How to ensure the sealing performance of butterfly valve castings

As a key fluid control device, butterfly valves are widely used in many industries such as water, petroleum, chemical and environmental protection. Their sealing performance is crucial to ensure the normal operation of the system and prevent leakage. The following will discuss the optimization of butterfly valve sealing performance from several aspects such as material selection, sealing design, assembly process, testing and verification, and maintenance and care.

Material selection
The sealing performance of butterfly valves is directly related to the characteristics of the selected materials. Different working environments and media require different sealing materials. Commonly used sealing materials include:
EPDM (ethylene propylene diene monomer rubber): This material has excellent heat resistance and corrosion resistance, suitable for media such as water and steam, and can maintain good sealing effect at higher temperatures.
PTFE (polytetrafluoroethylene): Known for its excellent high temperature and chemical corrosion resistance, it is suitable for a variety of chemical media. Although its cost is relatively high, it is still the preferred material in demanding applications.
NBR (nitrile rubber): This material is suitable for oils and fuels, but its tolerance in high temperature water environment is poor, so it needs to be carefully considered when selecting.
Reasonable selection of sealing materials can significantly improve the sealing performance of butterfly valves to ensure reliability and safety under specific working conditions.

Sealing design
The sealing design is the core link to ensure the sealing performance of butterfly valves. An excellent sealing design should comprehensively consider the following aspects:
The shape and structure of the sealing ring: The design of the sealing ring must ensure that it can fit tightly against the valve seat when the valve is closed to form an effective seal. Common sealing ring shapes include O-rings and V-rings, etc. The appropriate shape should be selected according to the specific application during design.
Processing accuracy of the sealing surface: The flatness and finish of the sealing surface directly affect the sealing effect. It is necessary to ensure that the processing accuracy meets the design requirements to avoid leakage caused by rough or uneven surfaces.
Sealing compression force: When the valve is closed, the sealing ring should be subjected to appropriate compression force to ensure the sealing effect. The compression amount of the sealing ring should be reasonably calculated during design to prevent sealing failure due to over-tightening or over-loosening.

Assembly process
The impact of the assembly process of the butterfly valve on the sealing performance cannot be ignored. Improper assembly may cause seal failure. Here are a few key points to note:
Cleanliness: Before assembly, all components must be thoroughly cleaned to remove surface oil, dust and other impurities to avoid affecting the sealing effect.
Correct installation of the seal ring: The seal ring should be evenly placed in the designed groove to avoid distortion or damage. Be careful during installation to ensure the integrity of the seal ring.
Alignment of the valve stem and the butterfly plate: The connection between the valve stem and the butterfly plate must be accurately aligned to ensure that the butterfly plate can rotate freely in the valve body to avoid poor sealing due to eccentricity.

Testing and verification
After the butterfly valve is assembled, the sealing performance must be tested to ensure its reliability in actual use. Common testing methods include:
Air tightness test: Apply a certain air pressure when the valve is closed to check for leakage. A qualified butterfly valve should not have gas leakage under the specified pressure.
Liquid tightness test: For liquid media, a corresponding liquid tightness test is required to observe whether the valve leaks by applying liquid pressure.
Pressure test: Perform a pressure test under the specified working pressure to ensure that the butterfly valve can withstand the pressure under normal working conditions and prevent sealing failure due to excessive pressure.