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Design and principle of operation
3.1 Fail-safe action
The fail-safe position of the valve upon sup-
ply air (signal pressure) failure is determined
by how the piston and actuator spring are
arranged in the pneumatic actuator.
Fail-close (FA/NC)
The actuator spring closes the valve upon air
supply failure. The valve opens when the sig-
nal pressure increases.
Fail-open (FE/NO)
The actuator spring opens the valve upon air
supply failure. The valve closes when the sig-
nal pressure increases.
3.2 Versions
Additional actuator spring (changing the
spring force)
Fail-close (FA/NC) valves with the valve siz-
es DN 40 and 50 (NPS 1½ and 2) and with
60 cm² actuators (Ø = 90 mm) can be fitted
with one or two actuator springs (marked on
the nameplate with I or II). See the 'Markings
on the device' section).
By adding a spring or removing the internal
spring, the permissible differential pressure
and associated signal pressure can be
changed.
Actua-
Spring
Version
tor
force
1440 N
60 cm²
FA/NC
2160 N
3-2
Quantity
Signal
of
pressure
springs
1
3.8 bar
2
5.4 bar
Note
It is not possible to change the fail-safe ac-
tion.
3.3 Accessories
− Type 4740 Limit Switch with electric mi-
croswitches to indicate valve OPEN or
valve CLOSED for fail-open or fail-close
version, optionally with 3/2-way sole-
noid valve
− Type 4740 Limit Switch with inductive
proximity switches for fail-open or fail-
close version, optionally with 3/2-way
solenoid valve
− Fixture for holding proximity switches
with M12 thread
− NAMUR adapter to attach a solenoid
valve for valves in DN 15 to 50
− 3/2-way solenoid valve with G
rect attachment to the actuator (double
nipple required for mounting) in DN 1½
− 0 to 12 bar; 24 V DC or 230 V AC, op-
tional silencer
− Double nipple G
brass
− Elbow fitting (order no. 8582-2273) for
valves in DN 65 and 80
3.4 Additional fittings
Strainers
We recommend installing a SAMSON
strainer upstream of the valve. It prevents sol-
for di-
1
/
8
x G ¼ detachable,
1
/
8
EB 8140 EN
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