The control valve is one of the terminal control elements of the automatic control system. Due to the existence of many high temperature and high pressure working conditions in the chemical plant, some media have strong corrosiveness and toxicity, and are flammable and explosive. When the valve packing leaks, it will not only cause waste of raw materials, but also cause serious pollution to the environment, even cause fire, explosion, poisoning and other life-threatening safety. Accident. The valve part of the control valve consists of the internal parts of the valve and the valve body. The internal parts of the valve include the valve core, the valve rod, the stuffing box and the upper valve cover, among which the stuffing box parts are used to seal the valve rod.


How to deal with the old leakage of control valve packing?


1, introduction


The control valve is one of the terminal control elements of the automatic control system. Due to the existence of many high temperature and high pressure working conditions in the chemical plant, some media have strong corrosiveness and toxicity, and are flammable and explosive. When the packing of valve leaks, it will not only cause waste of raw materials, but also cause serious pollution to the environment, even cause fire, explosion, poisoning and other life-threatening factors. Safety accidents. Therefore, enough attention should be paid to the leakage of the control valve packing. It is very important to select the packing reasonably in the design and selection. According to the packing seal of control valve, combined with many years' work experience and relevant data, through the analysis of the packing box structure of control valve, this paper introduces the characteristics and application occasions of polytetrafluoroethylene and flexible graphite packing, and briefly introduces the reasonable selection of packing for control valve.


2. Function and classification of control valve packing


Control valve: the valve part consists of the valve internals and the valve body. The valve internals include the valve core, stem, stuffing box and upper bonnet. The stuffing box component is used to seal the valve stem. It is an integral part of the valve body to prevent the process medium from leaking on the surface of the valve stem through reciprocating or rotary movement by elastic method. Almost all the valve stem seals are made use of. Stuffing box.


The packing of control valve is the packing material of dynamic seal, which is usually installed in the packing box of upper valve cover. Its function is to prevent the leakage of controlled medium caused by the movement of valve stem. Chinese style


The commonly used packing materials are mainly divided into two categories: polytetrafluoroethylene and flexible graphite. Chinese style


Two point one


Polytetrafluoroethylene (PTFE)


Polytetrafluoroethylene (PTFE) is a polymer compound formed by polymerization of tetrafluoroethylene. It has excellent chemical stability, corrosion resistance, sealing, high lubrication, non sticky, electrical insulation and good aging resistance. Its corrosion resistance is even better than that of glass and ceramics, even for strong acid, strong alkali and strong oxidant. It is an ideal sealing material. However, its temperature resistance is poor, and the polytetrafluoroethylene begins to crack at a very small amount above 200 ° under pressure, heating and creep, which affects the sealing performance, and it is not suitable for molten alkali or fluoride occasions. The commonly used PTFE fillers are:


(1) polytetrafluoroethylene forming and weaving packing: it is made of polytetrafluoroethylene bulk weaving and pressing. It is an opening material with good flexibility, durability, good sealing effect and convenient replacement. It is the most widely used material. Chinese style


(2) V-type polytetrafluoroethylene packing: generally, it is made of polytetrafluoroethylene bar by turning. The packing structure is V-type. Under the condition of compression at both ends, due to the small friction coefficient of polytetrafluoroethylene, it has the advantages of lubrication and good sealing performance. The characteristics of V-type packing ring are as follows: under the pressure of the medium in the valve, the lip of the packing outer ring is always close to the inner wall of the packing box when it is opened, so as to achieve static sealing. Under the same pressure, when the lip of the inner ring of the packing is opened, it is always close to the valve rod to ensure dynamic sealing, so that even if the valve rod moves up and down, it can also ensure the sealing performance. Chinese style


(3) tetrafluoro graphite packing: by adding part of glass fiber, graphite and molybdenum disulfide, the creep resistance and thermal conductivity of polytetrafluoroethylene can be improved, but the hardness increases, the corrosion resistance decreases, and the sealing performance decreases. Chinese style