What type of valve is used to relieve pressure in hose lines after the discharge gates are closed?

The valve used to relieve pressure in hose lines after the discharge gates are closed is a drain valve. This type of valve is specifically designed to allow excess water and pressure to escape, which is essential after operation to prevent potential damage to the hose or fittings.

When the discharge gates are closed, the pressure that remains can create a hazardous situation if not properly managed. By opening the drain valve, firefighters can safely release the pressure and any residual water from the hose lines, ensuring that the hoses remain in good condition for future use and preventing leaks or ruptures.

In contrast, a relief valve is typically used in systems to release pressure above a set threshold, but it is not the primary means of managing hose line pressure after the discharge gates are closed. Rather, its main function is to prevent overpressure situations in fixed installations. Control valves manage the flow of water in the system and are not specifically designed for pressure relief, while shut-off valves are meant to completely stop the flow of water rather than relieve pressure.