Determining The Fail-Safe Position; Adjusting The Volume Restriction Q - Samson 3730 Series Mounting And Operating Instructions

Operating the positioner

7.1 Determining the fail-safe position

Define the fail-safe position of the valve (0 %) taking the valve type and the actuator's direc-
tion of action into account. Position the AIR TO OPEN/AIR TO CLOSE slide switch according-
ly:
− AIR TO OPEN setting
Signal pressure opens the valve, e.g. for a fail-close valve
The AIR TO OPEN setting always applies to double-acting actuators.
− AIR TO CLOSE setting
Signal pressure closes the valve, e.g. for a fail-open valve
For checking purposes: after successfully completing initialization, the positioner display
must read 0 % when the valve is closed and 100 % when the valve is open. If this is not the
case, change the slide switch position and re-initialize the positioner.
Note
The switch position is prompted prior to an initialization. After an initialization has been
completed, changing the switch position does not have any effect on the operation of the po-
sitioner.

7.2 Adjusting the volume restriction Q

Fig. 37: Volume restriction Q
The volume restriction Q serves to adapt the air output capacity to the size of the actuator:
− Actuators with a transit time < 1 s, e.g. linear actuators with an effective area smaller
than 240 cm², require a restricted air flow rate (MIN).
− Actuators with a transit time ≥ 1 s do not require the air flow rate to be restricted (MAX).
The position of volume restriction Q also depends on how the signal pressure is routed at the
actuator in SAMSON actuators:
96
MAX BACK
MIN SIDE
Q
MIN BACK
MAX SIDE
Transit time
Signal
pressure
Connection at the side
Connection at the back
* Intermediate settings are not permitted.
<1 s ≥1 s
MIN SIDE MAX SIDE
MIN BACK MAX BACK
EB 8384-5 EN