What is the function of a lift check valve?

The function of a lift check valve is to prevent backflow of fluids, particularly in applications involving feedwater. This type of valve is designed to allow fluid to flow in one direction while automatically closing to prevent flow in the opposite direction. When the fluid flows in the correct direction, it lifts the valve disc from its seat, allowing passage. If there is any attempt for a reverse flow, the disc will resume its seated position, effectively blocking the backflow.

This mechanism is crucial in systems where maintaining the direction of flow is necessary for safety and operational efficiency, such as in boiler systems where feedwater needs to be delivered to the boiler but should not return. Other options like allowing flow in both directions or regulating steam pressure do not align with the primary purpose of a lift check valve, which is strictly for preventing backflow. Furthermore, mixing water and steam is not relevant to the function of this valve, as its design does not facilitate the mixing of different phases but rather ensures fluid flows in a predetermined direction.