Samson 3321 - Fail-Safe Positions; Mounting Types

16 EB 8111/8112 EN
Design and principle of operation
Table1: Possible combinations and types of attachment
Actuator Type of attachment
Type3371 Actuator area 120cm² 350cm²
For valve size
DN15 to 50/NPS½ to 2 FormB ––
DN65 to 100/NPS2½ to 4 FormC FormC
Type3372 Actuator area 120cm² 350cm²
For valve size
DN15 to 50/NPS½ to 2 Form B –
DN65 to 100/NPS2½ to 4 – Form C
Type3374 Form-t attachment using stem connector and yoke
Type5824 Form-t attachment using stem connector and yoke
3.1 Fail-safe positions
Upon failure of the air supply or power sup-
ply, the valve moves to its fail-safe position.
− Actuator stem extends (fail-close): upon
power supply or air supply failure, the
actuator stem extends causing the valve
to close.
− Actuator stem retracts (fail-open): upon
power supply or air supply failure, the
actuator stem retracts causing the valve
to open.
The direction of action of the electric and
electropneumatic actuators is determined by
the actuator version.
The direction of action of the Type3371
Pneumatic Actuator can be reversed, if re-
quired. See the mounting and operating in-
structions uEB8317.
3.2 Mounting types
There are two different types of attachment
to mount the pneumatic or electropneumatic
actuator onto the valve depending on the
version (valve size etc.): mounting using
crossbeam or mounting using rods (see
Table1).
1. Mounting using crossbeam and central
nut
When the actuator is mounted to the
valve using a crossbeam (Form B, Fig.6),
the actuator is fastened to the valve bon-
net using a central nut.
2. Mounting using rods
When the actuator is mounted on rods
(Form C, Fig.7) the actuator is connect-
ed to the valve bonnet using rods. In this
case, a crossbeam is not required for
mounting the actuator. A plate keeps the
correct distance between rods.
When an electric actuator is mounted onto
the valve, it is mounted with a form-t con-
nection using a stem connector and yoke.
Note