[PSUBS-MAILIST] motor oil compensator

Thu Mar 26 13:14:41 EDT 2020

Also interested in Cliff's compensator regulator that was mentioned.  Any
info on that.

Many thanks

On Thu, 26 Mar 2020 at 17:08, James Frankland <jamesf at guernseysubmarine.com>
wrote:

> 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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