1. Basic types and working principles of check valves
Check valves can be divided into several common types according to their structure and working principle:
1. Piston Check Valve
There is a valve disc in the lift check valve, which prevents reverse flow by lifting and lowering the fluid pressure. Its advantage is good sealing performance and is suitable for medium and high pressure and large flow occasions.
2. Ball Check Valve
The valve disc of the ball check valve is a sphere, which is pushed open by fluid pressure. When the flow is reversed, the ball is pressed by pressure to form a seal. It is suitable for occasions with large flow changes.
3. Wafer Check Valve
The valve disc of the butterfly check valve is shaped like a small butterfly plate. It is usually installed in the pipeline. The valve disc opens with the flow of fluid and closes automatically when the flow is reversed. It is suitable for small-diameter and low-pressure pipelines.
4. Swing Check Valve
The valve disc of the swing check valve is opened or closed by rotation. It is commonly found in large-diameter and low-pressure pipelines and is suitable for occasions with relatively stable flow.
5. Check valve and stop valve combination (Y-type check valve)
This combination check valve combines the functions of the stop valve and the check valve. While preventing reverse flow, it can also play a role in regulating flow and flow rate.
2. Key factors in purchasing check valves
When purchasing check valves, there are several key factors to consider:
1. Media type
Check valves are often used to prevent fluid backflow, so the type of media (such as water, oil, gas, steam, etc.) needs to be considered. Different types of fluids have different requirements for valve materials and sealing methods:
- Water: Ordinary cast iron or carbon steel check valves can meet the requirements.
- Oil and chemicals: Corrosion-resistant and high-temperature resistant materials such as stainless steel and alloy steel are required.
- Gas: High-pressure resistant and lightweight check valves are usually required.
- Steam: Check valve materials that work under high temperature and high pressure and are resistant to high temperature, such as alloy steel and stainless steel, are required.
2. Working pressure and temperature
The design pressure and temperature range of the check valve directly affect the selection of its materials and structures. Common working pressure levels include: PN10, PN16, PN25, PN40, etc. The specific selection should be determined according to the actual working conditions of the pipeline system.
3. Valve body material
The selection of valve body material should be based on the specific requirements of the working environment. Common check valve materials are:
- Cast iron: Suitable for low temperature and low pressure environments such as water and sewage.
- Carbon steel: Suitable for general liquid and gas pipelines, but not suitable for corrosive media.
- Stainless steel: Suitable for corrosive media and high temperature environments.
- Alloy steel: Suitable for high temperature and high pressure environments, with good corrosion resistance and high temperature resistance.
4. Sealing performance
The sealing performance of the check valve directly affects its effect in preventing reverse flow. According to needs, choose the appropriate sealing method:
- Soft seal: Use rubber, polytetrafluoroethylene (PTFE) and other materials, suitable for low pressure and normal temperature occasions.
- Hard seal: Use metal materials as the sealing surface, suitable for high temperature, high pressure, corrosive fluid environment.
5. Flow and caliber
The selection of the check valve should be determined according to the caliber and flow requirements of the pipeline. Generally speaking, the check valve is suitable for large flow and large diameter pipelines. When selecting, you need to ensure that the valve diameter matches the pipeline to avoid excessive flow causing valve damage or poor sealing.
6. Operation mode
The operation of the check valve is usually automatic, but manual control can also be selected according to the needs of different occasions. Manually controlled check valves are suitable for systems with precise flow requirements, while automatic check valves are suitable for applications where fluid unidirectional flow control is required.
7. Installation method
The installation methods of check valves are usually:
- Flange connection: Suitable for large-diameter, high-pressure pipelines, easy installation, and good sealing effect.
- Clamp connection: Suitable for small and medium-diameter pipelines, easy installation, and space saving.
- Threaded connection: Suitable for small-diameter pipelines, easy installation, and suitable for low-pressure occasions.
8. Reverse flow speed
When purchasing a check valve, you also need to consider the speed of the fluid's reverse flow. Too fast a flow rate will cause the check valve to fail to close in time, and may even cause valve damage. Therefore, when selecting, ensure that the flow rate and valve response speed match.
3. Common applications of check valves
Check valves are widely used in various occasions where media backflow needs to be prevented. Common applications include:
1. Water supply system: used in urban water supply pipelines, industrial water systems, etc. to prevent water flow from flowing backwards and protect pumps and pipeline equipment.
2. Petroleum and natural gas: used in oil and gas pipeline systems to prevent oil and gas flow from flowing backwards and ensure the safety of pipelines.
3. Chemical industry: used to prevent media backflow in chemical reaction devices and avoid leakage of harmful substances.
4. Steam pipeline: used in steam pipelines to prevent steam backflow and protect the safety of boiler systems.
5. Heating, ventilation and air conditioning (HVAC) system: used for water flow control in air conditioning and heating systems to prevent water backflow in pipeline systems.
4. Selection case of check valves
Suppose a petrochemical plant needs to purchase a check valve to prevent fluid backflow in the pipeline system, especially in the gas pipeline system, which requires high pressure resistance and corrosion resistance. When selecting a check valve, you can consider the following points:
- Material selection: Select stainless steel or alloy steel to ensure corrosion resistance and high temperature resistance.
- Sealing method: Select metal hard sealing method to adapt to high temperature and high pressure working environment.
- Type selection: Select swing or ball check valve with good sealing performance.
- Connection method: Select flange connection method to ensure the high pressure bearing capacity of the valve.
5. Conclusion
When purchasing a check valve, it is necessary to comprehensively consider multiple factors such as fluid medium, working pressure, temperature, sealing performance, valve body material, installation method, etc. Check valves can effectively prevent fluid backflow and protect the safe operation of equipment. By selecting the appropriate type, material and connection method, the stability and safety of the system can be ensured.