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Has anybody ever come across any pressure vessels (spacecraft or otherwise) that use more than one bladder; that is, to contain more than two fluids? Tanks with two fluids -- a pressurant and a propellant -- separated by a single bladder or diaphragm are common, but what about more?

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  • $\begingroup$ +1 for a creative idea. Would you care to expand on your inspiration to help us along a little? Were you thinking propulsion, heat pipes or batteries/fuel cells? $\endgroup$
    – Puffin
    Mar 14, 2017 at 23:29

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The only thing I've ever heard of like that is from the petrochemical industry (you did say "otherwise"...)

enter image description here

It's a pressure vessel containing natural gas, oil, and water. Used at the outlet of wells to separate what comes out of the well.

Doesn't really have a bladder though.

It's called a "three-phase separator" although that is quite a misnomer IMHO.

Image source

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Normally the propellants are stored separately, especially hypergolics, which spontaneously combust upon contact with one another. However SpaceX currently uses Composite Overwrapped Pressure Vessels (COPV's) filled with liquid helium inside of the liquid oxygen tank. The helium is heated and then released to pressurize the tank. So, technically the helium is stored inside the liquid oxygen tank. Also the S-IVB and I believe the S-II stage of the Saturn V rocket had common bulkheads. This means that the liquid hydrogen and liquid oxygen are just about stored in the same tank, except thy are separated by 2 thin sheets of aluminum and resin. This is all I could think of for 2 propellants/pressurants stored in almost the same tank.

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  • $\begingroup$ The temperature of liquid hydrogen and oxygen is very different, LH2 is much colder as LOX. At the temperature of LH2 oxygen is solid. If LH2 and LOX are separated by a common bulkhead without sufficient isolation, solid oxygen may exist on one side of the wall and heavily boiling LH2 on the other side. A lot of propellants could be lost in this way. $\endgroup$
    – Uwe
    Mar 14, 2017 at 20:05
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    $\begingroup$ Yes this is true, I just said they were about stored in the same tank, except they are insulated and separated by aluminum and resin.history.msfc.nasa.gov/saturn_apollo/documents/Third_Stage.pdf $\endgroup$ Mar 14, 2017 at 20:09
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Safety concerns aside, it would be difficult to ensure that the delivered mix ratio remains correct and constant. Also, if cryogenic fuels are used their temperatures are usually incompatible.

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