Final answer:
FDNY connections are fitted with lower check valves to prevent backflow or reverse flow of water in firefighting situations.
Step-by-step explanation:
FDNY connections are required to be fitted with a lower check valve. This valve serves an important function of preventing backflow or reverse flow of water. When the water is flowing through the connection, the lower check valve ensures that it only moves in one direction, preventing any possibility of water flowing backward.
This is crucial in firefighting situations where water is drawn from a source such as a hydrant or a fire engine and needs to be pumped into a building or a fire hose. Without the lower check valve, there is a risk of water flowing back into the source, potentially affecting the water supply or contaminating it with firefighting chemicals.
The lower check valve acts as a one-way gate, allowing water to flow forward but not backward. It operates based on the simple principle of buoyancy and pressure. When water pressure in the system is higher on one side of the valve, it overcomes the buoyancy force and opens the valve, allowing water to flow through. However, when the pressure decreases or is reversed, the buoyancy force pushes the valve shut, preventing any backflow.