[PSUBS-MAILIST] Yet another compensator method

Tue Jul 7 03:40:50 EDT 2020

Hi All

Thanks for the tips.

Im going to make a slight modification with a T barb fitting to a "valve"
of some sort consisting of a cap to screw in.  Something like that.  Then i
can get most of the air out.

I seem to leak oil somewhere.  I never notice any around, or on the floor,
but air gets in over time.  I think the silicone oil im using is so this,
its difficult to seal.  Ive considered using Marvel mystery oil or even
hydraulic oil.  Any thoughts on that anyone?

Interesting to hear Vance had small amounts of air in after a dive.  Makes
me feel better.  I shall attempt to remove as much as possible, and i do
check\fill the motors before every dive.

Many Thanks,
James

On Mon, 6 Jul 2020 at 18:17, Alec Smyth via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Sorry, my understanding is the exact opposite. Thermal
> expansion/contraction volumes of the oil are significant, but of much
> smaller magnitude than gas volume changes due to pressure if the amount of
> air in the system is not absolutely minimal. Lets say your air bubble was
> half the volume of the bellows, which is about what it looks like in the
> photo. If you go to 350 feet, you will be adding a little more than 10
> atmospheres, so the bubble will only be about a tenth its original volume
> and the bellows will have to contract about 45%. I'm not saying it
> cannot, you might be just fine. But as you dive to your 350 feet, the water
> will also get cold, so the oil will contract too. Quantifying how much
> would depend on the temperature differential and the volume of oil. But my
> point is BOTH the air and the oil are contracting. If their deltas were in
> opposite directions, say with the air contracting and the oil expanding,
> then one could argue an air bubble absorbs the expansion. I did once do the
> math for thermal expansion/contraction on Snoopy's thrusters, and it made
> me switch from just using the coiled length of hose method to adopting what
> looks like the exact same bellows you have in the photo. I selected that
> bellows because it had a volume appropriate to the thermal expansion
> calculation. However, if you add the gas delta to that, I'm not sure the
> math would have still added up.
>
> And yes, filling these things with oil so there's no or minimal bubble is
> a REAL pain!
>
>
> Best,
> Alec
>
> On Mon, Jul 6, 2020 at 10:29 AM James Frankland via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> The air bubble is for a few reasons.
>>
>> 1. To allow easier expansion of the oil if required, even though
>> its enclosed.
>> 2. Seems impossible to completely eliminate it, so thought id go with it.
>> 3.  Some people said you should have a bubble last time i brought this
>> up!
>>
>>
>>
>> On Mon, 6 Jul 2020 at 15:16, Alec Smyth via Personal_Submersibles <
>> personal_submersibles at psubs.org> wrote:
>>
>>> Looks good to me, but why have an air bubble? I always tried like crazy
>>> to eliminate it, since that is what expands or contracts most.
>>>
>>> Thanks,
>>> Alec
>>>
>>> On Mon, Jul 6, 2020 at 10:00 AM hank pronk via Personal_Submersibles <
>>> personal_submersibles at psubs.org> wrote:
>>>
>>>> James, that looks great-the air bubble is good also.
>>>> Hank
>>>>
>>>> On Monday, July 6, 2020, 7:31:46 AM MDT, James Frankland via
>>>> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>>>>
>>>>
>>>> Hi All
>>>>
>>>> Getting Jodie B ready for diving in the next week or so.
>>>> I have changed the motor compensator yet again as the last enclosed one
>>>> didnt really have a proper flexible part and I think the oil expanded a bit
>>>> over time and leaked out through the seals.  Just a tiny bit, but enough to
>>>> put some air back in the pipe.
>>>>
>>>> Anyway, the new method is simply a tube with belows.  These are from a
>>>> toilet flush and have been sitting full of oil for a couple of weeks to see
>>>> if anything happens.  They seem good, so i have installed them. The motor
>>>> is completely filled with oil and the bellows have a small amount of air.
>>>> They compress easily, so should provide pressure compensation while also
>>>> allowing the oil to expand if required.
>>>>
>>>> The bellows will be covered with an open ended tube for protection.
>>>> Just got to make a strap for those.
>>>>
>>>> Any comments?
>>>> Thanks
>>>> James
>>>>
>>>> [image: 20200704_142240.jpg]
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