The Structural Characteristics of The Slow-closing Check Valve

As a valve that opens when the pipeline system flows forward and closes when it flows backward, the check valve is primarily used to prevent medium backflow, pump and motor reverse rotation, and medium discharge from containers. Currently, the most common types are the swing check valve, where the valve disc rotates around the valve body pin, and the lift check valve, where the valve disc moves along the vertical centerline of the valve body. However, both of these valve structures suffer from the phenomenon of rapid reduction in backflow speed to zero when closing, causing a sudden increase in pressure on the inlet side of the pipeline, resulting in destructive water hammer effects. Therefore, the production diameter of check valves is generally between 50 to 500 mm. To mitigate the water hammer effect and expand the application range of check valves, a solution involving the addition of a slow-closing auxiliary valve has been proposed. This design enhancement ensures smooth valve opening and closing while reducing water hammer pressure.



The slow-closing check valve is mainly used in water supply and drainage pipelines for clean water, raw water, sewage, seawater, and other media. It is installed at the outlet of water pumps to cut off media reflux, eliminate destructive water hammer, and safeguard the safe operation of pipelines and pumps. Its main features include:

1. Compact size, lightweight, with a structure length only about one-third of that of swing check valves.
2. Excellent performance of the slow-closing system, unaffected by the media in the pipeline. The valve closes rapidly and then gradually slows down, effectively preventing destructive water hammer.
3. Rubber soft sealing for good closure performance, wear resistance, and long service life.
4. Rubber cushioning ensures smooth opening and closing without vibration or noise.
5. Lower flow resistance compared to traditional check valves, leading to significant energy-saving effects.

Structural improvements have been made to swing check valves by adding a slow-closing auxiliary valve on the original valve disc. The auxiliary valve is installed below or on both sides of the main valve disc and connected by threads. During normal flow, the medium pressure opens the auxiliary valve, allowing the medium to flow into the main valve outlet through the small hole in the auxiliary valve, relieving pressure on the inlet side of the main valve, and balancing the pressure before and after the main valve. When the medium flows backward, the main valve disc quickly closes under the action of the reverse flow medium, while the upper part of the auxiliary valve serves as a buffer cylinder. As the auxiliary valve cover rotates into the upper part of the valve body with a small hole, a portion of the medium gradually flows into the upper chamber of the buffer cylinder through the small hole, and some of the medium flows back through the gap between the auxiliary valve disc and the piston rod, ensuring slow closing of the auxiliary valve. This structural design effectively prevents water hammer pressure increase by rapidly closing the main valve during the quick closing stage, followed by slow closing of the auxiliary valve, according to the hydraulic and mechanical transition mechanism of the pump station unit.

In summary, the improved check valves with slow-closing auxiliary valves offer stable opening and closing, compact structure, reliable performance, and reduced water hammer pressure. The simple design enhancements facilitate production, interchangeability, maintenance, and replacement of the auxiliary valve without affecting check valve operation.

For lift check valves, also known as bottom valves, structural improvements involve adding a slow-closing auxiliary valve between the main valve disc and the valve body bracket. A gasket is added between the valve body and the bottom net to compensate for the height of the valve disc lift. The buffer piston and buffer cylinder use rubber sealing, and the valve disc shaft is rigidly connected to the piston, with a small gap between the buffer cylinder and the valve disc shaft. When the medium flows forward, the pressure medium pushes the valve disc into the main valve body cavity, simultaneously pushing the buffer piston upward. When the medium flows backward, the buffer cylinder is already filled with medium when it opens, and due to the small gap between the buffer cylinder and the valve disc shaft, the medium gradually flows out through the gap, effectively controlling the water hammer pressure increase caused by pipeline water hammering.