Failure lists for hydraulic and pneumatic components

Status:

completed 08/1990

Aims:

Hydraulic and pneumatic controls with safety functions must satisfy predefined requirements concerning their behaviour in the case of a failure. This behaviour is evaluated in the framework of a failure analysis. The latter analysis is based on a failure convention specifying which failures can be expected to occur on hydraulic and pneumatic components. Such information has so far been lacking in almost all of the pertinent standards and safety provisions. A failure convention (list of failures), however, is an indispensable prerequisite for test bodies which need harmonised assessment criteria to produce comparable test results. This project, initiated and supported by the expert commitees Iron and Metal II and III, is aimed to draw up a detailed list of failures for the most important hydraulic and pneumatic components.

Activities/Methods:

Since little information on the issue is available from literature and from manufacturers, it was necessary to rely mainly on experiences gathered over the years in the context of product testing and laboratory examinations. Two lists were to be prepared: one for the most important hydraulic components and one for the most important pneumatic components. Prior to publication, the lists were to be discussed with some of the users, to make sure they would be easily understandable.

Results:

Valves and hoses, but also cylinders, filters, sensors and other components were included in the lists, distinguishing hydraulic from pneumatic units. For each component two groups of failures are indicated: those that must be expected and those that can be excluded a priori; remarks and explanations are also included. It is possible now to assess hydraulic and pneumatic controls on the basis of these failure lists; the latter are also discussed in the context of standardisation (CEN/TC114 Safety of machines and devices) on the initiative of German experts.

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