Drysuit squeeze.

[g1138]

Dry suits also compress into folds (pressure points), neoprene doesn't.

That brings up an interesting point. Ive seen neoprene drysuits...BARE maybe? do those have the same feeling as say my Trilam? Or does the neoprene absorb some of the compression as opposed to folding...

I'm not as familiar with neoprene drysuits, but I think the squeeze is much less painful. You don't get paper thin folds, but folds might still be possible depending on how loose the suit is. You're undergarments are usually pretty thin which is where folds would most likely occur.
The neoprene material does compress with depth to a much greater degree than say trilam, which I don't think compresses at all.

 

[pasley]

The answer is - Air. Air compresses. Liquids (water) do not. Your body is mostly water so you would not notice the compression.

In a wetsuit Neoprean is made of air bubbles traped in rubber like material. As you decend these trapped bubbles compress (colapse) in on themselves but not on you. This makes the 1/4 inch or 9mm wetsuit thinner and therefore you colder. Because your external dimensions are less, and you are now displacing less water and must add air to hour BCD to compensate

In a drysuit - the air compresses and the bubble encasing it, the drysuit, compresses in on itself with you in the middle. You add air to maintain the loft and your warmth.

When teaching drysuit classes I warn my students that in the pool, floating at the surface they are going to feel the squeeze on their feet because for the first time their feet are encased in air, not water. They are always amazed at how you can feel it on your feet just 4 or 5 feet down from the surface as they float on the surface.

 

[spectrum]

In a wetsuit first of all there is no air in the equation. What happens to gas in the neoprene is irrelevant to the squeeze discussion. A wetsuit, being a wetsuit has any spaces filled with water. Where water is essentially incompressible once voids are filled they are going to be pressure neutral to the outside of the suit throughout the dive. Even if water were compressible it would be free to enter and exit as any pressure differential demanded.

Once you get into a drysuit there is some compressible air volume, you are in a collapsible container and it is sealed with the exception of the valves. In this case the pressure of depth will collapse the air in the suit (Boyle) beginning with a hug and eventually getting ugly if air is not added. If there were no air volume in the drysuit suit theoretically you would not need to deal with squeeze. The closest example I can think of is the old Skooba Totes 2 piece suits which could be very form fitting. Any incidental squeeze was (is) relieved by exhaling out of the mask seal into the hood and letting the bubble distribute. A well fit neopene drysuit can be comfortable to about 30 feet as it will have little compressible internal volume. A baggy laminate suit can be getting snug at half that depth and being baggy may pinch you in a fold.

It is an odd concept but I think the behavior of a zero air volume drysuit as an extreme leads to what happens in a typical drysuit and why it's a non issue when diving wet.

Pete

BTW The water bottle will crush when taken down and will rebound (as best it can), not pop the cap on ascent. The air volume will just rebound as it's the original content. A drysuit needs to be vented on ascent because air was added and if not released Boyle takes over and la la la loom.

 

[NAM001]

a wet suit will equilize because water flows through the suit. when in a dry suit ,(inside and outside presure keepig equal) a dry suit is much like your lungs,,, no way to equilize without taking in or letting out air from the water tight barrier which in this case the dry suit provides. with minimal air in the suit at the surface all is ok, when going deeper the differential presure makes the air compress in the suit. kinda like a what a food vaccumm machine does to a container with food in it. and like that food bag it crimps down on its contents untill you allow air to enter the bag and equalize the inside presure with the outside. your dry suit does not have to wrinkle up much before its live contents of various delicacy complains.

For some reason, I continue to struggle with the concept of why this happens. I dive a drysuit and am familiar with the squeeze you get as you decend. As you pump air into it, the squeeze is relieved...but WHY? 1 ATM on the surface your comfortable, 33 feet, 2 ATM its a little tight, 66 feet 3 ATM, suddenly you dont have the mobility to add air... How come this happens with the drysuit but not neoprene...or on bare skin? or boardshorts? There is no difference in pressure from one material to the other...the water column remains unchanged. If someone stands on your shoe, it hurts...if they stand on a pillow on your shoe...it hurts less...fine. But then if they stand on your bare foot, that hurts too! Ive kind of just accepted that it works the way it works, but every once in a while I try to reason through it and feel like I am missing a simple answer.

 

[freeclimbmtb]

When teaching drysuit classes I warn my students that in the pool, floating at the surface they are going to feel the squeeze on their feet because for the first time their feet are encased in air, not water. They are always amazed at how you can feel it on your feet just 4 or 5 feet down from the surface as they float on the surface.

This was the first thing I noticed when I got my drysuit wet for the first time. People compair it to fishing waders (for obvious reasons) but being that I am not a fisherman, I didnt have that frame of reference. Even now that I expect it, it still makes me smile when i get the "feet squeeze"


I do clearly remember in my training (both OW and AOW) taking a glass of air to depth to watch the bubble shrink and then re expand upon ascent. And while this illustrates boyles law well enough, I think a plastic bottle would have been a good addition to the demonstration. Seeing it actually crush in a similar manor to a drysuit, because a water glass upside down isnt going to deform and crush, because its a rigid vessel...like a diving bell.

So heres a demo i think i would have really connected with. Take a crushable bottle to depth...watch it start to collapse. then at depth, open it (upside-down) and purge a reg into it to refill it (this might work better with something more flexable than a water bottle) and restore the shape of the bottle...then cap it. then ascend with the bottle while NOT venting the air that was added. the bottle would expand and bloat, (and with a little luck...POP!) for me that would be the ultimate pre-drysuit demo

(and that could very well be the standard...but I didnt take the drysuit specialty class...I had someone show me how to recover from floaty feet...and started diving dry!!)

---------- Post Merged at 07:40 AM ---------- Previous Post was at 07:33 AM ----------

A more liberal instructor (with good humored students) Might take...how do I put this...an inflatable representation of a person...ahem...down to depth, then bump the air back up (just like shooting a bag right?), then watch the "volunteer" expand, bloat, and pop on the way up! (good way to show pulmonary barotrauma too...)

 

[NAM001]

great reinforcement for not holding yout breath.

This was the first thing I noticed when I got my drysuit wet for the first time. People compair it to fishing waders (for obvious reasons) but being that I am not a fisherman, I didnt have that frame of reference. Even now that I expect it, it still makes me smile when i get the "feet squeeze"


I do clearly remember in my training (both OW and AOW) taking a glass of air to depth to watch the bubble shrink and then re expand upon ascent. And while this illustrates boyles law well enough, I think a plastic bottle would have been a good addition to the demonstration. Seeing it actually crush in a similar manor to a drysuit, because a water glass upside down isnt going to deform and crush, because its a rigid vessel...like a diving bell.

So heres a demo i think i would have really connected with. Take a crushable bottle to depth...watch it start to collapse. then at depth, open it (upside-down) and purge a reg into it to refill it (this might work better with something more flexable than a water bottle) and restore the shape of the bottle...then cap it. then ascend with the bottle while NOT venting the air that was added. the bottle would expand and bloat, (and with a little luck...POP!) for me that would be the ultimate pre-drysuit demo

(and that could very well be the standard...but I didnt take the drysuit specialty class...I had someone show me how to recover from floaty feet...and started diving dry!!)

---------- Post Merged at 07:40 AM ---------- Previous Post was at 07:33 AM ----------

A more liberal instructor (with good humored students) Might take...how do I put this...an inflatable representation of a person...ahem...down to depth, then bump the air back up (just like shooting a bag right?), then watch the "volunteer" expand, bloat, and pop on the way up! (good way to show pulmonary barotrauma too...)

 

[Pane]

You want suit squeeze? I'll show you suit squeeze:

[video=youtube;DJn2dZq4bwk]http://www.youtube.com/watch?v=DJn2dZq4bwk[/video]

 

[fisheater]

You want suit squeeze? I'll show you suit squeeze:

[video=youtube;DJn2dZq4bwk]http://www.youtube.com/watch?v=DJn2dZq4bwk[/video]

Meat Man! My fav!


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[krawlings]

Here is my look at it Most dry suites are out of a material that does not change its thickness under pressure and is not fitted snugly to your body. So the matirial crushes around you unevenly . Know neoprene is fitted snugly around your body and it compresses evenly . there for wet suit compresses evenly and is still flexible for movement. dry suit becomes rigid and pinches

 

[fisheater]

Here is my look at it Most dry suites are out of a material that does not change its thickness under pressure and is not fitted snugly to your body. So the matirial crushes around you unevenly . Know neoprene is fitted snugly around your body and it compresses evenly . there for wet suit compresses evenly and is still flexible for movement. dry suit becomes rigid and pinches

Nope.

It's not the material or the compressibility of the material. It's just Boyle's Law working on the air spaces between the suit and the diver. You don't get a squeeze in a wet suit, because it's filled with water at the ambient pressure. Thus, no pressure differential. With a drysuit, the external pressure during decent exceeded the internal pressure (thus, the "squeeze"), until the diver added more pressurized air to equalize.

In other words, it works just like your ears.


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