The valve is a pipe accessory used to open and close the pipeline, control the flow direction, adjust and control the parameters (temperature, pressure and flow) of the transport medium. According to its function, it can be divided into shut-off valve, check valve, regulating valve and so on.
The valve is the control component in the fluid transportation system, and has the functions of cut-off, adjustment, diversion, prevention of reverse flow, voltage stabilization, shunting or overflow pressure relief. Valves used in fluid control systems range from the simplest globe valves to various valves used in extremely complex automatic control systems.
The valve can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metals and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves (201, 304, 316, etc.), chromium-molybdenum steel valves, chromium-molybdenum-vanadium steel valves, dual-phase steel valves, plastic valves, non-standard customized valves, etc.
The sealing performance of the valve refers to the ability of each sealing part of the valve to prevent media leakage, and it is the most important technical performance index of the valve. There are three sealing parts of the valve: the contact between the opening and closing parts and the two sealing surfaces of the valve seat; the cooperation between the packing and the valve stem and stuffing box; the connection between the valve body and the bonnet. The leak in the previous one is called internal leakage, which is usually called the tightness, which will affect the ability of the valve to cut off the medium. For cut-off valves, internal leakage is not allowed. The leakage in the last two places is called external leakage, that is, the medium leaks from the valve to the outside of the valve. External leakage will cause material loss, pollute the environment, and even cause accidents in severe cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.
