Pneumatic ball valves are widely used in the gasification field of coal chemical plants. Due to the special media such as solid particles, ash, and sulfur in the operating conditions, they should meet the requirements of wear resistance, corrosion resistance, erosion resistance, prevention of scaling and scarring, rapid opening and closing, and frequent actions. At the same time, they should have good sealing performance to achieve high efficiency, low energy consumption, and safe and reliable operation of the equipment.

Analysis of the Causes of leakage in Pneumatic Ball Valves

After the valve has been in use for a period of time, problems such as jamming and incomplete opening and closing occur. The main sealing surfaces of the valve, such as the ball and the valve seat, are severely eroded, and the sealing surfaces are damaged. In more severe cases, the ball and the parts inside the valve cavity are damaged, resulting in internal leakage of the valve. The increase in the gap between the valve stem and the stuffing box leads to external leakage of the valve. Tianjin fire butterfly valve‍

① Internal leakage of pneumatic ball valve:

Based on a comprehensive analysis of various gasification technology processes, media and flows, the ball valves at key parts are not only affected by the solid content in the medium, but also have a high frequency of valve opening and closing. They are influenced by the throttling structure of the valve's designed flow path. When the medium flows through the valve, its flow rate is amplified, and the pressure difference before and after the valve also increases, resulting in particularly severe erosion and wear on the valve. Some ball valves are partially melted by high-temperature media. Due to the effect of surface tension, a large number of fine spherical particles are formed, which will increase the erosion and wear of the valve and the sealing surface. Powder enters or accumulates dust in the valve seat spring cavity, causing the spring to fail or flip over, etc. The grinding accuracy of the ball valve and the valve seat does not meet the standards. The concentricity of the ball valve is poor, and the surface roughness is also poor, which is prone to internal leakage.

The valve ball is generally made of forged stainless steel with a surface coating of chromium carbide, with a thickness of only 0.3 to 0.5mm and a hardness of HRC58 to 72. Due to the grinding effect during frequent opening and closing, the sealing surface is scratched, and the valve seat and valve ball are severely worn. Over time, the wear-resistant layer is also prone to being worn off, which can easily cause serious internal leakage of the valve. Tianjin fire butterfly valve‍

② External leakage of pneumatic ball valve

The unreasonable design of the valve stem packing structure, the coaxiality of the valve ball and the valve stem exceeding the tolerance, and the unreasonable selection of the valve stem material and other factors have led to increased wear of the valve stem and packing during the opening and closing process of the valve, severe wear of the mating surface between the valve stem and packing, resulting in a reduction in the valve stem diameter and leakage of the medium in the valve flow passage along the axial direction of the valve stem.

2. Improvement measures for pneumatic ball valves

① Renovation of the internal sealing structure

The valve seat of the hard-sealed ball valve adopts a scraping structure design, which enables the ball and the valve seat to have a self-cleaning function during the opening and closing process. This effectively prevents the sedimentation and adhesion of particles between the ball and the valve seat, ensuring smooth and continuous valve operation without jamming. The secondary valve seat and the valve body, as well as the Spaces between the main and secondary valve seats, all adopt special structural designs. Metal rings are added between the sealing packing to enhance the rigidity and toughness of the packing, further effectively preventing impurities from entering the spring cavity behind the valve seat, ensuring the long-term effective operation of the spring. Meanwhile, the spring uses a cylindrical spring, which can achieve uniform force distribution on the valve seat, avoid uneven wear on the sealing surface, and extend the service life of the sealing surface. Tianjin fire butterfly valve‍

②. Renovation of the external sealing structure

Both the upper and lower end faces of the valve stem are positioned by bearings. The valve stem not only rotates relatively but also serves as a guide, ensuring the coaxiality requirement between the valve stem and the ball. The upper part of the packing adopts a disc spring, which guarantees the preload force for the packing's sealing performance. It is designed in a live load form, providing a good sealing effect and ensuring the service life of the sealing material.

③ Adopt new processes and new materials

Depending on different working conditions, the valve ball can be made of ceramic-metal composite balls or coated with materials such as tungsten carbide and zirconium carbide on the surface. The sealing surface of the valve seat adopts supersonic spray hardening technology, with a hardness of HRC≥64 and up to HRC72 or above. This valve can adapt to the vast majority of harsh working conditions and is resistant to erosion and wear. Tianjin fire butterfly valve‍

After the above improvements to its internal and external sealing structures, the wear resistance of the valve sealing surface and the packing seal performance have been enhanced, and the service life of the equipment has been prolonged. The sealing structure of the pneumatic ball valve is relatively reasonable and meets the working conditions.

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