[PSUBS-MAILIST] oil compensation

Sat Sep 16 10:47:09 EDT 2017

 Alan, You have a point with the air cylinder, the piston does take a tiny bit of effort to move especially when the shaft seal is still in place.  That is why I put a spring assist on it.  A rubber membrane is probably better than a piston.  But this is working, so I will continue with it, but I will move it above the motors and install an internal spring from a starter solenoid.  The external spring is kinda ugly and just loos wrong ;-)Hank
    On Saturday, September 16, 2017, 7:19:00 AM MDT, james cottrell via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Many of the work class ROVs with oil compensation use the type of brake chambers seen on big trucks for compensation. Some of them use glycol instead of oil because its less damaging to the environment in the event of a leak.
Greg

      From: Alan via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Saturday, September 16, 2017 6:02 AM
 Subject: Re: [PSUBS-MAILIST] oil compensation

Hank,just had another look at a free 150 page ex military document," Handbook of Fluid-Filled, Depth/Pressure-Compensating SystemsFor Deep Ocean Applications" ( had it printed & bound) couldn't see any reference to using a weight for over-pressure. The system I drew is pretty typical. The volume of their compensators seemed to start at 500ml & go up from there. An amount of leakage must be expected, or a reserve volume is maintained as a fail safe in case a leak starts.  I remember a remark from either Carsten or Emile that they went to one compensator per motor because they couldn't isolate the thruster that was leaking when using one compensator for all thrusters.In the publication I think I can remember piston type systems not being popular because of the low pressures involved & the chances of themsticking because of "crut" in the marine environment. However these subswere going to serious depths. Cheers Alan

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On 16/09/2017, at 9:07 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Alan,I don't think there is a need to worry about constant pressure through the diaphragm stroke.  You would fill the compensator with fluid to the maximum level.  The amount of travel would be equivalent to the amount of air trapped in the system plus any expansion due to temperature change. These two things would be so minimal that the amount of travel would be so small the pressure  from the spring would stay quite constant.  I can not see the entire drawing because I can not move it over for some reason ;-(  .  Very clever Idea though using a weight.  You could take an  air cylinder with a bit of extra length and put a lead weight around the shaft inside the cylinder above the piston, and you would be done.Hank
    On Friday, September 15, 2017, 10:27:25 PM MDT, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hank got me thinking about compensators again.I had made an initial design for a compensator, using a springto produce over-pressure. This design is pretty standard in operation,with lots of variations.One problem with the spring is that it might be producing 8 pounds offorce at the start, but as the oil level goes down & the spring extends,the over-pressure is reduced. Some of the springs I have seen arepretty large, possibly in an effort to keep the pressure range in a narrowerband. 4-5 psi seems a normal over-pressure.If I replaced the spring with a cylindrical 5lb weight, I would get the same4lb (weight in water) over-pressure throughout the range of the diaphragms travel. Can anyone see a problem with this? Any comments. The lead may bounce around a bitduring transport but I don't think this would be a problem. My initial design is attached!Alan

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, September 14, 2017 12:37 PM
 Subject: [PSUBS-MAILIST] oil compensation

Hi All,Thank you Greg, just sent them a request.
I have tested my air cylinder compensator for my thrusters both in the pressure test and a couple days ago to 100 feet.   The set up seems to work with no water intrusion into the motors.  I have the cylinder mounted below the motors witch causes a small air pocket in the hydraulic fitting on top of the motor.  I am not worried about the small amount of air except the potential of oil being forced up past the air pocket.  This makes me think the compensating cylinder should be above the motors.  Then I wonder why does the compensating cylinder need oil in it at all.  As long as the bore in the cylinder has enough volume so the piston is not bottomed out at max depth.  I also have a small spring pushing the cylinder rod to create a small internal pressure above ambient.  Is my logic flawed?  it would be very convenient to eliminate the oil in the cylinder and would make the compensator  faster to react to pressure change say in a fast ascent.  Hank_______________________________________________
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