what is the valve

A valve is a device that controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or controls various passageways. The valve is a control means in the pipeline fluid delivery system, which is used to change the passage cross-section and the direction of medium flow, having a deflector, cutoff, throttled non-return, shunt, or overflow relief function. For fluid control valves, shut-off valve from the most simple to the highly complex automatic control system used in a variety of valves, many varieties and specifications, the valve nominal diameter to pass from tiny instrument valve diameter of 10m, industrial piping with valves. Work pressure valve can be used to control various types of fluid flowing water, steam, oil, gas, mud, and a variety of corrosive media, liquid metal and radioactive fluids, valves 0.0013MPa to 1000MPa ultra high pressure, working temperature ultra-low temperature from -269℃ to 1430℃ high temperature.
The valve is generated with the generation of the fluid piping. Human history of the valve nearly 4000 years. People in Ancient China from the suction brine salt in the salt well, there was a bamboo pipe used cork valve. 1800 BC, the ancient Egyptians in order to prevent the Nile flood and the construction of large-scale water conservancy, have already adopted a similar wooden cock to control the allocation of water. These are prototype valve. The large number of applications of industrial valves, began after the invention of the steam engine from Watt. The beginning of the twentieth century cast iron, cast steel, forged steel, stainless steel, chrome-molybdenum steel, brass, ductile iron and other material of the valve. Used in various industries, various mining.
The valve, it is primarily made up of body, hoist components and valve cover three parts. Valve seat in the valve body, stem drive the valve opening and closing parts (disc) to do the lifting movement, the clutch valves and valve seat, the valve opening and closing.
The opening and closing mechanism of the valve (also known as the valve disc, spool), the stem and the drive device (handwheel). Stem with trapezoidal threaded screw on the valve cover, handwheel and valve fixed in the upper and lower ends of the valve stem, turn the hand wheel, the valve stem can be raised or landing to lead toward or away from the valve seat to close and open the valves and valve seat close match, rely on the pressure of the valve stem, the valve is pressed on the seat when the valve is in the fully closed state, the valve is quite tight.
Industrial pipeline valves can be divided into nominal pressure vacuum valve and low pressure valves, medium pressure valves, high pressure valves, high pressure valve; valve valve working temperature can be divided into the normal temperature, medium temperature valve, high temperature valve, low temperature valve; valve can also beby type of drive means, and the pipe coupling, and the use of the valve body material, etc. to be classified. The valve according to various classification methods alone or in combination named hoist member structural features or specific uses can also be named.
The basic parameters of the valve working pressure, temperature and caliber. For large-scale use in various industrial pipeline valves, commonly used nominal pressure and nominal diameter as the basic parameters. The nominal pressure is refers to a material of the valve, at a predetermined temperature, which allows to withstand the maximum working pressure. Nominal diameter nominal inside diameter of the valve body with tubes connected end.
Have different requirements for the valve depending on its type and purpose, sealing, strength, regulation, flow, opening and closing, etc. properties. In the design and selection of valve, to consider the basic parameters and performance, but also consider the performance of the fluid, including the phase state of the fluid (gas, liquid containing solid particles), corrosive, viscosity, toxic, flammable and explosive precious rarity and radioactive.