Check valves, as crucial safety protection devices in industrial piping systems, their core function is to ensure one-way flow of media and effectively prevent backflow. This article will delve into their working principles, main types, selection key points, and common issues, providing you with comprehensive technical guidance.

 

A check valve is an automatic valve that opens and closes依靠 the pressure difference generated by the media's own flow. When the media flows in the designed direction, the fluid pressure pushes open the valve disc, and the valve opens to allow passage; when the media stops flowing or attempts to reverse, the valve disc automatically closes under the action of reverse pressure, self-weight, or spring force, thereby cutting off the flow path. Its main roles include preventing damage to equipment such as pumps and compressors due to media backflow, avoiding downstream media contamination of upstream systems, maintaining stable system pressure, and preventing siphon effects.

 

Based on structural forms, check valves can be divided into various types, each with its applicable scenarios:

1. Lift Check Valves: The valve disc moves vertically along the centerline of the valve body. They have good sealing performance and reliable operation but have large flow resistance and must be installed in horizontal pipelines. They are suitable for high-pressure, small-diameter occasions such as boiler feed water.

2. Swing Check Valves: The valve disc rotates around a pivot pin. They have small flow resistance and large diameter but are prone to water hammer and noise when closing. They are commonly used in water, steam, and oil pipelines.

3. Butterfly Check Valves: The valve disc is a disc structure that rotates around a central axis. They are small in size, light in weight, and compact in structure but have relatively poor sealing performance. They are suitable for large-diameter water treatment and HVAC systems.

4. Ball Check Valves: A ball is used as the valve disc, and opening and closing are achieved依靠 rolling. They have a simple structure and good sealing performance. They are suitable for small flow rates or media with particles but are not resistant to high pressure.

5. Axial Flow Check Valves: The valve disc moves along the pipeline axis, usually with spring assistance. They have minimal flow resistance, quick response, and low noise but high cost. They are mostly found in long-distance oil and gas pipelines.

6. Diaphragm Check Valves: Flexible diaphragms are used to control the flow direction. They have no internal leakage and are suitable for high-purity media such as in the medical and food industries, but their pressure and temperature resistance capabilities are limited.

 

Correct selection is the key to ensuring the effective operation of check valves, and the following factors need to be comprehensively considered:

- Media Characteristics: Including type (water, steam, gas, or corrosive media), cleanliness, and temperature to determine the valve body material (such as cast iron, stainless steel, or PVC) and internal structure.

- Working Condition Parameters: Covering working pressure rating (such as PN16, CL150), pipeline diameter (DN size), and connection method (flange, threaded, or wafer).

- Installation Requirements: It must be ensured that the valve installation direction is consistent with the media flow direction (the valve body is usually marked with an arrow), and attention should be paid to certain types (such as lift type) which are only for horizontal installation.

- Performance Requirements: If quick closing is needed to prevent water hammer, a silent type with a spring should be selected; if zero leakage is required, a high-sealing design is needed.

 

1. Water Hammer Phenomenon: Pressure shock caused by sudden changes in flow velocity can be alleviated by selecting quick-closing valves such as axial flow type.

2. Valve Disc Oscillation: Low flow velocity causes the valve disc to fail to open stably. It is necessary to verify whether the working condition flow velocity conforms to the valve design range.

3. Installation Errors: Reversing the direction will make the valve ineffective. Be sure to confirm the flow direction indication before installation.

4. Lack of Maintenance: Regularly check the wear of the sealing surface and the flexibility of moving parts to prevent jamming or leakage.

 

In conclusion, the selection and application of check valves need to be closely combined with actual working conditions. Understanding their principles and type differences and following selection specifications can ensure the safe and efficient operation of the piping system.