[PSUBS-MAILIST] Thruster bladders

Wed Sep 15 09:31:12 EDT 2021

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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