Fail-Safe Action; Versions; Additional Fittings - Samson EB 8075 EN Mounting And Operating Instructions

3.1 Fail-safe action

The fail-safe position of the control valve up-
on air supply or control signal failure de-
pends on the actuator used (see associated
actuator documentation).
Depending on how the compression springs
are arranged in the SAMSON Type 3271
Pneumatic Actuator, the valve has two differ-
ent fail-safe positions:
Actuator stem extends (FA)
When the signal pressure is reduced or the
air supply fails, the springs move the
actuator stem downward and close the
valve. The valve opens when the signal
pressure is increased enough to overcome
the force exerted by the springs.
Actuator stem retracts (FE)
When the signal pressure is reduced or the
air supply fails, the springs move the
actuator stem upwards and open the valve.
The valve closes when the signal pressure is
increased enough to overcome the force
exerted by the springs.
Tip
The actuator's direction of action can be re-
versed, if required. Refer to the mounting
and operating instructions of the pneumatic
actuator:
EB 8310-X for Type 3271
u
A double-acting piston actuator does not
have a defined fail-safe action as it does not
contain a spring assembly.
EB 8075 EN
Design and principle of operation

3.2 Versions

With insulating section/bellows seal
The modular design allows an insulating sec-
tion or bellows seal to be fitted to the stan-
dard valve version.
Actuators
In these instructions, the preferable combina-
tion with a Type 3271 Pneumatic Actuator or
a piston actuator is described. The pneumat-
ic actuator (with or without handwheel) can
be replaced by another pneumatic actuator
in a different size, but with the same travel.
Î Observe the maximum permissible actu-
ator force.
Note
If the travel range of the actuator is larger
than the travel range of the valve, the spring
assembly in the actuator must be preloaded
so that the travel ranges match. See associ-
ated actuator documentation.
The basic pneumatic actuator can be re-
placed by an actuator with additional hand-
wheel, an electric actuator or an hydraulic
piston actuator.

3.3 Additional fittings

Strainers
We recommend installing a SAMSON
Type 2 Strainer upstream of the valve. It pre-
vents solid particles in the process medium
from damaging the valve.
3-5