Swing Check Valve: The valve disc of a swing check valve is disc-shaped and rotates around the axis of the valve seat passage. Because the internal passage is streamlined, the flow resistance is lower than that of a lift check valve. It is suitable for low flow rates and large-diameter applications with infrequent flow changes, but not for pulsating flow. Its sealing performance is inferior to that of a lift check valve. Swing check valves are available in single-disc, double-disc, and multi-disc types, mainly classified by valve diameter. The purpose is to reduce hydraulic impact when the medium stops flowing or flows back.
Lift Check Valve: A check valve where the valve disc slides along the vertical centerline of the valve body. Lift check valves can only be installed on horizontal pipelines. For high-pressure, small-diameter check valves, a ball valve disc can be used. The valve body shape of a lift check valve is the same as that of a gate valve (it is interchangeable with gate valves), therefore its fluid resistance coefficient is relatively large. Its structure is similar to that of a gate valve; the valve body and valve disc are the same. The upper part of the valve disc and the lower part of the valve cover are machined with guide sleeves. The valve disc guide sleeve can move freely up and down within the valve seat guide sleeve. When the medium flows in the forward direction, the valve disc opens due to the thrust of the medium. When the medium stops flowing, the valve disc falls onto the valve seat by its own weight, preventing backflow. In a straight-through lift check valve, the direction of the medium inlet and outlet channels is perpendicular to the direction of the valve seat channel; in a vertical lift check valve, the direction of the medium inlet and outlet channels is the same as the direction of the valve seat channel, and its flow resistance is lower than that of the straight-through type.
Disc check valve: A check valve in which the valve disc rotates around a pin inside the valve seat. Disc check valves have a simple structure, can only be installed on horizontal pipelines, and have poor sealing performance.
Pipeline check valve: A valve in which the valve disc slides along the centerline of the valve body. Pipeline check valves are a relatively new type of valve. They are small in size, lightweight, and easy to manufacture, representing one of the future directions of check valve development. However, their fluid resistance coefficient is slightly higher than that of a swing check valve.
Pressure-operated check valve: This type of valve is used for boiler feedwater and steam shut-off, combining the functions of a lift check valve and a gate or angle valve.
In addition, there are some check valves that are not suitable for installation at the pump outlet, such as foot valves, spring-loaded check valves, and Y-type check valves.
