Device for sampling fluid under pressure for geological site development monitoring

1) A device for sampling at least one fluid under pressure, comprising a sample chamber defining an inner volume intended to receive said fluid, characterized in that said device comprises a lower piston arranged in the lower part of said chamber, an upper piston arranged in the upper part of said chamber, an intermediate piston arranged between said lower and upper pistons, means for closing and opening said chamber by moving said lower piston, and means for moving said intermediate piston allowing to define a substantially constant volume for said chamber upon closing of said chamber.