Valves can be classified into block valves, regulating valves,
check valves, diverter valves, safety valves and multi-purpose valves six categories based on their functions.
Block valves are mainly used for cutting off fluid passages, and check valves, gate valves,
plug valves, ball valves, butterfly valves, diaphragm valves and pinch valves also can be used for cutting off fluids.
Regulating valves are mainly used to regulate pressure and flow rates of the fluids, and regulating valves, throttle valves, pressure reducing valves and float regulating valves also have the regulating functions.
Check valves are used to prevent reverse flows of fluids.
Diverter valves are used to divert passages of the fluids or to separate the two-phase fluids, and slide valves, multiported valves, steam traps and air valves can also be used for separating the two-phase fluids.
Safety valves are mainly used for safety protection, which prevent boilers, pressure vessels or pipes from being damaged due to overpressure.
Multi-purpose valves are valves with more than one function. For example, stop check valves not only can cut off the fluids, but also can prevent reverse flows of the fluids.
Valves for industrial pipelines can be divided into vacuum valves, low pressure valves, medium pressure valves, high pressure valves and excess high pressure valves according to nominal pressure. Valves can be classified into normal temperature valves, medium temperature valves, high temperature valves and low temperature valves based on the working temperature. Valves can also be classified based on types of driving devices, connection types to pipes and valve bodies' used materials.
Valves can be named individually or in combination based on various classification methods, or they can be named according to the structural features of the discs or specific applications of valves. The basic parameters of the valve are working pressure, working temperature and diameters. For a large number of valves used in industrial pipelines, commonly used nominal pressure and nominal diameters are the basic parameters. Nominal pressure refers to the maximum working pressure which a valve with a certain material can stand at the specified temperature. Nominal diameters refer to the nominal inside diameter of the valve body and the pipe end.
Valves mainly have performance of strength, sealing, regulating, circulating, opening and closing according to their different types and applications. Besides considering basic parameters and performance of valves, performance of fluids such as corrosion, viscosity, toxicity and radioactivity should be taken into account when valves are designed and selected.
Generally, valves which are used for low pressure non-corrosive fluids are made of cast iron or cast copper; high and medium pressure valves are made of cast steel or forged steel; temperature or high pressure valves are made of alloy steel; valves which are used for corrosive fluids are made of stainless steel, plastic, anticorrosion alloy such as copper and nickel molybdenum alloy, titanium alloy and lead alloy or anti-corrosion cast iron and cast steel liners.
