I don’t think the bag will be de-pressurized !
You actually need to cool the oil to the lowest working temp with the bag pressurized, fill to the minimum acceptable oil level. Then seal everything leaving the bag pressurized. As the oil heats up the oil level will rise and the pressure inside the bag will increase. Since it is a sealed system the headspace air pressure will also increase. The oil level will rise above the minimum acceptable limit.
Unless anyone else has thoughts??
Best regards
John
    	
    	

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On Wed, Aug 1, 2018 at 8:03 AM -0700, "Nutting, Phil" <[log in to unmask]> wrote:










To my learned colleagues,

We have a situation that some think will work and others (myself included) think it is all wrong.  Let me give the setting.

40 gallons of dielectric oil, assume 8 pounds per gallon that expands with heat.
A 4 foot high container used for high voltage, filled with the oil.
Highest voltage in the tank is at the top so no air is allowed at the top.
An air bag (diaphragm) is installed at the bottom of the tank... that is filled with the oil.
Once the tank has finished filling with oil the air bag is inflated to set a desired expansion space and the oil ports are sealed.
The air bag is now depressurized presumably creating a cavity that can expand and contract with the oil as it changes temperature.

Now remember that the bag is at the bottom of the tank under about 360 pounds of oil and is expected to breath as the oil volume changes with temperature.

I maintain that because the air bag is at the bottom under 360 bounds of oil the bag will never inflate during oil cooling.
Having the bag or a diaphragm at the top would work as there is no pressure caused by the weight of the oil.

Can someone clarify the physics of the assumed function of the air bag placed at the bottom of the tank?

Phil Nutting  |  HVP Senior Development Engineer   |  Excelitas Technologies Corp

Lab: +1 978.224.4332   |  Office: +1 978.224.4152
35 Congress St, Salem, MA  01970 USA
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www.excelitas.com


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