Question Function dump valve drysuite

[Kofferfisch]

Hello together,

till now I thought the dump valve is basicly an overpreassure valve. But for some time I think how is the overpreasure generated? In my understanding the preasure inside of the dry suite is equal to the ambient pressure because the suite have no solid structure. If i change depth (preasure) the volume of the dry suite changes (p*V=const.).

This get me thinking if the inside preasure = ambient preasure how the valve opens?

Greetings Joachim

 

[Jersey1971]

Imagine a ziplock bag containing an air bubble attached to a weight to achieve neutral buoyancy. The top of the bag will be subject to an upward buoyancy force from the air bubble equal to the negative buoyancy force exerted by the weight.

Now if you open a vent at the top of the bag, air will bubble out. That’s the equivalent to a dump valve all the way open. You can adjust the valve to provide resistance against the air exiting to prevent the gas exiting. Or you can swivel the bag so the vent is below the level of the air bubble. That will also prevent gas exit.

 

[Kofferfisch]

Imagine a ziplock bag containing an air bubble attached to a weight to achieve neutral buoyancy. The top of the bag will be subject to an upward buoyancy force from the air bubble equal to the negative buoyancy force exerted by the weight.

Now if you open a vent at the top of the bag, air will bubble out. That’s the equivalent to a dump valve all the way open. You can adjust the valve to provide resistance against the air exiting to prevent the gas exiting. Or you can swivel the bag so the vent is below the level of the air bubble. That will also prevent gas exit.

Basicly i know what a Dumpvalve do. What Im interested in is the technical princip how this is working.

Maybe I should more specific "How does the automatic opening of the dump valve work?"

 

[rhwestfall]

A variable force spring holds the valve closed...

 

[Kofferfisch]

A variable force spring holds the valve closed...

Then it is an overpreasure valve?

 

[rhwestfall]

 

[Kofferfisch]

This video i already saw. But i think i does not answer the question or i do not understand it. But it got me thinking. If preasure inside the suite = ambient preasure then only the buoyancy force of the air itself could open the valve.

 

[rjack321]

This video i already saw. But i think i does not answer the question or i do not understand it. But it got me thinking. If preasure inside the suite = ambient preasure then only the buoyancy force of the air itself could open the valve.

The suit pressure is not evenly distributed "ambient" is not the same at your feet and your head (if you were standing for instance). If you drop your legs the water squeezes that gas towards your head - and it vents. If you roll your shoulder the valve is at the top and the water pushes the gas from your chest to the highest point and it vents. The spring is not especially strong and depending on if it's turned up or down 10 to 70cm of pressure difference is enough to vent.

 

[Kofferfisch]

Yes preasure is not even ditributed which im aware of. When the air is "transferd" to a different, for example a higher position, in the suit the volume is expanding (p*V=const). So no overpreasure is generated if i dive with a "normal" filled suite. Which force opens the valve when at the valve is no preasuredifference. Because to get a preasure difference the suite must be filled like a baloon in my oppinion.

 

[Barefoot_Lawyer]

Yes preasure is not even ditributed which im aware of. When the air is "transferd" to a different, for example a higher position, in the suit the volume is expanding (p*V=const). So no overpreasure is generated if i dive with a "normal" filled suite. Which force opens the valve when at the valve is no preasuredifference. Because to get a preasure difference the suite must be filled like a baloon in my oppinion.

My conceptualization of the force differential that causes the dump valve to open is the buoyancy of the air. I would think of this force in terms of a vector force (air wants to go up to the surface) and not difference in scalar force (atmospheres / BAR). But it’s been about 25 years since I took physics.