Andy:
At 600' down, the external pressure will be an additional 18 atmospheres squeezing the innertube. You're not going to be able to find any hand pump that can handle that tremendous pressure.
To get an idea of how much force you would be working with, imagine having a hollow square tube that is welded through the hull of your sub. The inside of this square tube is exactly one inch high, by one inch wide. Now, you have a square steel rod that is exactly one inch wide, by one inch high, and it's the exact same length as the tube. Before you put your sub in the water, you put the rod into the tube.
Now, you start descending into the depths of the ocean. The pressure of the water starts to push the rod into your sub! You grab the rod and push it back. At 33 feet down, the rod is pushing against your hand with a force of 14.7 pounds. At 66 feet, it's pushing with a force of 29.4 pounds. When you reach 600 feet, that same rod is pushing against your hand with over 267 pounds of force! (I hope you're alot stronger than I am!!)
Now...that's just one square inch of surface area. How much surface area is on a truck innertube?
I'm sorry Andy, there's just no way you can generate that kind of pressure with a small electric pump, or a hand pump.
-- NP
From: Andy Jensen <drewacard@charter.net>
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
CC: ShellyDalg@aol.com
Subject: Re: [PSUBS-MAILIST] RE: payload
Date: Tue, 5 Dec 2006 7:37:11 -0800
>I was thinking about using an oil kept in side the sub and pumping it into an expandable bladder out side the sub using either an electric or hand hydraulic pump.
>
>one through hull and one valve. A truck inner tube in a small thin tank open tank.
>using water to force the oil back in. Most hydraulic connections are rated at 3000PSI working pressure should give me plenty of over head for 600'.
>
>It seems to simple so what am I missing?
>
>Andy J.
>
>
>
>---- ShellyDalg@aol.com wrote:
>Kory. I have always thought trim tanks were to adjust trim, not compensate
>for varying loads.
>Water density changes with temperature and salinity, but not very much. It
>is possible to run into a salty current or water layer and trim can be added or
> reduced to compensate.
>Sometimes subs have forward and aft trim tanks to change the angle of the
>sub while still maintaining neutral buoyancy.
>Adding lead ballast before a dive, depending on load, is easier than having
>a separate, large system with associated piping and tanks which requires
>maintenance, cost, and monitoring.
>With a few dives, you know how much added weight your sub needs to reach
>neutral, and then you adjust with weights from there for added passengers,
>cargo, new equipment, or whatever.
>Trim tanks need to be at one atmosphere, whether full or empty.
>Ballast tanks are ambient.
>If your trim tank is half full and open to the sea, ( like a ballast tank )
>the air will compress when you get deeper, and you'll start sinking fast.
>Large, one atmosphere tanks for trim will require heavy walled tanks, fill
>valves, drain valves, pressure monitoring, and take up room and add weight
>because they're thick steel.
>And you have to flush them out after every dive so they don't corrode.
>Better to have small tanks for trim and carry some lead.
>Just my opinion....Frank D.
>
>
>
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