[PSUBS-MAILIST] Thruster bladders

[Rick Patton via Personal_Submersibles]

Hi Hank.
Do you happen to have a good picture of your set up? Not clear what you are
saying. How long is your vacuum tube and I assume it comes out of the can
but not back in? I woldn't think a rubber hose could inflate enough to
allow the heated oil to expand it enough before pushing out the two factory
"0" rings?
Rick

On Wed, Sep 15, 2021 at 3:31 AM hank pronk via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi Rick.  I have oil filled at the moment because they jettison.  I use a
> length of vacuum hose from a car engine because it is soft.  I intended to
> install a car suspension air bag and connect all the motors to that.   I
> don’t worry much about an air bubble because it will just compress to
> nothing.
>
> Sent from my iPhone
>
> On Sep 15, 2021, at 7:18 AM, Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> 
> Hi Rick,
>
> You'll find people here who love oil compensation, and others who love
> air. They both work, so I guess it's just a matter of what has worked for
> each person.
>
> I used oil initially. The method was to put two 90 degree nipples in the
> motor can, and attach about a foot of plastic hose to them. To fill, you
> disconnect the top nipple and add oil through the hose until it comes out
> the top nipple. The hose wraps around the can and with that extra length is
> supposed to act as a bladder. I found it worked, but only until I started
> diving my K250 to 250 feet. Then, I was getting internal build-up of
> pressure in the motors. In the end, I figured what was going on was that
> the compression of the hose was insufficient for the thermal contraction
> between the surface, where I'd filled the motors, and the very cold ambient
> temperature at 250 feet. At depth, water was forcing its way past the shaft
> seals, and then the seals would keep the motors pressurized as I rose. My
> solution was to go to a larger bladder, namely this:
>
>
> https://www.google.com/search?q=squeeze+bottles&rlz=1C1CHBF_enUS807US807&sxsrf=AOaemvLRC6ixUOHC7wIDhQcAL78ShVP-Sw:1631711091091&source=univ&tbm=shop&tbo=u&sa=X&ved=2ahUKEwig_9a_hYHzAhUgF1kFHRK2AW0Q1TV6BQgBEKkC&biw=1536&bih=664#spd=4605806885737196691
>
> That said, the larger bladder was something I implemented just before
> selling that sub, so never got to dive it. It was also always a problem
> getting every last bubble out. I'd spend ages doing that, then come back
> the next day and find a bubble in the hose. I was never able to solve that
> issue, and I think the only way would have been to assemble the motor in a
> bucket of oil. The other problem was that if there was an issue, such as
> the over-pressurization one above, my sub created an oil slick. That is NOT
> good, and can attract the wrong sort of attention even if you were to
> use an oil that is harmless.
>
> Now I use air compensation. So far, so good. On my first dive with the
> mechanical arm, I noticed bubbles coming from a hose when I extended the
> arm. The bubbles would cease when I retracted the arm. Closer examination
> showed a nick in the hose, which got pinched closed when the arm was
> retracted. The beauty of air is that if there's a leak, you can see and
> trace it immediately. With oil, I'd have had a small slick but no idea
> where it was coming from. Also, it worked well in the sense that no water
> entered the arm. I have a shutoff valve, so that a leak won't drain the
> sub's air supply, or another way would be to supply the air comp with a
> small independent cylinder.
>
>
> Best,
> Alec
>
> On Wed, Sep 15, 2021 at 12:13 AM Rick Patton via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> I am re thinking what to use for my oil expansion bladder. Would love to
>> hear from everyone who chose to go with an oil filled thrusters on what
>> they used and how they liked it. I remember someone saying that they used a
>> squeeze ball gas tank primer which I like because it is small but I just
>> spoke with someone who didn’t use a bladder and had never had a problem.
>> Rick
>>
>> Sent from my iPhone
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