[PSUBS-MAILIST] RE VBT Pump.

Wed Aug 16 19:43:53 EDT 2023

Hi Vance, Cliff,  Thanks for the feedback.  Correction of the pump I am
looking at it is an Oberdorfer 994 but also comparing a piston diaphragm.
Vance experience looks as though it was much deeper than the 50-400 ft I am
looking at with the NZ coastline.  150 feet is the max in most places with
coastal access. 

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Subject: Personal_Submersibles Digest, Vol 120, Issue 38

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Today's Topics:

   1. Re: FW: VBT pump (vbra676539 at aol.com via Personal_Submersibles)
   2. Re: FW: VBT pump (hank pronk via Personal_Submersibles)
   3. Re: FW: VBT pump (Rick Patton via Personal_Submersibles)

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Message: 1
Date: Wed, 16 Aug 2023 16:54:41 +0000 (UTC)
From: "vbra676539 at aol.com via Personal_Submersibles"
	<personal_submersibles at psubs.org>
To: Cliff Redus via Personal_Submersibles
	<personal_submersibles at psubs.org>
Subject: Re: [PSUBS-MAILIST] FW: VBT pump
Message-ID: <886051092.283168.1692204881545 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

 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 neg!
 atively 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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