[PSUBS-MAILIST] Motor modification

Wed Dec 7 17:11:12 EST 2016

Rick - if all you have is the tube (i.e. no separate bladder), then if you fill it completely, any additional oil has no place to go unless the tube wall stretches. Similarly, most tubes with any rigidity at all resist collapse due to external pressure, so if you have an air bubble within the housing that shrinks and demands compensation oil, the tube won't necessarily deliver it unless it is able to collapse - meaning either it has to be flimsy, or you have to crimp or bend it in order to initiate the collapse, so that the collapse can propagate down the remainder of the tube length in order to lose volume.  Ideally, your compensation reservoir is filled to an intermediate volume that can either accept or deliver oil as demanded.  Keep in mind that as your motor heats up, the oil will heat up and expand, but then the housing will heat up and increase volume, drawing back some of that oil. A good compensation system has some capacity in both directions. The comment about lights was
that wiring can be run through oil filled tubes in order to pressure compensate the light housings, but this can suffer from the same problem - clear PVC tubing is a lot stronger than you might think, and you need to help it along with a crimp, otherwise external pressure may stress the tubing but not actually compress it. Personally, I am a fan of rigid plumbing to a remote non rigid oil reservoir (which may be pressure biased or not, depending on the application), but I know that doesn't work for everybody.  Bubbles aren't a huge deal, as long as you have enough compensation oil available to accommodate the volume change due to pressure. Obviously you should vent as much air as you can out of the system.

Sean

On December 7, 2016 2:38:16 PM MST, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Alan,
>
>I am embarrassed to say that I am still not getting this concept. You
>mentioned in your email about the clear hose that people wrap around
>there
>Minn-Kota motors and mention about collapse pressure and also mention
>about
>lighting systems. Maybe we are talking about two separate things?
>My question was based on wondering about that same clear tubing that
>wraps
>around the motor pods to allow for when the oil gets hot from use and
>expands.
>Taking any air out of the equation, I got the impression that you could
>completely fill a motor with dielectric oil (or any liquid for that
>matter)
>and then take it to any depth and since you basically can't compress a
>liquid, there would be no water ingress to the motor (except for the
>small
>space between the two prop shaft 0 rings.) So now when you add a slight
>internal increase in pressure from the oil being heated from use,
>people
>use the clear tubing that wraps around the outside of the motor (which
>is
>also 100% filled with the same oil) as a place for the oil to go to
>expand
>rather that spitting out the prop shaft 0 rings. Am I correct so far?
>So my question was, the clear hose wall must be flexible enough to
>allow
>for expansion before placing enough pressure on the prop shaft 0 ring
>to
>dislodge? And then if you don't get all the air out of the motor or
>clear
>hose or bladder, don't you have the water pressure trying to compress
>that
>bubble from not only the bladder or tube but past the shaft 0 ring as
>well?
>
>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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