The ability of a valve to continuously maintain and complete a given functional requirement over a period of work time so that a given parameter value is maintained within a specified range is referred to as trouble-free, and when such performance of the valve is compromised Will have a problem. Valve failure classification mainly based on the characteristics of the fault occurs, the extent of the impact of failure, the cause of the failure and mechanical products failure mode characteristics such as failure occurs when there are sudden failure and gradual failure of two forms. A sudden failure is characterized by a step change in one or several given operating parameters. Belong to this type of specific failure mode valve disc and seat bonding, circuit contact is damaged, the diaphragm is damaged, the valve can not be sealed, valve disc drive mechanism or the valve is wedged. Progressive faults are characterized by gradual changes in one or more of the given parameters. Specific failure mode media through the filler, the valve body and cover flange and pipe and valve body flange connection leaks, due to wear and tear, corrosion or scale formation in the closure of a leak, due to the erosion of the valve Wear changes the hydraulic characteristics of the regulator, abrasive fluid flow to the body, abrasive wear on the part, wear on the stem nut or stem thread, and more. Valve failure on the operation of the system there are differences, some serious, some slight. After a serious fault, the valve will stop running. Specific failure modes include housing parts such as bonnets, housings, wedges, etc., disc drive parts such as stems, stem nuts and gears, bellows and fasteners (body and bonnet connection Bolt) and so on destroyed. After a minor fault, the valve can continue to function according to the requirements, but the effect is reduced. For example, packing leaks and leaks at gasket connections can be eliminated by re-tightening the nuts, eliminating the need to remove the valve from the pipe, eliminating circuit contact problems without removing the electrical equipment, Signal system malfunctions that can be eliminated without the need to disassemble electrical equipment. According to the characteristics of the fault and the degree of influence classification is largely assumed, for repairable valves and irreparable valves, the same fault mode may belong to different fault categories, so for different valves, fault mode is not Uniformity.