[PSUBS-MAILIST] Thruster bladders

Sat Sep 18 17:08:00 EDT 2021

 Rick, it's going to be fantastic, and you've got a lot of water to explore. I have snorkeled off shore from Mauii (Molekino I think it was called) & some really great visibility. How far off diving do you think you are? Alan
    On Sunday, September 19, 2021, 08:47:23 AM GMT+12, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 HI AlanGood point about using a solvent to get the oil coating off but then having an explosion due to the brushes sparking. I also am in a situation different than most about the motors getting hot due to the ocean surface temperature but I don't see me running them for any length of time while on the surface as I will almost always have a mother ship that towes me from the ramp to wherever I need to go. I installed a digital temp gauge that measures the water so it will be interesting to see what the temp is at 350' as well as any noticeable thermal clines. My Brother in law worked at a place that sells nothing but gauges and controls so I got it at cost and figured what the hell? I did a shore dive with an old friend I used to work with offshore and it had been months since I had done that and I just kept thinking what it would be like if I were in my sub cruising the coral reefs with the fantastic viz and not worrying about an uptake in nitrogen and sipping on a Pepsi!Rick
On Sat, Sep 18, 2021 at 9:43 AM Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Rick, there are lots of pros & cons for running oilas apposed to air. I wouldn't put any solvent inside the housing in case it dissolves the coating on the winding wire, or something like that. And as a motor can also work as a generator, if you created a spark by turning the prop, perhaps you could blow the thruster to bits if the solvent gasses ignite! Some residue oil might be helpful lubricating. I am using silicone oil, as marvel mystery oilhas the potential to harm plastics inside the thruster. Oil compensating is better for cooling the motor, which may be advantageous travelling on the surface in warm Hawaiian waters. The motors coils in a brushed motor rotate in the centre & are not up against the housing for direct cooling through the can. Also oil compensation gives you a safety aspect (to a degree) if you get any sea water in. On the negative side, I've heard of thrusters dripping oil on land, with the expansion and contraction of the motors & the height of the compensating bladder. There is a small power loss. I have heard of people adjusting the brushes on their motors to avoid lifting of the brushes due to centrifugal force on the oil. (more of a problem on smaller motors) Carbon from the brushes can blacken the oil & so it needs to be changed. Air compensation is as you say, cleaner. You can see a leak. I spoke with the guys that sell the semi-dry Fugu sub, and they prefer air compensation saying that if they see an air leak they don't mind, as it is a sign the system is working. They were mainly operating in fresh water though! The minn kotas are designed to work on boats in surface water with no oil in them so no harm in doing that. Alan

    On Sunday, September 19, 2021, 06:12:45 AM GMT+12, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Thank's Hank and Allen for your explanations. This would maybe be a good topic for someone to go over in detail on a chalkboard at one of our conventions if there are others out there that are having the same problem wrapping their heads around this type of system?Here's another question for ya..... based on these recent discussions and the messes I have made on my shop floor, table and myself, I think I have decided to go with no oil at all and just go with air, but, I have already filled one thruster with the Marvel Mystery Oil and then drained it all out but everything inside still has a coating of the oil on it so should I put a small amount of a solvent inside the oil fill hole and slosh it around to try and get the small amount of oil that is left inside the housing out and if so, what would be safe to use without harming the coating that is on the copper windings or, is it OK to just leave what small amount of oil that is in there and run it now just on air? Rick

On Fri, Sep 17, 2021 at 2:01 PM Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Rick, Just a further explanation as to why you don't need all the air out of the thruster.... If the thruster was 1/4 full of air, and you had a large external bladder full of oil attached; if you descended to 300ft, the air in the motor would be compressed to 1/12 th its original volume and just be replaced by oil from the flexible bladder. The bladder, oil and air in the thruster & surrounding water will all be the same pressure. When people used to wrap a tube around the thruster and attach it to two nipples, there was very little volume in the tube to compensate for the air compressing, & so it was critical to get every bit of air out. Alan
    On Saturday, September 18, 2021, 05:45:19 AM GMT+12, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hank, I forgot your thrusters don't rotate like mine. I assume you are talking about the Id of the hose being damaged as it collapses if the bubble was at the end? I am still having a hard time wrapping my head around having any air in the system as I would think that when the external pressure increases as you descend, the extra pressure would be pushing on everything evenly and the only things that are weak enough to give are the bubble in a bladder or hose and the extra pressure trying to squeeze the bubble going past the two factory shaft O rings? Rick
On Thu, Sep 16, 2021 at 11:33 PM 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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