How do I proceed for taking samples?

At first, open the ball valve for the cooling water inlet and check if cooling water is flowing.
Carefully open the sampling valve and discharge only so much thermal oil in the disposal vessel until it is ensured that the thermal oil comes from the main flow and therefore it will be representative.

Only then fill the heat transfer medium in the sample vessel. After the extraction of the sample, the sampling valve must be closed tightly again. Now, also the cooling water inlet can be reclosed.