Common Cause Failure - Ccf; Diagnostic Coverage; Fault Modes; Misuse - Emerson AVENTICS SV01 Betriebsanleitung

The safety function of the 5/2 safety valve is to drive a double-acting cylinder or
other pneumatic actuator forward when the two valve elements are actuated si-
multaneously, and to drive the cylinder or other actuator back to its "safe" home
position when both valve elements are switched off. A fault in the system where
only one valve actuates when switching on or only one de-actuates when switch-
ing off causes the safety valve to supply air to port 2 of the valve and to simulta-
neously open port 4 to exhaust (port 5). This in turn causes the cylinder or an-
other actuator to return to its "safe" home position.
Monitoring of the two proximity sensors by the user's external safety monitoring
system makes it possible to detect these fault situations and to shut off and pre-
vent further electrical energization of the solenoids.
The control outputs of the safety system must be designed and constructed to
meet the category and/or performance level requirements of the safety system,
as determined by the risk assessment of the machine. Normally, the outputs to
the solenoids is a dual-channel output from a safety relay or safety PLC.
2.2.2 Common Cause Failure – CCF
The product has been engineered and manufactured according to the basic and
well-tried safety principles of ISO 1389-1 and -2.
Critical failure modes and causes:
• Incomplete reversal - caused by incomplete return of solenoid valve B.
• The pressure applied at port 4 not being dissipated - caused by incomplete re-
turn of solenoid valve A.
• Failure of the safety function - caused by simultaneous incomplete return of
both solenoid valves (A and B).
Common Cause Failures (CCF) are failures of different components, resulting
from a single event. CCF are not to be confused with cascading faults or common
mode faults. Common cause failures can cause loss of the safety function, espe-
cially in dual channel circuits where both channels could fail simultaneously due
to a single event. The following measures ensure that failures due to common
causes are avoided:
• Maintain compressed air quality, i.e., filtration, pressure regulation, lubrica-
tion.
• Avoid compressor oils that can cause valve seals to swell, soften, or otherwise
deteriorate.
• Operate within prescribed temperature limits.
• Install the valve such that the normal stroke travel of the valve elements are
perpendicular to the main direction of machine vibration and/or mechanical
shock.
• Observe the permissible values for vibration and shock stress.
• Avoid external magnetic fields.
• Do not plug the valve exhaust port.
• The silencer is included in the scope of delivery. Make sure that the silencer is
not clogged. Otherwise it must be replaced (see

2.2.3 Diagnostic coverage

A diagnostic coverage of 99 % is achievable through appropriate integration of
the safety valve into the safety control system. The monitoring system must
check for the proper change of state of each valve sensor (S1 and S2) with each
change of state of the safety control system outputs to the valve solenoids (sole-
noid A and B of the pilot valves). Detection of a fault by the safety control system
must trigger a shut-off of the safety controller's outputs to the valve solenoids
(solenoid A and B of the pilot valves). See
NOTICE: On 5/2 versions of safety valve SV01 and SV03, in the event of a fault
where the side A valve element is not actuated and the side B valve element
sticks within a very small, specific range of its stroke, there is a possibility of a
condition where pressure may not be present in port 2. This fault is detectable,
because one position sensor's output will be switched HIGH (on) and the other
sensor's output will be LOW (off).

2.2.4 Fault modes

Danger of personal injury due to uncontrolled movement during pressure
drop!
In the event of a sudden pressure drop, uncontrolled movement may occur
caused by the machine if a 5/2-way safety valve is installed to control the actu-
ator.
Take safety precautions on the machine side. For example, provide a non-
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return valve! See g Fig. 6.
AVENTICS™ SV01/SV03/SV05 | R412027221-BAL-001-AC | English
g 11. Spare parts).
g 7.1 Function test.
WARNING
Danger of injury due to unexpected start-up of the machine!
When the pressure returns, for example after a sudden pressure drop, the
safety valve must be prevented from switching on.
Take safety precautions on the machine side.
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In the normal state, either both solenoid valves are energized (both sensors give
no signal), or both solenoid valves are de-energized (both sensors give a signal).
States deviating from this indicate an error.
Errors indicating a deviation from the normal state:
• Solenoid A and solenoid B of the pilot valves are energized simultaneously:
– S1 ON, S2 OFF
– S1 OFF, S2 ON
– S1 OFF, S2 OFF
• Solenoid A and solenoid B of the pilot valves are de-energized simultaneously:
– S1 ON, S2 OFF
– S1 OFF, S2 ON
– S1 ON, S2 ON

2.2.5 Misuse

Danger of injury!
Misuse may result in injury or damage.
The product must be used exclusively as intended.
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Misuse includes:
• Use outdoors
• Bypassing the safety function or diagnostics
• Failing to utilize the onboard sensors to verify valve operation on every cycle –
energizing and de-energizing
• Allowing continued operation of the valve when one or both valve shifted sig-
nals (from position sensors) are not confirmed.
• Use in reverse operation (reversal of supply and exhaust air)
• Operation in Low Demand Mode per IEC 61508
• Operating at pressures below minimum operating pressure or above maxi-
mum operating pressure.

2.3 Personnel qualifications

The work described in this documentation requires basic mechanical, electrical
and pneumatic knowledge, as well as knowledge of the appropriate technical
terms. In order to ensure safe use, these activities may therefore only be carried
out by qualified technical personnel or a trained person under direction and su-
pervision of qualified personnel.
Qualified personnel are those who can recognize possible dangers and institute
the appropriate safety measures, due to their professional training, knowledge,
and experience, as well as their understanding of the relevant regulations per-
taining to the work to be done. Qualified personnel must observe the rules rele-
vant to the subject area.

2.4 General safety instructions

• Observe the regulations for accident prevention and environmental protec-
tion.
• Note safety instructions and regulations of the country in which the product is
used.
• Only use the safety valve in perfect working order.
• Persons who do any work on or with the safety valve must not consume any
alcohol, drugs, or pharmaceuticals that may affect their ability to respond.
• Use only accessories and spare parts approved by the manufacturer.
• Comply with the technical data and ambient conditions listed in the product
documentation.
• If unsuitable products are installed or used in safety-relevant applications, this
may result in uncontrolled system operating states that may lead to injuries or
equipment damages. Therefore, only use a product in safety-relevant applica-
tions if such use is specifically stated and permitted in the product documen-
tation.
WARNING
WARNING
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