3. Architecture, configuration and applications
3.1. Architecture (actuator sizing)
For actuator architecture (actuator sizing) including a fail safe unit, the maximum
torques, run torques and operating times are major factors be taken into consideration.
Incorrect actuator architecture can lead to device damage within the safety-
related system!
Possible consequences are for example:Valve damage, motor overheating, contactor
seizure, defective thyristors, heating up or damage to cables.
→
Imperatively heed the technical data of both actuator and fail safe unit for actu-
ator architecture.
→
Sufficient reserves have to be provided to ensure that the actuator paired with
the fail safe unit are capable of reliably opening or closing the valve even in the
event of an accident or undervoltage.
For the guaranteed (minimum) torque provided by the fail safe unit during fail safe
operation, refer to the technical data pertaining to the product.The maximum torque
acting upon the valve is twice the amount indicated in the data. Torque peaks
occurring during sudden braking, e.g. while approaching the end position of
comparatively rigid valves are, however, excluded.They may also occur when
demanding the ESD function and the valve is blocked at the same time (i.e. has
already reached the fail safe end position).The excessive torque rate of these torque
peaks depends among others on the weight and the rigidity of the valve and may
significantly exceed the mentioned factor of 3.
During ESD operation, the constant force spring of the fail safe unit will operate the
valve at nominal torque to the end position and maintain the position. This will also
apply if a reduced torque (range) was selected for standard operation with the electric
actuator.
To prevent valve damage during safety operation, we recommend, depending on
the stiffness, sizing the valve to at least 3 times the maximum actuator torque.
During initialisation, no torque may be applied in opposite fail safe direction. For this
reason, the fail safe unit is not suitable for applications with butterfly valves in which
pressure or torque is applied in opposite fail safe direction while in the safety position.
Like any switch, the end position switches have a certain hysteresis. Some valves
still require a certain torque once the end position has been reached (metallic sealing
valves).To make end position setting easier, leading of the end position signalling
with reference to the end stop was additionally provided.This causes the end position
switches to trip shortly before actually reaching the mechanical end stop and to signal
the end position.The same signalling behaviour occurs when leaving the end position,
once they have left the mechanical actuator end position.The angle from signalling
the end position to reaching the mechanical end stop amounts to approx. 2.5° – 4.5°.
The torque applied at the actuator side input of the FQM must not exceed the nominal
torque indicated in the technical data pertaining to the FQM.
For further environmental conditions such as vibration, temperature, ... which have
to be heeded when specifying the architecture, refer to the indications in both technical
data and operation instructions
For applications critical to safety, protection against unauthorised operation has to
be provided. Depending on the project-specific risk assessment, this may take the
form of a special screw, access control (e.g. fence) or other measures.
3.2. Configuration (setting)/version
Configuration (setting) of safety-related functions is defined in the factory during fail
safe unit assembly and validated during final inspection. Subsequent modification
of the configuration by the plant operator is not permissible. Exception: Setting of
the end stops (refer to operation instructions) and – within certain limits – setting of
the fail safe operating time (see below).
8
Architecture, configuration and applications with non safety-related actuators
To Next Page
Loading...
