Standard Hydraulic Valves: Ideal for reliability and safety

Hydraulikventile für normgerechte Sicherheit
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All hydraulic components used in safety-related parts control units have to comply with the relevant safety requirements. For example, hydraulic valves should automatically reach the basic position during power failures. This basic position must ensure a secure hold, as well as sufficient coverage in the case of slide valves.

Special valves are not necessarily required for this purpose. Rexroth offers a wide range of different standard valve types which meet these requirements and which can be used in safety-related control units according to the requirements of ISO 13849-1. However, standard-compliant function alone is not enough: In order to configure and evaluate the safety of a control unit, engineers need to consider various key performance indicators, which Rexroth has established for each product line:

  • The Mean Time to dangerous Failure, MTTFd, describes the average probability of a dangerous failure of safety-related components of control units, usually expressed in years
  • For components, the valve’s reliability, which is dependent on the application-specific switching frequency; designers often use the B10d value instead of the MTTFd value. This value indicates the number of cycles at which, from a statistical perspective, 10 percent of the components have failed and can thereby cause danger.
  • From these values, the machinery manufacturer calculates the probability of a dangerous failure per hour, PFHd – the lower the value, the safer the control unit.

A high B10d value lowers the PFHd of a safety control or enables simple structures (single channel instead of dual channel at a required performance level c). For these requirements, Rexroth sets the operational standard worldwide: Rexroth Standard directional valves achieve a B10d value of 40 million switching cycles!

Advantages:

  • Wide spectrum of standard valves
  • Scalable in function and performance
  • MTTFddetermined for each product line
  • B10d value: available with up to 40 million switching cycles