[PSUBS-MAILIST] oil compensation

Sat Sep 16 10:53:16 EDT 2017

I would be wary of any compensation mechanism which is orientation dependent.  If you were to become disabled due to a flooded tank or other situation that left you at an other than level attitude in the water, it may not function as intended, and you never want an emergency situation exascerbated by another equipment failure.

I think compensation bias is most often created by springs, but if you use compensators with a sealed back side, you could also use a regulated air source which would provide constant non-variable bias, and also could be centrally sourced to all individual compensators.

Sean

On September 16, 2017 3:59:52 AM MDT, Alan via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Hank,
>just had another look at a free 150 page ex military document,
>" Handbook of Fluid-Filled, Depth/Pressure-Compensating Systems
>For 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 them
>sticking because of "crut" in the marine environment. However these
>subs
>were going to serious depths. 
>Cheers Alan
>
>
>
>Sent from my iPad
>
>> 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 spring
>> to 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 of
>> force 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 are
>> pretty large, possibly in an effort to keep the pressure range in a
>narrower
>> band. 4-5 psi seems a normal over-pressure.
>> If I replaced the spring with a cylindrical 5lb weight, I would get
>the same
>> 4lb (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 bit
>> during 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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>> 
>> <compensator.jpg>
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>> <compensator.jpg>
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>
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