[PSUBS-MAILIST] motor oil compensator

Wed Mar 25 17:36:56 EDT 2020

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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