The valve stem bears tension, pressure and torsion forces during the opening and closing of the valve, and is in direct contact with the medium. At the same time, there is relative frictional movement with the packing. Therefore, when selecting the valve stem material, it must be ensured that it is in the specified It has sufficient strength, good impact toughness, abrasion resistance and corrosion resistance at a temperature below the temperature.
There should be an anti-static mechanism at the junction of the valve stem and the ball and the contact between the valve stem and the valve body to prevent static electricity from accumulating on the ball. The safety design of the valve stem should prevent it from being "blowed out" under working pressure. The anti-blow-out flange on the valve stem should be treated with an annular ring to reduce the coefficient of friction.

Characteristics of traditional valve stem processing technology
1.Traditional valve stem thread uses spiral flying knife, and the thread accuracy is not accurate; while using traditional chipless thread rolling, it is easy to be deformed and twisted.
2. The precision of the grinder used for the polished rod part is not high and it takes a long time.
3. The inverted part adopts two clamps and turns to pull down and seal, the concentricity is poor, and the inverted seal is easy to leak.
4. The end part is indexed by the indexing plate of a milling machine, which is slow in processing, many processes and time-consuming.

The characteristics of the new valve stem manufacturing process
1.The thread of the new valve stem adopts self-made extrusion, which has high thread strength and accurate precision.
2. The concentricity of the threaded part and the polished rod part overcomes the long-standing problems of easy distortion and easy damage to the thread rolling die in the domestic thread rolling process.
3. The precision of the polished rod part reaches the mirror effect, the opening and closing are easy, and the sealing is good.
4. The inverted part is formed by CNC technology at one time, with high accuracy and good inverted sealing performance.
5.The T-slot at the end part adopts forging forming process, which has high efficiency and low cost.
6. The whole set of valve stem production technology has reached the international advanced level. Under the strong corrosive, volatile and toxic and harmful process conditions, once the valve stem seal is damaged, the highly corrosive, volatile, toxic and harmful process medium will leak from the control valve stem If it comes out, it will bring serious consequences to the surrounding environment and personal safety. The use of bellows valve stem seal is a way to solve the above problems. Bellows are generally made of stainless steel. This special bonnet structure protects the stuffing box of the control valve from contact with fluid. Once the bellows rupture, the stuffing box structure above the bellows will prevent the serious consequences of the failure of the bellows. In engineering practice, the selection of the bellows seal should fully consider that the pressure rating of the bellows seal will decrease with the increase in temperature, there should be no solid particles in the fluid, and the longest cycle life of the bellows material, etc. . In places where the stainless steel is not resistant to corrosion by certain process media, such as wet chlorine gas, the small amount of hydrochloric acid contained in the wet chlorine gas will quickly corrode the stainless steel bellows.