Please teach the detailed steps for refilling oil while the hot oil is in operation

Oil top-up at room temperature: Before topping up the oil, the temperature of the heat transfer oil in the system should be reduced to below 70°C. Then, cold heat transfer oil should be poured in from the high-level tank; the vent valve at the highest point should be opened during this process to remove any air from the system. Add heat transfer oil until the level in the expansion tank reaches 25%, then proceed with oil boiling adjustments; dehydrate and remove light components from the heat transfer oil within the system, before raising the temperature to the operating level. Oil top-up during operation: When topping up oil in a heat transfer oil system while it is in operation, it must first be poured into the expansion tank, where it undergoes mixing, heating, expansion, evaporation, and degassing before entering the main circulation system via the expansion lines. This is done to prevent water or low-boiling-point substances present in the cold medium being added from entering the main circulation system directly.

I still don’t understand how to add heat transfer oil during operation! First: After adding the expansion tank, how can the system continue to operate while simultaneously circulating fluid for heating and dehydration? Second: The heat transfer oil is at a high temperature; when low-temperature heat transfer oil is added suddenly, doesn’t it expand rapidly?