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sponges can be cleaned and reused............it's not like it a one-time use and throw away. do you throw away your clothes if they get dirt and buy new ones?
OK I have to ask.
What did the slaves (presumably) who cleaned the sponges wash their hands with?
Did they use "Pre-Owned" ones they'd washed?
 

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I'm fortunate.
Sea level & water table is -7'.
I can hand pump with a lift pump if I have to, I don't even need a force pump.
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Big Coulee.
Have you ever heard of a "bubble pump"?
They're neat but a bit uncommon.
Basically you run small-bore pipe down inside a larger pipe.
At the top is basically a bicycle pump.
What you do is pump high pressure air down through the small bore pipe to the bottom of the full-bore pipe till fluid exits at first & wait a few seconds then pump again, one stroke at a time.
If you have a check valve at the surface you don't need the initial pressurization.
The "pulsed" bubbles exit under pressure matching the head pressure & expand as they rise, lifting the water column with them. You can aslo use an air compressor using short "puffs" if you have one.
The advantage is the pause between pumps so the operator can pump longer, because its less tiring & the mechanics are all at the surface.
Its also depth independent up to the level of the air pumps pressure ability.
 

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I'm not sure of the depth limit but I've seen SCUBA divers using it in 120' of sea water with no problems.
The trick is intermittent air pulsed, each bubble is only lifting the column between bubbles regardless of depth. The gas expansion (2X per 33 or 34') helps too.
If i used a compressor I'd use a small intermediate cylindrical to control bubble size.If you've seen the movie of "For Your Eyes Only", the Greek archaeologist "Melina Havelock", is using a very large one in the "underwater temple" scene.
 

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Yes exactly.
But it would also depend on time.
60' for 60" is the decom limits, after that you get into decompression tables (the dreaded "Bends")
The usual formula is 1 Atm (14.7 PSI per atm. per 33' (or 34' for fresh) water.
Double or more the RNT (Retained Nitrogen) + the current Nitrogen loading, & you're into decom.
That's why Tektite 1 was at 31' BSL. You can saturate all the tissue groups & you still won't "bend".
This is based on the U.S. Navy dive table & has a 10% error factor.
For superbly fit Navy Seals.
For the purpose of a pump it means nothing, because "The Bends" is retained Nitrogen, not total pressure. But gives good well researched idea of compression per foot.
One thing they do when you're training for SCUBA is to take a blown up balloon with you it shrinks as it pressurizes to ambient. At 60' its one quarter (more or less) of its surface volume.
Then you exhale one breath into a different balloon at depth & watch as you come up.
It frequently bursts.

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Not at all, it works perfectly for both.
The surface hand-pumped one is conciderably smaller though, but it will deliver a considerable volume of water easily from a substantial depth.
 
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