[PSUBS-MAILIST] motor oil compensator

Wed Mar 25 04:42:08 EDT 2020

Brian,
not sure of your depth but if you are going to 300ft, the air will be compressed to
1/12th the volume, so the oil overflow reservoir is going to be problematic because
It's large volume could mean the seawater would come a long way up the tube on
the seaward side. Also using it as an overflow would create the problem of "how do 
I get the oil back in the motor" & " how do I monitor it".
I have had rubber perish in WD40 so I would watch that if you are considering using
a rubber compensator.
Have a look at the PDF I referenced as that has several options.
Alan

> On 25/03/2020, at 5:40 PM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Alan, 
>                So do you see any issues with the way I have my compensator set up?   I've been trying to see a scenario where it wouldn't work, but I don't see one.  One reason I like it is because there in no over or under pressure in the system.
> 
> Brian
> 
>   
> 
> --- personal_submersibles at psubs.org wrote:
> 
> From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] motor oil compensator
> Date: Wed, 25 Mar 2020 17:28:21 +1300
> 
> Brian,
> I wouldn't read a lot in to that experiment as far as heating goes, as when
> the motor is under load it will be drawing a lot more amps & develop a
> lot more heat.
> But people run the Minnkotas with air compensation & get away with it.
> Alan
> 
> 
> On 25/03/2020, at 2:09 PM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
>  Alan,  
>                    In my case my motor pod contains about 8 gallons of WD40   .  I ran the motors the other day , all day long for about 10 hours straight .  The temp outside was around 60 F  so it sort of simulated our water temperature here.   I was surprised to discover that the expansion of the oil was not as much as I thought it would be , it was about 1/2 gallon.  It reached a point where it stopped expanding, so I guess it reached a point of equilibrium with respect to the temperature.    One problem I have is in the summer the oil actually expands more than when the motor is running just sitting there heating up from the ambient temperature.    I think in the summer I'm going to disconnect the hose and put it into a bucket when sitting.  
> 
> Brian
> 
>  
> 
> --- personal_submersibles at psubs.org wrote:
> 
> From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] motor oil compensator
> Date: Wed, 25 Mar 2020 13:25:53 +1300
> 
> Brian,
> there is this military de-classified 1972 document on pressure compensating.
> https://apps.dtic.mil/dtic/tr/fulltext/u2/894795.pdf
> I printed it out & had it bound.
> I found that the rotation of the motor was throwing the oil out of the motor
> housing & up in to the compensating tube. If you dived there would be added
> pressure to keep the oil in the motor housing, but this wouldn't happen transiting
> on the surface. As the oil also keeps the Motor cool, there may be a danger of
> the motor overheating in this instance.
> As you will find in the linked manual, a minimum of 5psi over pressure is the norm.
> I am going to use the same system as Cliff, with the relieving regulator dialled
> up to 5psi to give an overpressure. However my system has oil in it so I get it's 
> cooling advantages & eliminate large air volume changes.
> Alan
> 
> On 25/03/2020, at 11:19 AM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Seawater gets compressed up the hose, so never goes above the highest point of the hose.  When oil heats up it spills into trap and cannot escape to the sea. 
> 
> Brian
> 
> 
> --- personal_submersibles at psubs.org wrote:
> 
> From: Øystein Skarholm via Personal_Submersibles <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] motor oil compensator
> Date: Tue, 24 Mar 2020 22:21:15 +0100
> 
> You should avoid contact between the seawater and the oil. The oil will contaminate quickly and it will no longer be dielectric. 
> Just the hose from the motor to the tee is enough to compensate. You do not have to have a large volume of oil. Fill the hose with oil and cap it off, done. or make a neat yet more sophisticated solution. 
> Make the end lid of the motor as a flange assembly and instead of a lid, use a rubber diaphragm. This will then act as a compensator. You can even install a light spring pushing down on the diaphragm  if you want a slight internal overpressure. 
> <image.png>
> 
> tir. 24. mar. 2020 kl. 21:28 skrev Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org>:
> Here is a drawing for my oil compensator
> 
> 
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> 
> -- 
> Vennlig hilsen
> Øystein Skarholm
> 91369599
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