Installation Method for Lift-Type Check Valves

　　The function of a check valve is to allow the media to flow in only one direction, while preventing reverse flow. Typically, these valves operate automatically: when fluid flows in the forward direction, the pressure pushes the valve disc open; however, if the fluid tries to flow backward, the combined force of the fluid pressure and the disc’s own weight closes the disc against the valve seat, effectively stopping the flow. Among the types of check valves, the internal-threaded check valve and the butterfly check valve fall into this category. Specifically, they include two subtypes: the swing check valve and the lift check valve. The swing check valve features a hinged mechanism and a door-like disc that rests freely on an angled valve seat surface. To ensure the disc consistently lands precisely on the valve seat each time, the disc is designed with ample clearance around its hinge point, allowing it full rotational freedom while maintaining complete, even contact with the seat. The disc itself can be made entirely of metal, or it may incorporate a layer of leather, rubber, or even a synthetic coating—depending on the specific performance requirements of the application. When fully open, the swing check valve offers minimal resistance to fluid flow, resulting in a relatively low pressure drop across the valve. In contrast, the lift check valve has a disc that sits directly on the sealing surface of the valve body’s seat. Like the swing check valve, this type allows the disc to move freely up and down. However, beyond this key difference, the lift check valve operates similarly to a globe valve: fluid pressure lifts the disc off the sealing surface, while backflow causes the disc to descend and seal tightly against the seat, halting the flow. Depending on the operating conditions, the disc can either be constructed entirely of metal or feature a rubber gasket or rubber ring embedded within a metallic frame. As with globe valves, the flow path through a lift check valve remains narrow, which means the pressure drop across the valve tends to be higher compared to a swing check valve. Additionally, the lift check valve imposes fewer restrictions on flow rate, making it more suitable for applications where unrestricted flow is critical.

　　Installation method:

　　1. The disc of the swing check valve is circular and rotates around a pivot located within the valve seat passage. Thanks to the streamlined design of the internal flow path, this type of valve offers lower flow resistance compared to lift-type check valves, making it ideal for low-velocity applications and large-diameter systems where flow conditions are relatively stable. However, it’s not suitable for pulsating flows, and its sealing performance is slightly inferior to that of lift-style check valves. Butterfly check valves come in three main designs: single-disc, double-disc, and multi-disc types, which are primarily categorized based on the valve port diameter. These designs are specifically engineered to minimize water hammer effects when the fluid flow stops or reverses.

　　2. Lift-type check valve: This type of check valve features a valve disc that slides vertically along the centerline of the valve body. The internal-threaded check valve can only be installed on horizontal pipelines, while high-pressure, small-diameter check valves often use a spherical disc design. The body shape of the butterfly-type check valve is identical to that of a globe valve (making it interchangeable with globe valves), which results in a relatively high fluid resistance coefficient. Structurally, it closely resembles a globe valve, with the valve body and disc being the same components. A guiding sleeve is machined into the upper part of the valve disc and the lower part of the valve bonnet, allowing the disc to move freely up and down within the bonnet’s guide sleeve. When the fluid flows in the forward direction, the disc is pushed open by the fluid pressure. Conversely, when the flow stops, the disc automatically drops due to gravity, seating firmly on the valve seat to prevent backflow. In contrast, the straight-through butterfly check valve has its inlet and outlet fluid paths oriented perpendicular to the valve seat passage, whereas the vertical lift-type check valve aligns its inlet and outlet paths parallel to the valve seat channel—resulting in lower flow resistance compared to the straight-through design.

　　3. Swing Check Valve: A check valve in which the disc rotates around a pin located within the valve seat. The disc-type check valve has a simple design and can only be installed on horizontal pipelines, offering excellent sealing performance.

　　4. Lift-type check valve: A valve where the disc slides along the centerline of the valve body. The pipeline-type check valve is a newly developed valve type characterized by its compact size, lightweight design, and excellent manufacturability—it represents one of the key directions for the future development of check valves. However, its fluid resistance coefficient is slightly higher compared to the swing-type check valve.

　　5. Compression-type check valve: This valve serves as a shut-off device for boiler feedwater and steam, combining the functions of a lift-check valve with those of a globe or angle valve.