[PSUBS-MAILIST] motor oil compensator
Alan via Personal_Submersibles
personal_submersibles at psubs.org
Wed Mar 25 19:58:01 EDT 2020
Rick,
they were using IV bags on James Cameron's sub.
I am not sure what they were compensating with them, but they have
attachment points for hoses which are handy.
Alan
> On 25/03/2020, at 9:08 PM, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> I am oil compensating but haven't done the motors yet. I have talked to a couple people who haven't added bladders for the hot oil to go and said that they haven't had a problem but I have all ready drilled and tapped 2 holes in each thruster so gonna do it. I saw some that did what you did James but couldn't see how the short run of hose would allow any expansion so I found some small plastic bags like the ones that hospitals use to drip saline and other stuff into your blood system. I liked these as they are a lot smaller and were meant for a Halloween gag so gonna have a short hose that goes to each bag which will be wire tied to each thruster.
> Rick
>
>> On Wed, Mar 25, 2020 at 11:38 AM 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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>>>>> Personal_Submersibles at psubs.org
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>>>>>
>>>>>
>>>>> --
>>>>> Vennlig hilsen
>>>>> Øystein Skarholm
>>>>> 91369599
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