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22 DOC,F20,EDN Rev.: -
5.2 Failure Modes - Single Acting (Spring
return)
Spring return actuators may be “fail open” or “fail close”
depending on what happens when the air fails. This air failure
mode must be built into the actuator and maintained when the
actuator is built onto the valve.
In addition both these air failure modes may be either direct
acting or reverse acting depending on what happens at the
positioner when the 4 - 20 mA. signal fails or is reduced to it’s
lowest level.
5.0 Failure Modes / Ausfallarten / Storingen
4. Fail Open - Reverse acting
Input
signal
Rotary
actuator
Linear
actuator
F20
1
2
A
Close
A
3. Fail Close - Reverse actingInput
signal
Rotary
actuator
Linear
actuator
F20
1
2
A
Close
A
2. Fail Open - Direct acting
Input
signal
Rotary
actuator
Linear
actuator
F20
1
2
A
Close
A
1. Fail Close - Direct acting
Input
signal
Rotary
actuator
Linear
actuator
F20
1
2
A
Close
A
5.3
5.4
5.5
5.6
5.2.1 Changes for Reverse Acting
To change from the standard setup to reverse acting:
1. Change the tubing (see fig. 5.3 to 5.6).
2. Plug the unused actuator port.
2. Remove the cover.
3. Change the action jumper setting by setting both jumpers to
the right side (see fig. 5.2).
4. Replace the cover taking care that the “O” ring seal is in
place and the fixing screws are tightened correctly.
Action
1 2 Air Signal
Direct A Block Close Close
Direct Block A Open Close
Reverse A Block Open Open
Reverse Block A Close Open
Air connection
Failure