VOFA-L26-T32C-M-G14-1C1-...
Festo – VOFA-L26-T32C-M-G14-1C1-... – 1409NH English
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2.2
Failures due to common cause (common cause failure – CCF)
Common cause failures cause the loss of the safety function, as both channels in a two-channel system
fail simultaneously in these cases.
Through the following measures, you ensure that common cause failures are avoided:
–
Comply with the compressed air quality to avoid flash rust particles in particular (for example
caused by servicing work), and also comply with the residual oil content (maximum 0.1 mg/m³
when using an ester-based oil, which is contained, for example, in compressor oil).
–
Comply with the operating and control pressure limits, if necessary, through the use of a pressure-
relief valve.
–
Comply with the temperature range.
–
Comply with the permissible values for vibration and shock stress, and preferably arrange the valve
longitudinal axes vertically to the main direction of vibration.
–
Comply with the maximum permissible test pulse length when used at timed safety outputs.
–
Comply with the maximum permissible strength of external magnetic fields.
–
Avoid clogging of the silencer and blocking of the port (3) (
chap. 6.2).
Note
Loss of the safety function
Non-compliance with the technical data can lead to loss of the safety function.
•
Observe the technical data
chap. 13.
2.3
Diagnostic coverage (DC)
A DC of 99 % can be achieved through an appropriate integration of the control block in the control
chain and corresponding test equipment. The change of the corresponding sensor signal in the machine
control system must be queried here each time a valve is actuated. If a fault is detected by the test
equipment (e.g. missing sensor signal), appropriate measures must be taken to maintain the safety
level (
chap. 8).
Of particular note here are the following failure modes:
–
Failure of one of the two solenoid valves (V1 or V2) to switch back completely. This fault can result in
a reduction of the exhaust flow rate (
chap. 13, Tab. 9).
–
Failure of the two solenoid valves (V1 and V2) to switch back completely at the same time. This fault
can result in a failure of the safety function.
