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

Note
Actuators that have already been preloaded
by SAMSON without mounting the valve are
labeled correspondingly.
Additionally, these actuators can be identi-
fied by long bolts with nuts protruding from
the bottom diaphragm case. They allow the
spring compression to be relieved evenly
when disassembling the actuator (see sec-
tion 9.3).
5.3.1 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 signal
pressure range of 1.4 to 2.3 bar. 25 % of
this span corresponds to 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 pressure range value is 1.6 bar and
the new upper signal pressure range value
2.5 bar.
Î Write the new signal pressure range of
1.6 to 2.5 bar on the actuator nameplate
as the operating range with preloaded
springs.
EB 8317 EN
5.3.2 Adapting the travel
range
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.
The signal pressure for half of the actuator
travel (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 preloading the springs. The new
lower 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
SAMSON valve is combined with an over-
sized 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.
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.
Mounting and start-up
29