

@JohnN We are doing a PADI Open Water and in fact this sunday will be the last time we dive before being qualified. Our instructor is brilliant and quite easily one of the best and most interested tutors I have ever had on any subject. He went out of his way to help and maybe this week he may try doing as has been suggested a few times here and she will have to use the BCD. The guy really wants us to learn in our dry suits though because he says if we can learn those its a good skill to have and we can drive almost anywhere and that ocean diving will be a dream compared to it.

Hi James,

First thing is its NOT an automatic dump, its a constant volume valve. The idea is when you get to your operating depth (20m) and achieve neutral buoyancy you might have, say 4Lt of gas in the suit. As you ascend to say 10m the gas expands (Boyle's Law), to maintain the 4Lt volume the valve vents off the excess gas. Those diving with valves on their wrists (cuff-dump) have to lift their arm to vent the expanding gas. The point about closing then winding back a number of 'clicks' only works when you've determined the strength of the spring and what suits you.

However, don't be down-hearted dry-suits do take time to get used to. Aster many years I still remind myself to drive my suit.

Whilst your still learning the finer points of all your kit it makes sense to look at controlling one air source for buoyancy, later on you can, if you wish, use your jacket for buoyancy and only put enough gas into your suit to prevent squeeze. I ran a BSAC Buoyancy & Trim Workshop last Saturday.

Kind regards

 

[decompression]

If you aren't grossly overweighted, you won't have "a drysuit with a lot of air in it". You'll have a drysuit with some air in it.

When I started diving, I inflated my BCD only on the surface and used my suit for buoyancy adjustments during the dive, since managing a single air volume uses less mental bandwidth than managing two air volumes. That was the right thing for me, at the skill level I was at. These days, I prefer using my wing for primary buoyancy control, since it vents faster, and I only add just enough air to the suit to avoid squeeze and to keep warm. Even then, my wing is more or less empty at the end of my dive due to the buoyancy swing of my tank, and I just have enough air in my suit to offset squeeze. That suit air still provides a significant amount of buoyancy, though.

As others have said, the OP should do the course and then find out what works best for him.

If the instructor is having them use the DS as buoyancy what are the chances he will have ow students "overweighted"?

 

[industrious95]

I'll share how I was taught, which seems to be contrary to a lot of the other advice you've already gotten. But you did say your instructor wants you to use the dry suit for buoyancy, which is how I was taught.

I enter the water with the dump valve completely open. When I begin my descent, I raise my arm to get the last of the air in the dry suit out. At about 5 feet, I close the valve 4 clicks, and fill the suit with air as I descend to prevent squeeze. When I reach the bottom, I make any final adjustment for buoyancy.

When I complete my dive, I open the valve completly and begin my ascent. I raise my arm to vent air as necessary, to control my ascent rate, and to maintain proper depth for my safety stop.

When I reach the surface, depending upon the conditions and how far I am from the ladder, I may add air to help me float. Usually, I can float at the surface with the little bit of residual air left in the suit, but if the seas are rough and there's 5 divers ahead of me at the ladder, I'll close the valve a bit and inflate.

 

[TSandM]

You know, I was originally taught dry suit for buoyancy, and I had a heck of a time with that. But, of course, I was grossly out of trim and not very stable. I don't think I was overweighted; I certainly listened to the information on proper weighting in my class, and by the time I got to Fundies, six months after I got certified, I had my weight pegged. But running enough air in the suit to get neutral was more than I could manage on ascent, so I found that running the suit tight and putting air in the wing worked better (although I was cold).

Ten years later, I run all the compensatory air in my suit up to 100 cf tanks. Beyond that, I have to use some wing. About 7 lbs of compensatory gas is all my suit will comfortably hold without auto-venting, and beyond that, my feet are so sloppy I feel as though I will lose my fins. But it is quite possible to run 7 lbs of gas in the dry suit and manage it neatly. It just requires enough experience to be able to control one's attitude and posture, and enough bandwidth to stay ahead of buoyancy changes and vent the suit before you are hopelessly behind.

 

[Storker]

If the instructor is having them use the DS as buoyancy what are the chances he will have ow students "overweighted"?

Overweighted? Most probably.
Grossly overweighted? I hope not, at least if the instructor is competent. But I'll give you even odds on the bet.