Samson Type 3766, Mounting And Operating Instructions

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4.1.1 Adjusting the proportional
band Xp and air delivery Q
1. Close the volume restriction Q (11) as
far as the required positioning speed
permits. To check, push the diaphragm
lever (3) as far as it will go.
2. Adjust the reference variable at the
input to approx. 50 % of its range.
3. Turn the zero adjuster (6.2) until the
valve has reached approx. mid-travel.
4. Use the adjuster (8) to set the propor-
tional band X
p
to a medium value
(1/2 turn).
5. Check the valve’s tendency to hunt and
the positioning speed by briefly tapping
the diaphragm lever (3). The X
p
value is
to be adjusted to be as small as
possible, yet avoiding that considerable
overshooting occurs.
Important!
Always adjust the Xp restriction before set-
ting the starting point. Later modifications
cause the zero point to shift.
4.1.2 Adjusting the actuator: "Actu-
ator stem extends"
Important!
To ensure that the valve can be closed with
full force, fully vent the diaphragm chamber
when the reference variable reaches its
lower (operating direction <<) and upper
(operating direction <>) value.
As a result, adjust the input signal to a
slightly increased starting point of 0.23 bar
for direct operating direction <<; for reverse
operating direction <>, adjust the input sig-
nal to a slightly reduced starting point of
0.97 bar.
Starting point (e.g. 0.23 bar)
1. Use the pressure adjuster to set the
input signal to 0.2 bar.
2. Turn the zero adjuster (6.2) until the
valve just starts to move from its initial
position.
3. Shut off the input signal and slowly in-
crease it again. Check whether the
valve start to move at exactly 0.23 bar.
Correct any deviation on the zero adjus-
ter (6.2).
Upper range value (e.g. 1 bar)
1. Once the starting point has been set, in-
crease the input signal to 1 bar using
the pressure adjuster. At exactly 1 bar,
the plug stem must stand still, having
passed through 100 % travel (watch the
travel indicator at the valve).
If the upper range value is incorrect,
turn the span adjuster (travel). Four
turns correspond to a travel change of
10 % in standard operation.
32
EB 8355-1 EN
Adjusting the positioner at the valve