Fail-Safe Positions; Versions; Additional Fittings - Samson 3291 Translation Of Original Instructions

3.1 Fail-safe positions

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
and Type 3277 Pneumatic Actuator, the
valve has one of two different fail-safe posi-
tions:
− 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 over-
come 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 over-
come 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:
u EB 8310-X for Type 3271 and Type 3277
EB 8072 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 SAMSON Type 3271 or
Type 3277 Pneumatic Actuator is described.
The pneumatic 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 a pneumatic actuator with addi-
tional handwheel or by an electric actuator
(see Information Sheet u T 8300).

3.3 Additional fittings

Strainers
We recommend installing a SAMSON
strainer upstream of the valve. It prevents sol-
id particles in the process medium from
damaging the valve.
3-3