The valve is a control component in the pipeline fluid delivery system. It is used to change the cross section of the pipeline and the flow direction of the medium. It has the functions of diversion, cut-off, regulation, throttling, checkback, shunt or overflow pressure relief. For fluid control valves, from the simplest cut-off valve to a very sophisticated automatic control system used in a variety of valves, the variety and specifications of the valve nominal diameter from the very small instrument valve up to the diameter of 10m Industrial piping valves. The valve can be used to control the flow of various types of fluids such as water, steam, oil, gas, mud, various corrosive media, liquid metal and radioactive fluid. The working pressure of the valve can vary from 0.0013MPa to 1000MPa, working temperature From -269 ℃ ultra-low temperature to 1430 ℃ high temperature. Valve control can be used a variety of transmission methods, such as manual, electric, hydraulic, pneumatic, worm, electromagnetic, electromagnetic - hydraulic, electro - hydraulic, gas - hydraulic, spur gear, bevel gear drive ; Can be pressure, temperature or other forms of sensing signal under the action of the predetermined requirements of action, or do not rely on the sensing signal for a simple open or close, the valve driven by * or automatic mechanism to make hoist for lifting, Slipping, swinging or swiveling, thereby changing the size of its flow path area to achieve its control function. 1. Strength performance The strength of the valve performance refers to the ability of the valve to withstand medium pressure. Valves are mechanical products subject to internal pressure and must therefore have sufficient strength and rigidity to ensure long term use without rupture or deformation. 2.Sealing performance The sealing performance of the valve refers to the ability of the sealing parts of the valve to prevent medium leakage. It is the most important technical performance index of the valve. There are three parts of the valve seal: opening and closing parts and valve seat seal between the two contacts; filler and the stem and packing box with the Department of the valve body and the valve cover connections. One of the leaks is called leakage before, which is commonly referred to as lax, it will affect the ability of the valve to cut off the medium. For cut-off valves, internal leakage is not allowed. After the two leaks called leakage, that is, the medium leaked from the valve to the valve. Leakage will result in material loss, pollute the environment, serious accidents will result. For flammable, toxic or radioactive media, leakage is even more not allowed, so the valve must have a * sealing performance. 3. Flow properties of the medium flow through the valve will result in pressure loss (both before and after the valve pressure difference), that is, the valve on the media flow has a certain resistance, the media to overcome the resistance of the valve will consume some energy. From the energy conservation considerations, the design and manufacture of valves, to minimize the resistance of the valve on the flow medium. 4. Action performance 1). Action sensitivity and * This refers to the valve for the media parameters change, respond to the corresponding degree of sensitivity. For the valve, such as throttle, pressure reducing valve, regulating valve and other parameters used to adjust the medium parameters and safety valves, traps and other valves with specific functions, the functional sensitivity and reliability is a very important technical performance indicators. 2). Opening and closing force and opening and closing torque Opening and closing force and opening and closing torque is the valve to open or close the force or torque must be applied. Close the valve, the need to make the opening and closing seat and the seat between the two sealing surface to form a certain seal than the pressure, but also to overcome the valve stem and packing between the stem and nut thread between the stem end of the bearing and Other friction parts of the friction, which must impose a certain closing force and closing torque, the valve opening and closing process, the required opening and closing force and opening and closing torque is changing, the maximum value is in the closure of the final instantaneous or open The initial instant. When designing and manufacturing valves, they should strive to reduce their closing force and closing torque.