[PSUBS-MAILIST] motor oil compensator

Wed Mar 25 08:35:09 EDT 2020

Hi All,
This is a really interesting topic for me.  I have been meaning to ask this
for a while but been a bit busy with other stuff.
I need to modify my motors again somehow.  I have a simple tube coming from
the top of the motor with a valve that i can shut, so i can seal the motor
and close it off.

No matter what i do, i always seem to end up with a small amount of air in
the tube.

This picture is the only one i can find.

The tube comes out the top, around to a valve secured underneath.  Thats
it.  There is no hole on the underside any more.

I fill it, it seems fine.  The next day there are a few bubbles, which i
would expect from just sticking to things.  So i clear that.  However,
after either a dive or some time, a small amount of air gets in the tube.

There appears to be no leaks and no seawater in the motor.

What am i doing wrong?  Its such a nuisance and worry to me.

I have heard that some people put the prop shaft seals in backwards?  I
didnt do that, they are just standard.

I suspect im getting pressure differences and its sucking air past the
seal.  Maybe some sort of 5 psi pressure system is required, as per cliffs
method?  Any more info on that?

Thanks,
James

[image: image.png]

On Wed, 25 Mar 2020 at 08:43, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> 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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