Re: [PSUBS-MAILIST] Compressable ballast tanks

Bill, you have it correct; like a water thank in a rural home water supply system.

You could use a hand operated pump to move water in and out of a tank, compressing air as the water goes in, and the same air would be there to decompress and fill the place where the water has been when your pumping out. Of course, you would never be able to completely fill the tank with water but you could easily fill 75% of it.

The same system could be used with a bladder inside the pressure hull. There would be some compression of the air in the hull as you filled the bladder, but to adjust buoyancy with maybe three gallons of water (about 25 pounds) it would hardly be noticed.

You would need a piston type pump capable of over coming the pressure of the depth your diving in. And, maybe a backup pump or carry compressed air to blow your main ballast tanks with just in case of a pump problem.

Dan H.

----- Original Message -----

From: Akins

To: personal_submersibles@psubs.org

Sent: Thursday, January 05, 2006 6:05 AM

Subject: Re: [PSUBS-MAILIST] Compressable ballast tanks

Oops, sorry. I sent that last one accidently before I typed anything.

Hi Dan.

How would I use a small piston pump to move water in or out of the tank without also losing air from the tank? The whole idea is to compress the air, lowering it's volume, then expanding it again for larger volume again.

How could I move water in and out of it without losing air? Unless, what you are describing is something like a home use well bladder tank, wherein the metal tank has a bladder inside it that is air filled and this air filled

bladder gives in to water pressure and has it's bladder body and air, compressed by the water pressure and then the air pressure in the bladder pushes back out against the water. Is this what you meant? Did you mean the

small piston pump would somehow help the bladder push the water out of the tank by allowing the bladder to expand somehow? Or am I totally misunderstanding you? Could you elaborate please Dan?

Thanks, Bill Akins.

----- Original Message -----

From: Dan H.

To: personal_submersibles@psubs.org

Sent: Monday, January 02, 2006 8:11 AM

Subject: Re: [PSUBS-MAILIST] Compressable ballast tanks

Bill,

What you describe sound good in principle. For a SCUBA tank it would way to cumbersome to built it to contain 2000 pound air for the small benefit of not having to adjust your buoyancy in other ways.

For your sub it would be more doable, but still, rather then install a large air tight piston and the mechanism to operate it, wouldn't you get the same result if you operated a simple small piston pump and moved water in or out of a sealed tank? A pump would have a piston, true, but it would be smaller, easier to house and operate. Also one pump can be connected to and operate more then one tank.

Again, your idea is good but there may already be easier ways to accomplish what your after.

A note on the topic: Captain Kittredge is rigging a sub to do what you suggest. He wanted to create a buoyancy system that didn't require compressed air to operate. I believe he's using a hand operated water pump and bladder in his dry sub to pump water into. If you put a bladder in a pod you can do the same thing in your wet sub.

Dan H.