[PSUBS-MAILIST] FW: VBT pump

Wed Aug 16 12:54:41 EDT 2023

 It's all about the usage. A VBT was handy when working a PC12 (for instance) mid-water or alongside some kind of structure.  That said, I ran Aquarius quite successfully using the forward (smallest of 3) MBT to hang on the bubble, as we called it. You have to be quick on the adjustments, but it worked fine that way. The JSLs have a dandy pressure compensated system for the VBTs, but you may notice how many T bottles are hung on those things. They were air hungry by definition. The little boats we mess with respond much more quickly to the bubble trim, but smaller volumes of air are involved, so are reasonably manageable. The Nektons, for instnce, ran on the bubble and fit into our sort of portable category (4400 to 5200 pounds crane weight). An 8 to 10 ton Perry or Hyco sub, however, is much happier trimmed neutral, or very close to it. In relatively shallow water (call it down to 500 feet or so) I could easily run those subs a little heavy, and then fine trim with the MBT bubble. Not always, but it was nice to have the options.Vance
    On Wednesday, August 16, 2023, 09:30:02 AM EDT, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  Hugh, on my original design for the R300 I had a hard VBT just aft of the pilot. At the time I had a small HPU in the boat.  My plan was to use a Oberdorfer Bronze gear pump driven by a small hydraulic motor to move water in and out of the VBT.  I don't remember the specs on the pump.  I had motorized ball valves on the vent and flood side of the VBT.  Prior to using this set up, I did some testing of this gear pump which I still have.  What I found was an unacceptable amount of flow slippage at my max design depth.  There was so much slippage that the pump could not blow the VBT at max depth.  At that point I abandoned using a pump and vent to blowing the VBT with air.  I eventually abandoned the VBT altogether for operability reasons.  When I used this hard VBT to get neutral on the surface, the pressure in the tank was low.  When at depth if I ever tried to use the VBT, water would rush in until the pressure equalized with ambient water pressure.  This made the boat negatively buoyant until air was added.  The other thing that bugged me was I had a float style level sensor in the VBT.  The water level in the VBT was always moving around so you never trust the reading.  I eventually abandoned the VBT and now just add ballast at the boat CG where the VBT was located.  I find this works great.  The other issue is the VBT restricted access to equipment aft of the VBT so to work on any of this equipment, I had to remove the VBT.   All in all, I found the VBT to be a pain in butt.
Cliff
Oberdorfer 944 Bronze

    On Sunday, August 13, 2023 at 04:57:24 PM CDT, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

Hi Guys

What make of pump is best for VBT water transfer in/out for 250 psi 1.5 kw.

I am looking at a gear pump 1.5kw Oberdorfer 944 Bronze.  These are only rated for 10 bar.  I tried an hydraulic gear pump 30cc where I had a stainless and bronze gear set made up but the aluminium body corroded form the trials and I just found that they had used steel backed sleeve bearings.

Regards,

Hugh 
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