Increasing The Actuator Thrust; Adapting The Travel Range - Samson 3371 Mounting And Operating Instructions

5. Screw the short nuts together with wash-
ers onto the bolts. Observe tightening
torques.
Short bolt
Washer
Short nut
Clamping bolt
Clamping nut
Fig. 6-1: Spring compression
6.1.2 Increasing the actuator
thrust
The thrust can only be increased in actuators
with "stem extends" direction of action. To
achieve this, the springs of the actuators can
be preloaded by up to 25 % of their travel or
bench range.
Example: Preloading is required for a bench
range of 1.4 to 2.3 bar. 25 % of this span is
0.2 bar. Therefore, the signal pressure range
is shifted by 0.2 bar to 1.6 to 2.5 bar. The
new lower signal range value is 1.6 bar and
the new upper signal range value 2.5 bar.
Î Write the new signal pressure range of
1.6 to 2.5 bar on the actuator nameplate
EB 8317 EN
as the operating range with preloaded
springs.
6.1.3
In some cases, the valve and actuator have
different rated travels. Depending on the di-
rection of action, proceed as follows:
Direction of action: actuator stem extends
Always use actuators with preloaded springs
when the valve's rated travel is smaller than
the rated travel of the actuator.
Example: DN 15 valve with 7.5 mm rated
travel and 120 cm² actuator with 15 mm rat-
ed travel; 1.4 to 2.3 bar bench range.
Washer
The signal pressure for half the actuator trav-
el (7.5 mm) is 1.85 bar. Adding it to the
lower signal pressure range value of 1.4 bar
results in a signal pressure of 3.25 bar re-
quired for spring compression. The new low-
er signal range value is 3.25 bar and the
new upper signal range value 4.15 bar.
Î Write the new signal pressure range of
3.25 to 4.15 bar on the actuator name-
plate as the operating range with pre-
loaded springs.
Direction of action: actuator stem retracts
The springs of actuators with "stem retracts"
action cannot be preloaded. When a SAM-
SON valve is combined with an oversized
actuator (e.g. the rated travel of the actuator
is larger than the rated travel of the valve),
only the first half of the actuator's bench
range can be used.
Adapting the travel
range
Start-up
6-3