Samson 3755, Mounting And Operating Instructions, Page: 23 / 32

EB 8393 EN 23
Mounting and start-up
5.3.1 Adjusting the bypass
restriction
For a stable loop performance, the bypass
restriction must be adjusted to meet the con-
trol loop requirements:
1. Undo the lock nut (
Fig. 1 , 4.1) and use a
4 mm Allen key to turn the bypass
restriction screw (4) clockwise into the
restriction seat as far as it will go. Make
sure that the lock nut does not get
tightened.
2. From this adjusted position, turn the by-
pass restriction screw counterclockwise
by three full turns.
3. Hold the bypass restriction screw station-
ary and tighten the lock nut with a tight-
ening torque of 3 Nm at the maximum.
Remove the tool used for adjustment.
4. Adjust the control parameters of the posi-
tioner as specified in the corresponding
mounting and operating instructions and,
initialize the positioner.
5. After adjusting the bypass restriction
screw, lead-seal the setting.
5.3.2 Tuning to the control
loop requirements
The bypass setting can be changed, if re-
quired. To do this, change the position of the
bypass restriction screw gradually by half
turns and correct the control parameters of
the positioner accordingly or re-initialize it.
Turning the bypass restriction screw into the
restriction seat
Î
reduces the bypass cross-section, causing
the volume booster to respond more dy-
namically.
Consequences of a too small bypass
cross-section:
− Loop may start to hunt.
Turning the bypass restriction screw out of
the restriction seat
Î
increases the bypass cross-section, caus-
ing the booster dynamic response to be-
come weaker.
Consequences of a too large bypass
cross-section:
− Slow control response
− Actuating times (filling the actuator with
air or venting the actuator) slowed down
considerably