A check valve, also called a one-way valve, is a device that allows the flow of fluids to move only in one direction. The primary purpose of a check valve is to prevent backflow in the system. Check valves are cheap, effective, and easy solutions to a potential issue. Backflow can cause a problem if the flow is contaminated and, therefore, contaminates the media upstream. There are various sizes, designs, and materials to ensure there is a check valve for every application. Two-way check valves are commonly used. Check valves with vents are used as three-way check valves to protect the incoming water supply from contamination caused by backflow. The atmospheric vent allows the disposal of purged water into an existing drain. An arrow on its bonnet indicates the check valve flow direction. Swing check valves are called ‘tilting-disc’ or ‘flapper’ check valves. They have a disc on a hinge (or trunnion) that swings open with an inlet pressure. The disc swings shut as the inlet pressure decreases or if there is backflow. If there is no spring to assist in closing, mounting orientation is important to consider to ensure that the disc swings shut with gravity. A dual disk or double door check valve has a central disk that is split into two semicircular doors that function independently hinged