Answer:
An expansion tank that is installed above the highest terminal unit is commonly known as a diaphragm-type expansion tank. This type of expansion tank is designed to accommodate the expansion and contraction of the water within a closed-loop heating or cooling system, which can occur due to temperature changes. By installing the expansion tank above the highest terminal unit, it ensures that any potential air bubbles will naturally rise to the expansion tank instead of getting caught in the pipes or terminal units. This maintains the efficiency of the system and helps to prevent system damage caused by high pressures.