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Improvement of the ball valve seal

Author: Site Editor     Publish Time: 2019-03-28      Origin: Site


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The cast ball valve is an opening and closing device in the ash slag pipeline. The sealing on it directly affects the quality and service life of the industrial valves. In the past, an O-shaped rubber sealing structure was adopted, in which an O-ring was placed in an annular groove machined on a shaft, and then assembled into a hole formed in the sleeve part to form a seal of the shaft and the hole.


The sealing performance of the structure depends on the amount of interference in the design, that is, the amount of compression of the O-ring and the machining accuracy of the hole and the shaft part. The interference is too small, the sealing performance is poor, the interference is too large, and the O-ring is easily crushed during assembly, and the seal is ineffective.

 Improvement of the ball valve seal

The sealing structure is simple and easy to assemble. However, if the machining accuracy of the shaft and the hole is not high or it is difficult to improve the machining accuracy, in addition to the basic sealing performance is difficult to ensure or it is difficult to further improve the accuracy, the main disadvantage is the sealing material, which is still in the cylinder. It is difficult to ensure the sealing performance of the cast ball valve used in the wash water. The reason is that the switch of the ball valve is of a partial rotation type, and a 90° switch is often required. 

Due to the dynamic cooperation between the valve stem and the valve body, there is a certain gap. When the valve is switched, the medium exerts a huge thrust on the ball, which inevitably causes the valve stem to have a certain inclination. The force of the valve stem is biased to one side, and the side is seriously worn. And the ash water contains a large amount of suspended matter to erode the seal. The O-ring seal of the valve stem has a short life cycle, and the leakage phenomenon often occurs, which also has a certain influence on the site environment. Therefore, it is decided to improve the sealing structure and materials. The main starting point of the improvement is to assemble the shaft and the hole. In the middle, it is possible to adjust the amount of compression, and it is possible to ensure effective sealing without greatly improving the machining accuracy of the shaft and the hole.


Second, the industrial ball valve structure improvement and abrasive design

1, X-shaped seal ring structure


The X-shaped sealing ring has a sealing surface around it, and there are lubrication grooves on the outside of the sealing ring. This structure is superior to the O-shaped sealing ring, has low installation precision, good reliability, no maintenance, low price, and can also pass the gasket. The compression amount adjustment has been widely used in the sealing of various pressure grade cast valves, which can effectively prevent the occurrence of leakage, greatly prolong the service life of the valve and improve the reliability of the valve.


2, X-shaped seal material


The X-shaped sealing material is made of polyurethane (CPU) material, which can effectively solve the problems in the traditional O-ring. Castable polyurethane is a kind of sealing material that has passed the international comparison. It has large elastic modulus, good physical and mechanical properties, and can withstand large impact loads. Polyurethane has basically solved the problem of hydrolysis resistance, and the temperature resistance level is also constantly improved, greatly expanding the application of polyurethane. The use of cast polyurethane to produce X-shaped seals is simple in process and low in manufacturing cost. Its pressure resistance level can reach 60MPa or even higher, and the pressure holding effect is also quite good, basically reaching zero leakage.


3, the principle of the ball valve sealing


The working principle: When the bolt is tightened, the packing gland moves downward to press the adjusting pad, and the inner lip and the outer lip of the X-shaped sealing ring are simultaneously pressed against the sealing surface of the shaft and the hole through the extrusion of the V-shaped packing pad. To ensure reliable sealing, the main sealing performance depends on the pressing force of the tightening bolts during assembly and has little to do with the shaft and hole dimensional accuracy.


4, abrasive design

Ensure product use requirements and meet design requirements;

It is easy to demould and clear the mold, and it is easy to operate;

Low manufacturing costs;

The abrasive material is suitable for 45 steel;

The shrinkage rate is designed from 1.5% to 1.7%;

The 10° slope positioning has no flash, the precision of the product is guaranteed, and the yield is high;

The grinding tool consists of an upper die, a lining die, and an outer die.


5, the size of the filling cavity

The filling chamber determines the amount of seasoning according to the pressure of the ball valve and the size of the caliber. The width is determined by the size of the shaft. Pressure 0.6~2.5MPa, DN250mm or less to prevent an X-shaped seal ring; 2.5~10MPa, DN300 or more place two X-ring seals. The depth of the packing chamber is determined by the height of the timing pad, pressure transmission ring, and X-ring.


6, The pressure transmission ring

The pressure transmission ring is set at high pressure and large diameter. It is installed between two sets of X-shaped sealing rings. Its main function is to transmit the upper pressure and change the force state of the X-shaped sealing ring to force the X-shaped sealing ring. Radial deformation to achieve sealing performance.


7. Finite element analysis of X-shaped sealing ring

The X-ring is a lip seal that is used in combination with a pressure ring (filler gland) and a support ring (filler pad) to prevent media leakage.


8. Force analysis of X-shaped seal ring

The force of the X-shaped seal ring is transmitted to the X-shaped seal ring by the pressure of the pressure ring (filler gland). The bottom of the seal ring is supported by the support ring (filler pad) at three points, and the sealing surface of the shaft and the valve hole Evenly stressed, you can get a better sealing effect.


Third, the summary of the ball valve seal


Through improvement, the valve structure is more reasonable, the sealing is more reliable, the raw materials are saved, the cost is reduced, the service life is improved, the modification is fast, the investment is small, and the user's needs are met.

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