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At 05:28 02.02.98 -0600, you wrote:
>I'm considering fitting dump valves to my membrane suit about 8 inches above
>each heel.
>This seems like a good idea to minimise the risk of an inverted buoyant
>ascent,
>and if they leak it's no big deal.
>Can anyone tell me if this is a stupid idea, or have experience of similar
>setups.
>
>Regards and thanks in advance - Ewan

My feeling is, if you need dumps at the ankles you'd be better off
practicing diving the suit. By the same token, people who feel they need
ankle weights usually change their mind after some dives. 

How would you avoid an inverted buoyant ascent? You'd want to crouch and
pull your knees up towards your chest. Once you're "rolled up" it's easy to
re-assume position. There will be an initial minor ascent as you "roll up".
However, what doesn't work is to try to fight a buoyant ascent by swimming
down. The legs are full of air, and this air will stay there until you
invert your position. Since you can't swim your legs down, you'll have to
raise your upper body to the same level to be able to pull your knees up and
displace suit gas to upper body. That's when you dump the excess. Once you
get used to the gas displacement you'll learn to recognize the signs and
arrest the problem before it progresses.

If your suit air displacement becomes second nature you may even appreciate
it in that it provides a means of shifting gas where you want it. If your
feet get cold a controlled displacement rushes warm gas into your socks.
With ankle dumps you'd lose gas the moment you try to take the squeeze off
of your booties. Ankle dumps are also more prone to leak since your feet
will be at negative to zero pressure most of the time while a dump on upper
body will tend to experience positive pressure from inside most of the time.
This means that the valve diaphragm will tend to flutter around zero. Put
differently, with an imperfect seal an upper body dump will cause gas to
trickle out while an ankle dump will cause water to trickle in.

regards

Hans   

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