Classification of valve failure is mainly based on the characteristics of the fault, the degree of fault, the cause of failure and mechanical products, such as the characteristics of failure mode, there are two forms of sudden failure and gradual failure. Sudden failure is characterized by a step change in one or more of the given operating parameters. The specific failure modes are of such a valve and valve seat bonding, circuit contacts and damage, membrane damage, the valve can not be sealed, the valve actuator or valve was wedged etc.. Progressive failure is characterized by a gradual change in one or more of the given parameters. The specific failure modes with medium cover flange and pipe connected with the valve flange leakage through the packing, the valve body and the valve, due to wear, corrosion or the formation of scale in the closed parts due to leakage, erosion wear of the valve flap valve hydraulic characteristics change, wear on the body of the abrasive fluid, abrasive the loss of parts of the stem or stem nut thread wear.
The effect of valve failure on the system operation is different, some serious, some slight. After a serious fault occurs, the valve will stop running. Specific failure modes have shell parts (such as the valve cover, casing, wedge, etc.) driving parts of the valve (such as stem, stem nut and the gear), bellows and fasteners (bolts connecting the valve body and the valve cover is damaged). Minor fault occurs, the valve can continue to use the functional requirements, but the effect is reduced. For example, by re tighten the nut can eliminate the faults of packing leakage and junction leakage gasket, no need to remove the valve from the pipeline failure can be eliminated, the circuit contact failure can be eliminated without removal of electrical equipment, timely detection and without the need for disassembly of electrical equipment can eliminate the signal system failure etc.. According to the degree of classification of fault characteristics and the influence is largely hypothetical, for non repairable type valve and valve repair in terms of class, the same failure mode of failure may belong to different categories, so for different valves, the failure mode is not unity
