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I wished they had mentioned something about prist in that link....
I'm getting the feeling that when people ask for prist, it is similar to when I ask for mayo on my sandwich at the deli.
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Prist is an anti-icing additive that lowers the freezing point of water.
Jet fuel contains small amounts of dissolved water. At altitude, the cold temperatures make it impossible for the water to remain in a dissolved state, so water can actually appear in the fuel as supercooled droplets. This is detrimental because it can freeze in lines and at filters.
Prist isn't very soluble in fuel, but it is in water. Therefore, when water particles form, the Prist is dissolved in it, lowering the freezing point to prevent it from freezing in lines/filters.