What does a swing check valve prevent?

A swing check valve is primarily designed to prevent backflow in a piping system, which is particularly important in applications involving pumps and sewage. When a pump is actively moving sewage from one location to another, the swing check valve ensures that the sewage does not flow back into the pump or the tank when the pump is turned off or if there is a drop in pressure. This is crucial for maintaining the integrity of the pumping system and preventing potential contamination or overflow issues.

By allowing flow in only one direction, the swing check valve effectively safeguards the system against the risks associated with backflow, such as sewage being pumped back to the source tank and creating sanitation problems. Thus, the role of the swing check valve directly relates to ensuring that one pump does not inadvertently pump sewage back to the tank when it should not, which aligns perfectly with the correct answer.