Bidirectional Sealing Floating Ball Valves for High Temperature and Viscous Media (Part Two)

Process control
As the functionality of the valve becomes better, its structure becomes more complex. Therefore, higher processing technology is required to ensure the function. Now, each key part is analyzed separately.

(1) Valve seats
Under the premise of preventing high temperature plugging, the gap between the outer diameter of the valve seat obtained by reasonable material selection and accurate design calculation and the valve seat box of the valve body should be as small as possible to prevent materials from entering the gap and hindering the valve seat from effectively moving in the valve seat box. In addition to using the sharp scraper at the sealing surface of the valve seat to remove impurities on the surface of the ball, the outer diameter of the valve seat should also be kept sharp chamfered, so that the valve seat can clean and scrape the accumulated materials in the valve seat box during axial movement. The back of the valve seat also has a large chamfer. During the opening and closing process, the flow characteristics of the medium are used to discharge ash and slag.
 
(2) Disc springs
The thrust generated by the disc spring is sufficient, which should be able to effectively remove the medium adhering to the surface of the ball, and sufficient stability should be maintained. Therefore, the disc spring should have sufficient thickness and compression. The surface of the disc spring is flat, preventing impurities from entering the disc spring, blocking the buffer space, and restricting the axial movement of the valve seat and the ball.
 
(3) Valve bodies and valve bonnets
Because the valve seat and the ball move in parallel in the inner cavity of the valve as a whole, high machining accuracy is required. The seat box is clamped with the valve body at one time to ensure its coaxiality. Clearance fit between the valve body and the valve bonnet should be small to ensure that the valve seat box of the valve body and the valve cover has a good coaxiality, so as to ensure the smooth movement of the valve seat ball in the valve cavity.
 
(4) Pins
In addition to reducing the contact area with the valve seat and preventing the accumulation of medium, the pin also has an important function of force limit stop. Therefore, the flatness of the pin plane is very important. All pins should be kept at the same height. Under the action of medium pressure, the ball and valve seat move as a whole, and they should fall flatly on the pin. Otherwise, the valve seat will deflect and it will be skewed under the pressure, being jamming inside and not being able to rebound. In order to prevent the pin from expanding and loosening at high temperatures, spot welding can be performed on the joint of the pin and the support ring. In order to ensure the same height, the combined support ring and pin can be fine finished twice to ensure the same height.

(5) Graphite rings
In principle, graphite rings are required to be dense and have a certain degree of elasticity. It can effectively and reliably seal the valve seat and valve body under small thrust of the disc spring. And in a long period of time, the axial direction will not be shortened due to the compression of the force, which will cause the effective compression amount of the disc spring to become smaller, and the thrust drop will cause the ball to slide downward and affect the valve sealing.
 
(6) Support rings
The support ring is provided with a large-arc transition process blade. During the valve opening and closing movement and the medium pressure, the ball and valve seat move left and right, using the structural characteristics and medium flow to loosen and remove the accumulated materials to achieve the purpose of self-cleaning. In order to prevent the support ring from moving and entering solid materials, an interference fit or spot welding with the valve body should be adopted. At the same time, the maintainability of disassembly and assembly should be considered.
 
Conclusion
In practice, it is found that different structures should be used in different sections. There is no one structure suitable for all working conditions, and there is no one valve suitable for all positions. Therefore, design and selection should be made for different working conditions and positions so as to ensure the continuous, reliable and stable operation of chemical plants with minimum economic investment.