[PSUBS-MAILIST] Motor modification

Mon Dec 5 17:58:00 EST 2016

The things that can cause a change in the required compensation volume are:

1) Any existing gas bubbles shrinking or expanding with pressure change
2) Volume change of the housing, of the oil, or of the motor itself (windings, shaft, bearings, etc.) due to change in temperature of any of these
3) Pumping action of the shaft seals due to the geometry at the seal lip, which can drive small amounts of fluid in or out of the system in proportion to shaft speed, and
4) other leaks.

In short, going entirely uncompensated is not wise (unless your shaft seals have been proven to withstand a pressure differential equal to the pressure at the operating depth), because any entrained air which shrinks, temperature change, or seal lip pumping will generate a delta-P across the seals, and if it is negative, any leakage across the seal will admit sea (or lake, etc.) water to the enclosure.  Adding non biased compensation reduces the delta-P across the seal to zero, but that doesn't mean it won't leak because the dynamic seal lip pumping can still be a problem.  Adding bias to the compensation (air pressure, spring pressure, preloaded elastic bladder, etc.) ensures that the delta-P is positive, so that any leak that does occur will be outward rather than inward, and furthermore, gives you a condition monitoring tool in the form of the bladder volume, since you can tell if the reservoir volume has been consumed that you have had a leak.

Sean

On December 5, 2016 3:04:54 PM MST, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Alan,
>
>I am confused (which doesn't take much) but you talk about doing a test
>to
>collapse a PVC hose. I assume that the hose leads from an oil filled
>vessel
>to a bladder both being completely filled with a dielectric fluid/oil.
>So I
>was thinking that the hose and bladder were to allow for slight
>expansion
>as the oil warms up from use so that the factory prop shaft 0 rings
>would
>not be extruded outward from excess pressure?. This is based on there
>being
>NO air in the vessel, hose or bladder. I didn't realize that there were
>two
>0 rings on the Minn-Kota prop shaft so I do see what you are saying
>about
>the outer most 0 ring pushing in with increased pressure. The way I
>understand it though is if you have ANY air in the system than you are
>defeating the purpose of having a hose and bladder, correct?
>
>Rick
>
>On Mon, Dec 5, 2016 at 11:03 AM, Alan James via Personal_Submersibles <
>personal_submersibles at psubs.org> wrote:
>
>> Some compensating thoughts.
>> On James Cameron's sub they used IV drip bags. I am not sure what
>they
>> were compensating.
>> These come with various means of hose attachment.
>>    With regard to the wrap around hose method; I did some
>calculations on
>> a standard pvc hose, & surprisingly
>> the colapse pressure was around 100psi. I am sure one of Nuytco's
>> technicians told me they crimped the hose
>> that was compensating their lights, to initiate the collapse of the
>hose
>> for compensation.
>>    The industry standard for thrusters seems to be around 4psi
>internal
>> overpressure,
>> but the compensators they use for this are relatively expensive. Hugh
>came
>> up with
>> the novel idea of using a releiving regulator set at 4psi (Parker
>PR364).
>> Cliff is using this.
>> This could be used for air or oil compensation.
>>    The seals need oil for lubrication, & I have read that they can
>use
>> about a teaspoon a day. Based
>> on that I would have some sort of reservoir.
>>    Depending on the motor it may be tricky to get all the air out. If
>you
>> have a bearing in a bore
>> followed by a seal, the air / oil would have to move through the
>bearing
>> which may be a sealed type
>> or packed with grease. The Minn kotta diagrams I have seen show 2
>seals;
>> so how do you get oil or
>> ambient pressure between those? One will fail when you exceed it's
>> pressure limit.
>> Alan
>>
>>
>> ------------------------------
>> *From:* James Frankland via Personal_Submersibles <
>> personal_submersibles at psubs.org>
>> *To:* Personal Submersibles General Discussion <
>> personal_submersibles at psubs.org>
>> *Sent:* Tuesday, December 6, 2016 4:44 AM
>> *Subject:* Re: [PSUBS-MAILIST] Motor modification
>>
>> Hi Antoine\Hank.
>>
>> Thanks guys.  drinking bladder looks good.  I was thinking of a
>furniture
>> lift bag, which is very similar.  I use a hot water bottle for the
>aft
>> motor.
>>
>> Hank, what do you use for a bladder?
>>
>> Thanks
>> James
>>
>> On 5 December 2016 at 13:18, hank pronk via Personal_Submersibles <
>> personal_submersibles at psubs.org> wrote:
>>
>> James,
>> I put my fill plug under the prop, in the flat end cap,  and it works
>like
>> a dream.
>> Hank
>>
>>
>> On Monday, December 5, 2016 5:37 AM, Antoine Delafargue via
>> Personal_Submersibles <personal_submersibles at psubs. org
>> <personal_submersibles at psubs.org>> wrote:
>>
>>
>> Hi frank
>> I have done something like that for my prop shaft seal oil filled
>> compartment.  But first i removed the hose and filled with a serynge
>with
>> long steel needle. Then put the tube and filled it with the serynge.
>> The tube is flexible and transparent, from endurance sport
>> platypus drinking bladder
>> Works well
>> Regards
>> Antoine
>> On Monday, December 5, 2016, James Frankland via
>Personal_Submersibles <personal_submersibles at psubs.
>> org <personal_submersibles at psubs.org>> wrote:
>>
>> Hi All
>>
>> I have been talking to Rick about motor compensation which has got me
>> thinking.
>>
>> I originally did my motors like other psubbers have done with the
>rubber
>> tubes around the sides, but have found them a real pain to fill. 
>Problem
>> is the location of the tube, plus the tiny bit of protruding pipe
>nipple on
>> the inside.
>>
>> So, I modified the motors by drilling a hole in the top part of the
>> aluminium endcap and use that now as the vent\final fill.  Its
>better, but
>> still awkward.
>>
>> I have suggested to Rick this idea, which I am tempted to adopt
>myself.
>> Blocking off the existing side mounted pipe nipples and
>> filling\venting\compensating all from the one top hole.  There would
>be a
>> rubber bulb of some sort on the end of the pipe.  2x pictures show
>filling
>> and operation.  Appologies for rubbish drawings, im at work.
>>
>> What does everyone think?
>>
>>
>> 
>> 
>>
>>
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