Strange pipeline pump rotor

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One day, while working, I had to connect a pipeline pump’s coupling. The coupling consisted of two halves, with 4 semi-circular keys and 2 straight keys. To connect the coupling, it was necessary to lift the pump’s rotor slightly so that the semi-circular keys could fit into place; if the rotor wasn’t lifted, the screws couldn’t be tightened properly! The turntable didn’t get scratched either! Later, out of concern, they removed the rotor but still kept it in place! At first, I thought the keyway position was wrong! Later, upon inspection, it was found that the inlet valve was not closing properly, resulting in 4 kilograms of pressure inside the pump! The rotor descends automatically after pressure release! The medium pumped is gasoline! Once there is tension in the pump, the rotor rises and then stays in that position! I’m wondering how gasoline can lift the rotor