Which type of valve is primarily used to prevent backflow in a boiler system?

The check valve is primarily used to prevent backflow in a boiler system due to its design, which allows fluid to flow in only one direction. When the fluid flows in the intended direction, the valve opens, permitting the flow. If the fluid attempts to reverse direction, the valve closes automatically, thereby preventing any backflow that could potentially damage the system or create unsafe operating conditions.

In contrast, other types of valves listed serve different purposes. A ball valve provides reliable isolation and is ideal for on/off control but does not prevent backflow on its own as it is not designed to automatically close in the event of reversal of flow. A gate valve is mainly used for isolation and can be fully opened or closed but does not offer backflow prevention. The globe valve is more suited for regulating flow rather than serving as a backflow prevention device. Consequently, the check valve's specific function makes it the correct choice for preventing backflow in boiler applications.