What is the purpose of a back flow valve in plumbing systems?

The purpose of a backflow valve in plumbing systems is to prevent the reverse flow of water. This is crucial in maintaining water quality and safety within plumbing systems. Backflow can occur due to changes in pressure within the system, which can cause contaminated water from non-potable sources to flow back into the clean water supply. The backflow valve acts as a safeguard, allowing water to flow in only one direction and thereby ensuring that there is no contamination of the potable water supply.

By preventing the reverse flow, backflow valves contribute to the overall integrity of the plumbing system, supporting public health and compliance with plumbing codes and standards. The other options relate to different aspects of plumbing but do not directly address the specific function of a backflow valve, which is solely focused on controlling and preventing the unwanted reverse movement of water.