What component helps to join different sections of piping in refrigeration systems?

The correct answer is related to the role of the ninety degree reducing elbow in refrigeration systems. This component is essential for connecting different sections of piping, especially when there's a change in pipe diameter or direction. By allowing pipes to turn corners and maintain flow without significant pressure loss, the ninety degree reducing elbow facilitates efficient refrigerant movement throughout the system.

In refrigeration, maintaining proper flow and minimizing restrictions is crucial for operational efficiency and system performance. The design of reducing elbows specifically supports this by joining pipes of different sizes, which accommodates various components' requirements and ensures that the system operates effectively.

The other components listed do not serve the same purpose. For instance, the expansion valve regulates refrigerant flow but is not involved in connecting pipes. The pump casing serves to house the pump and does not facilitate piping connections. The condenser coil is responsible for heat exchange but does not play a role in the physical joining of piping sections. Thus, the ninety degree reducing elbow is the appropriate choice for this specific function in refrigeration systems.