[PSUBS-MAILIST] motor oil compensator

Wed Mar 25 15:32:00 EDT 2020

 Brian,
I have a pressure compensation calculator on the website.  Enter max depth, length of your tube, and it will tell you the air gap at that depth (seawater).   PSUBS.ORG

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    On Wednesday, March 25, 2020, 11:17:07 AM EDT, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Alan,          Yes I did think about that condition ,  the drawback with having a large reservoir is that there is that much more air to compress.  I was going to have a plug in the bottom of the 3" pvc so I could drain it out if I did get some water in there or if there was water and oil.  What I need to do is to just calculate the total volume of air and see how much water would fill the reservoir at maximum depth.   As long as the reservoir does not completely fill then there's no way water can get to the motor.  Theoretically you could squeeze the air down to nothing in the reservoir.     
Hank,   oh the stories I could tell you about transferring honey ( listen David !)  pouring  55 gallons of cold honey into a 5 gallon pail,  not being one who wants to waist time, I couldn't just sit there doing nothing for a half an hour so I naturally found a small project to do .  Then getting involved with what ever I was doing  -  you can guess the rest   , honey is very quiet when it's draining all over your shop floor 55 gallons into every nook and cranny you can imagine !     unfortunately this happened more than once  !   

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 21:42:08 +1300

Brian,not sure of your depth but if you are going to 300ft, the air will be compressed to1/12th the volume, so the oil overflow reservoir is going to be problematic becauseIt's large volume could mean the seawater would come a long way up the tube onthe 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 usinga 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 whenthe motor is under load it will be drawing a lot more amps & develop alot 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.pdfI printed it out & had it bound.I found that the rotation of the motor was throwing the oil out of the motorhousing & up in to the compensating tube. If you dived there would be addedpressure to keep the oil in the motor housing, but this wouldn't happen transitingon the surface. As the oil also keeps the Motor cool, there may be a danger ofthe 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 dialledup 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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