What type of valve is used to control water flow and prevent backpressure?

The correct answer is a check valve, which is specifically designed to allow fluid to flow in only one direction, preventing backflow or backpressure in the system. This is crucial in plumbing systems to maintain proper water flow and protect against contamination. For example, if water were to reverse direction and flow back into a clean water supply, it could introduce contaminants that pose health risks.

Check valves function by using a disc, ball, or another moving part that blocks the flow of water when it attempts to reverse. This ensures that the water moves in the correct direction, thereby protecting the integrity of the entire plumbing system.

In contrast, while a ball valve is excellent for on/off control of water flow and offers minimal resistance to flow when fully opened, it does not inherently prevent backflow unless specifically designed as a non-return valve. A gate valve allows for full-flow applications but is not intended for flow control associated with backpressure. A pressure relief valve is primarily used to relieve excess pressure in a system to prevent bursting, rather than controlling water flow direction.