Re: [PSUBS-MAILIST] Main ballast.

[Ray Keefer <Ray.Keefer@Sun.COM>]

Hi Pierre,

Assuming we are talking about a soft ballast tank.

A soft tank is one that is strong enough to work at near ambient pressure
differentials. The main ballast tank is either completely full of water
or completely full of air. Which ever is in it, the main ballast tank is at
ambient (or near ambient) pressures. This kind of main ballast tank
is never used to adjust bouyancy by sealing the tank as it is not strong
enough to handle large pressure differentials. It's only purpose is to
supply large amounts of positive bouyancy on the surface. When submerged
the main ballast tank is empty of air and full of water.

An MBT typically only has a valve at the top of the tank to let air
out, a open hole at the bottom to let water freely enter and leave,
and a compressed air line that is valved. To empty the tank of air, or
fill with water, open the top valve. Close valve once all the air has
left. To empty the MBT of water, open the air valve. The compressed air
will force the water out the bottom hole.

To adjust bouyancy use a Variable Ballast Tank. A VBT is a hard ballast
tank. A hard ballast tank has two valves, one on top and one on bottom, 
plus a compressed air line. The construction of the VBT has to be just
as strong as the pressure hull since fine adjustment is done near the surface
but the sub may be operating at several hundred feet down. The air in the
VBT will be at near surface level pressure but the surrounding pressure
is at ambient for that depth.

Now if you really want to use your soft MBT to adjust bouyancy you can,
but you will have to constantly adjust the air in the tank.
As you go deeper the ambient pressure will compress any air in the
MBT. You will have to have some compensating mechanism to let more air
into the MBT to fill it up to some preset level. As you assend the
air will expand. The same mechanism will have to let some of the
expanding air out. Kind of like how the SportSub's main cabin is used.

K-350 uses to soft MBT. One forward and one aft. It also uses a
VBT.

Regards,
Ray 


> Date: Wed, 21 May 2003 18:31:07 -0400
> From: pierre&marie <poulin.carrier@videotron.ca>
> Subject: [PSUBS-MAILIST] Main ballast.
> To: personal_submersibles@psubs.org
> X-MIMEOLE: Produced By Microsoft MimeOLE V5.50.4133.2400
> Content-transfer-encoding: 7BIT
> X-Priority: 3
> X-MSMail-priority: Normal
> 
> Hi People!
> 
> How do you "plug" the main ballast tank to adjust buyoncy (man, that word is
> killing me...)
> 
> I'm trying to figure a way to use a 5/3 pneumatic valve. It would be easy to
> use to adjust bouyancy. But, I can't have the plumbing right at the moment.
> 
> 
> Any advise? Somebody know how it's done in a K-350?
> 
> Thanks!
> 
> Pierre Poulin
> "At last the sun is here!"
> 
>