[PSUBS-MAILIST] Thruster bladders

Fri Sep 17 16:18:11 EDT 2021

 Alec, yes, my hose is very soft allowing it to collapse easily.  So far it is working fine, but I am connecting to a suspension air bag this winter.  I may experience greater temperature swing now that I will be diving more often.  The hose system may not handle greater temperature changes, due to greater volume requirements.Hank
    On Friday, September 17, 2021, 06:37:55 AM MDT, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 My understanding is this...
In compensation systems, there's two things you are compensating for; the squeeze of air bubbles and the thermal contraction or expansion of the oil. Add those two together, and that's how much delta you need in the volume of the bladder. Hank, I'm not familiar with your setup, but I take it this hose acts as your (well, your sub's) bladder? I take it then it's a soft hose that can squeeze or stretch a bit.  All is fine if the bubble is small enough that the hose flexibility can handle it easily. If not, the downside of the bubble would be pressure on the thruster seals. But if you have no bubble, or a smaller one, there is less compressing for that hose to take care of. 
Best,Alec 
On Fri, Sep 17, 2021 at 5:33 AM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Rick, my rubber lines are currently flapping in the breeze sitting on top of my drop weight.  Just tie them up, with an arc in the hose, so the bubble is in the middle.  This way when the hose collapses it is in the middle, not at the end where it could be damaged by the edge of the plug.  Or taper the plug.   In my opinion, an air bubble is good in a hose.If you have a soft bladder, you can work to get rid of every bubble of air if you want because the bladder will expand and contract as needed.I see no point to worry about it, particularly with the bladder because the bubble will simple squeeze to nothing at the highest point of the bladder.I am trying to think of a reason why an air bubble outside the motor is a problem.  Maybe I am missing something.  If I were in salt water with expensive motors, i would try to have a small soft bladder.  I like the squeeze ball for individual locations, and an air bag for central location with multiple motors on it.I won't be travelling this fall other than local lakes.Hank
    On Thursday, September 16, 2021, 11:31:26 AM MDT, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Hankwould love a picture. Do you tie the 1' of vacuum hose to the housing so it's not flopping in the breeze? I thought I had heard conflicting ideas about, "make sure you get all the air out of the thruster and bladder" and others saying that they have a little air left in the bladder to allow for the hot oil expansion so I am confused. My thinking (which is limited) is that you can't have any air in anything because as you know, you can't compress a liquid so any air would compress and push out the factory "0" rings? Shoot me a picture if it's not too much trouble. Need to wrap my head around this better so I can pick a method and go for it. Are you going to the reunion?Rick
On Thu, Sep 16, 2021 at 2:27 AM hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Rick, the vacuum tube is about a foot long and comes out a threaded fitting in the housing.  You can drill and tap either end in most cases.  Choose the location well to make sure the fitting does not interfere with the bolts etc.  I have a youtube video on how to do this. I can email you a picture of the motor with the hose.  It is still a good idea to have a bladder, just be sure it is real soft.Hank
    On Wednesday, September 15, 2021, 03:17:00 PM MDT, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 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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