Application of Slow-closing Sub Valve in Check Valves

To effectively mitigate the water hammer effect and expand the application range of check valves, this article explores a novel design—adding a slow-closing sub valve to the check valve. As an indispensable component in pipeline systems, the primary function of check valves is to open when the medium flows in the forward direction and close when it flows in the reverse direction, thus preventing backflow, avoiding the reversal of pumps and driving motors, and preventing the discharge of media inside containers. Although traditional swing check valves and lift check valves perform well in many applications, they are prone to induce the water hammer phenomenon during the closing process, which may cause potential damage to the pipeline system. Therefore, the design of adding a slow-closing sub valve aims to enhance the performance and reliability of check valves to better meet various industrial demands.

Basic Functions and Types of Check Valves

The basic function of check valves is to ensure the unidirectional flow of media. Based on structural forms, check valves can be divided into the following two main types.

1. Swing Check Valve

The valve disc of the swing check valve rotates around the pin shaft of the valve body, commonly used for the flow control of liquids and gases. When the medium flows in the forward direction, the valve disc opens, allowing the medium to pass through; and when the flow is in the reverse direction, the valve disc closes quickly, preventing the medium from flowing back. Although the swing check valve performs well in many applications, the potential water hammer phenomenon during its closure remains a significant issue. The water hammer phenomenon not only affects the safety of the pipeline but may also cause damage to connected equipment, increasing maintenance costs.

2. Lift Check Valve

The lift check valve (foot valve) uses a vertical centerline motion of the valve disc. This type of valve is particularly suitable for maintaining the water column required after stopping the pump to prevent backflow. Although the lift check valve can effectively prevent backflow, it is also prone to generating the water hammer effect when closing quickly, affecting the stability and safety of the pipeline system.

Causes and Impacts of Water Hammer Effect

The water hammer effect refers to the pressure fluctuations caused by sudden changes in flow velocity when a fluid flows in a pipeline. When a valve closes quickly, the kinetic energy of the fluid is converted into potential energy, causing a sudden increase in pressure inside the pipeline. The impacts of the water hammer phenomenon include:

Pipeline rupture: The high pressure may exceed the bearing capacity of the pipeline in an instant, leading to leakage or rupture.

Equipment damage: The water hammer effect may cause impact on pumps, valves, and other equipment, affecting their normal operation and even causing faults.

System instability: Frequent water hammer phenomena can lead to unstable system performance, increasing maintenance and operating costs, and reducing the service life of equipment.

Design and Working Principle of Slow-closing Sub Valve

To address the water hammer effect, this paper proposes the design of adding a slow-closing sub valve to the check valve. The design aims to achieve a smoother valve closing process, effectively reducing the occurrence of the water hammer phenomenon.

1. Structural Design

The structural design of the slow-closing sub valve is crucial, and its installation position is usually below or on both sides of the main valve disc, connected by threads. The main components include:

Valve disc: When the medium flows normally, the medium pressure pushes the sub valve disc open, allowing the medium to flow smoothly.

Buffer cylinder: The upper part of the sub valve body is designed as a buffer cylinder, which can accommodate the incoming medium and slow down the change in flow velocity.

Small hole design: The valve cover has small holes that allow the medium to flow out gradually when the valve disc closes, alleviating the problem of a sudden increase in pressure inside the pipeline.

Sealing structure: O-ring rubber seals are used to ensure effective isolation between the sub valve and the main valve, preventing leakage.

2. Working Process

During normal flow: The medium pressure pushes the sub valve open, and the medium flows into the main valve outlet through the small holes, the main valve disc opens and depressurizes, thus maintaining the normal operation of the system.

During reverse flow: When the medium flows in reverse, the main valve disc closes quickly, and the sub valve allows the medium to flow slowly into the buffer cylinder under the influence of the small holes. Due to the design of the buffer cylinder, the sub valve piston can close slowly, effectively preventing the occurrence of the water hammer phenomenon. This structural design makes the closure of the main valve equivalent to the fast closing phase, while the slow closure of the sub valve effectively controls the pressure change.

Slow-closing Sub Valve in Lift Check Valves

The application of the slow-closing sub valve in lift check valves is equally important, and its design features include:

1. Structural Improvement

A slow-closing sub valve is added between the main valve disc and the valve body bracket, and a gasket ring is added between the valve body and the bottom mesh to increase the lifting height of the valve disc. This design not only enhances the sealing performance of the valve but also effectively reduces the impact of the water hammer phenomenon.

2. Operation Process

During forward flow: When the medium pressure pushes the valve disc open and enters the main valve body cavity, the buffer piston is also pushed upward. At this time, the opening of the valve disc and the rise of the buffer piston are coordinated, maintaining the stable flow of the system.

During reverse flow: Since the buffer cylinder is filled with medium when opened, the medium gradually discharges through the gap between the valve disc and the buffer piston, and the closing process of the main valve disc is thus buffered, effectively controlling the water hammer pressure rise. This design significantly improves the safety and reliability of the lift check valve.

Conclusion

By adding a slow-closing sub valve to traditional check valves, the performance of check valves in preventing water hammer pressure rise has been significantly improved. This new design not only achieves effective coordination between fast and slow closures but also effectively reduces the impact of the water hammer phenomenon on the pipeline system, ensuring the safety and stability of the system. With the continuous advancement of technology, the application of slow-closing sub valves will be more extensive, providing superior solutions for various fluid control systems.