FIELD: sampling.SUBSTANCE: invention relates to a device for sampling media under pressure and the use of this device for sampling a controlled well. Device comprises a sampling chamber, inside which there are upper, lower and intermediate pistons, means for closing and opening the chamber by moving the lower piston and the means for moving the intermediate piston. Intermediate piston is either at a constant distance from the lower piston, or at a constant distance from the upper piston, thereby setting a constant chamber volume. Upper and lower pistons can be connected by a connecting rod through which the intermediate piston slides. Application of the device includes the steps of transferring the sampler to an open position, descending it into a controlled well, maintaining it for a predetermined time, transferring to the closed position, lifting the sampler to the surface, moving the medium from the sampling chamber and analyzing the sample.EFFECT: reliable sampling, no need to open the sampler in the well
