Why do you get dry suit squeeze and not wet suit squeeze?

[markr]

Hmmm, I wonder if you had a really, really good semi dry wetsuit, dived down quickly, could you get a squeeze for a short time till it equalizes?

I've never worn a dry suit so I'm not sure if the feeling is exactly the same, but you can get squeezed and pinched in a semi-dry wetsuit, and it doesn't require a rapid descent. The legs of my suit are a little longer then they need to be. If I pull the legs of my suit up to far a fold forms which can pinch. Letting water in stops the pinch. Making sure the legs are pulled down towards my ankles so there is no folding in the crotch area prevents the pinch, however there is still a squeezing sensation if I don't get water in the suit.

The first time it happened, I really didn't think about the physics involved, makiing it stop was the main concern.

After reading some of the comments on this thread, I'm not sure if the problem is caused by the air in the suit getting compressed or that air pockets in the suit allow the pressure to be felt unevenly. Basically the spots where there isn't air are felt as a hard surface while the places where there is air between you and the suit are felt as a soft surface. Having water in the suit isn't going to reduce the pressure on your body but it will make the application of pressure uniform across the surface area and less noticable. The pressure on the inside and outside of the suit are going to be the same either way.

 

[rakkis]

An air pocket around a patch your skin, literally sucks on yoru skin like a hickey as the air pocket shrinks.

It can happen on a wet suit too, but it tends not to becuase of the fit, as other posters have mentioned. I got squeezed where you don't want to get squeezed the first time I wore my semi dry - I didn't pull the suit up along my legs all the way

 

[Xman]

Actually, it IS a fixed volume.. Its not like the fabric and surface area get smaller when it get squeezed together
Alas, the maximum volume of air (or water) it could hold is the same wether its fully inflated or fully deflated....snip..

Ahhh, no it isn't. Just because it has a fixed MAXIMUM volume, does not mean that it has a FIXED volume. It can get smaller by the outward facing curves inverting, or by simply flattening out. Is a tent the same volume packed away as when erected??

 

[Gombessa]

Well, if we're going to delve into the technicalities, the answer would obviously depend on how well you either pack away or erect the tent!

 

[Thalassamania]

The pressure is always the same inside and out- but if you don't add any additional gas to the inside of the drysuit, it shrink wraps you to compress the volume and equalize the pressure.

Yes, the question is does it equalize pressure with more gas or by sucking your flesh into the lower pressure area, that's what squeeze is.

 

[Soggy]

Did we all just forget about Boyle's law when we put on drysuits?!

Apparently the balloon analogy was missed by some.

Picture your drysuit, sealed up, pumped with air and sealed at the neck and wrists. You are not in your drysuit.

Now bring just the suit down to 100 ft. The gas inside the suit will compess to roughly 1/4 the volume that it was on the surface. The suit, because it is made out of flexible fabric, will fold and crumple in order to accommodate the reduced volume inside.

Now, put yourself back in the suit. The fabric is going to exert pressure on your body because the gas inside has compressed and the suit wants to occupy a smaller volume.

I can't believe a thread on such a simple concept has gone on for 6 pages!

 

[Thalassamania]

Did we all just forget about Boyle's law when we put on drysuits?!

Apparently the balloon analogy was missed by some.

Picture your drysuit, sealed up, pumped with air and sealed at the neck and wrists. You are not in your drysuit.

Now bring just the suit down to 100 ft. The gas inside the suit will compess to roughly 1/4 the volume that it was on the surface. The suit, because it is made out of flexible fabric, will fold and crumple in order to accommodate the reduced volume inside.

Now, put yourself back in the suit. The fabric is going to exert pressure on your body because the gas inside has compressed and the suit wants to occupy a smaller volume.

I can't believe a thread on such a simple concept has gone on for 6 pages!

I think people get the concept, the problem is with "squeezing" the English language arround it.

 

[ReefHound]

A wet suit is made to comform to the shape of the body to miniminize water movement out of the suit. Because of that, any force outside of it is transduced evenly in an inwards direction.

A dry suit is made larger on purpose to provide space for air/undies.

So.. by design, the pressure on dry suit is not being applied evenly in a normal (the physics definition of normal) direction to the surface of your skin. Because of the extra flaps of material, the suit pinches and applies force irregularly and shears your skin. It pulls and tugs on it laterally more than a wet suit would.

View attachment 37215

= ouchie

This has been my prevailing theory, thus why I mentioned Pascal earlier. Water distributes the pressures uniformly so while you have compression of skin you don't have stretching of skin.

 

[ReefHound]

Does the amount of air in a tied off balloon with no leaks change as I squish it around? There is no need for a container to be rigid for it to have constant volume.

What you mean to say is that a flexible container is subject to pressure changes; whereas a rigid one is not.

Pressure and volume, though related intimately in diving, are not the same concept.

Neither are mass and volume the same concept. While the amount of air (mass) in the balloon doesn't change, the volume certainly does. Just take one down to depth and watch it grow smaller. Let me modify to say a container must be rigid to maintain volume when exposed to uniform differential pressure.

 

[ReefHound]

After reading some of the comments on this thread, I'm not sure if the problem is caused by the air in the suit getting compressed or that air pockets in the suit allow the pressure to be felt unevenly. Basically the spots where there isn't air are felt as a hard surface while the places where there is air between you and the suit are felt as a soft surface.

No, it's not a sensory illusion caused by different sensations, it is a real effect. People get bruised and sore from it.