[PSUBS-MAILIST] motor oil compensator

Thu Mar 26 13:08:21 EDT 2020

Hi Alan,

Im using silicone oil.

I deliberately kinked the hoses for the very reason you say.  I initially
used silicone hose which is much softer and flexible, but it reacted with
the oil and expanded, quite a lot.

I think I might see if i can get some thinner walled tube (but not
silicone) and wrap it around the motor a couple of times, to give it a
bigger compensator.

Can other people confirm that a small amount of air in the tube is
acceptable?  I have been constantly trying to remove every bubble.  If a
small amount is ok, im pretty good to go.

Also I will be making some progress on my new sub pretty soon.  Just
getting a heavy hoist sorted, which at the moment is difficult as all the
shops are shut.

Regards
James

On Wed, 25 Mar 2020 at 21:38, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> James,
> that method with the hose wrapped around has come under criticism
> previously.
> Fortunately you have a kink in the hose which initiates a collapse of the
> hose to
> provide some equalisation. We calculated that the hose may take over
> 100psi
> external pressure before it collapsed to provide equalisation. So at depth
> water
> would push past the seals before there was any compensation.
> I don't know whether you are still getting trapped air in the system
> coming out
> or whether expansion & contraction when out of the water is sucking air in.
> But for air to get in, oil would have to get out. Maybe oil expands out
> through the
> seals when you transit & it heats up, & then causes a vacuum when you take
> the sub
> out of the water & the motors cool down, thus sucking air in.
> Perhaps you could run the motors out of the water for a while untill they
> feel
> hot, & see if any oil comes out. Another thought is that if you are using
> WD40
> or similar, perhaps it is pushing past the seals with the hot cold
> variation over
> each day, & evaporating away so that there's not much evidence of a leak.
> Alan
>
>
>
> On 26/03/2020, at 1:35 AM, James Frankland via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> 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.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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