[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Mon Jun 8 17:16:34 EDT 2015

Alec,
I have the same problem with my drive on Gamma, when returning to the surface the shaft tube is under pressure.  I have a ball valve mounted to the tube and even a month later there is pressure until I open the ball valve.  I have tried a softer compensation bladder with no luck.  There has to be an air pocket that we are not getting rid of.  Brian's suggestion is not bad at all, forget the bladder and rig an open hose with traps so the oil can not escape.  There would be an air space trapped between the oil and water in the length of tube.  That air bubble would simply move in two directions depending on depth.  A very simple solution, more tricky for you because your motors rotate.  I think I will test this idea since I have my tail assembly off for repairs anyways.
Hank--------------------------------------------
On Mon, 6/8/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Monday, June 8, 2015, 4:48 PM

 OK, let me
 try to reason this through again. Lets say the standard
 trolling motor shaft seal is watertight to 50 feet, and that
 initially I had 1 cubic inch of bubble in the system. Dive
 to 250 feet and what I would have thought would happen is
 that the 1 cubic inch of air would be reduced to 1/8th in3
 due to 8 atmospheres of pressure increase. I would have
 expected that the compensation bladder would have just been
 squeezed by that volume, and that upon surfacing the bubble
 would go back to 1 in3 and the pressure in the motor to 1
 atm. However, what we found was that the motor upon
 surfacing was significantly pressurized. The compensation
 bladder (i.e. hose) was visibly distended by internal
 pressure upon surfacing. There was no leak at the hose
 clamps, but oil was leaking from the shaft seal.
 Since there was over-pressure
 surfaced, clearly water had to have entered the system
 during the dive, and as the hose clamps were leak free and
 the seal was not, I suspect the seal. Now the question is
 why water would get in. Bubble greater than the compression
 range of the hose? Seal offering less resistance than the
 hose to compression? Shaft pumping water under the seal
 during operation due to abrasions? Thermal contraction?
 I'm actually not sure - any theories are welcome. One
 interesting detail - the stern thruster, which was not
 working due to the issue with the speed controller, did not
 have any oil leaks. Both side thrusters, operating,
 did.
 The side
 thrusters being feeble can be explained by pressure on their
 seals, or just by their age and related wear on the
 commutators. I will be changing them, or at least their
 internals.

 Best,
 Alec 
 On Mon, Jun 8, 2015 at 2:54
 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
 wrote:

       It sounds like at some point water pressure at the
 seal was able
       to compress the bubble of air in the tube, the
 opposite of what
       was expected.

       I'm kind of stumped by the description of the
 motors performance
       being "feeble" however.  This couldn't
 have been primarily due to
       pressure I don't think.  Also, isn't an easy
 fix just to "clamp"
       the tube any place where liquid appears assuming the
 tube is held
       in a vertical position and the bubble is at the top
 (ie vise grip
       the tube).

       Jon

       On 6/8/2015 12:01 PM, Brian Cox via
 Personal_Submersibles wrote:

         Hmm, guess I'm not getting what is
 happening

         Brian

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