Fail-Safe Positions; Globe Valve; Three-Way Valve; Versions - Samson 3246 Mounting And Operating Instructions

Design and principle of operation
Tip
We recommend the use of positioners with
integrated diagnostic firmware (see sec-
tion 3.4) for valves used for on/off service.
The partial stroke test included in this soft-
ware helps prevent a shut-off valve normally
in its end position from seizing up or getting
jammed.

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 valve version (globe valve or
three-way valve) and actuator used (see as-
sociated actuator documentation).
3.1.1

Globe valve

Depending on how the compression springs
are arranged in the pneumatic actuator, the
valve has two different 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 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.
3-4
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
3.1.2

Three-way valve

Depending on how the compression springs
are arranged in the pneumatic actuator, the
valve has two different fail-safe positions:
Actuator stem extends (FA)
When the signal pressure is reduced or the
air supply fails, the springs cause port B
(mixing valves) or port A (diverting valves) to
close. The port B or A 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 cause port B
(mixing valves) or port A (diverting valves) to
open. The port B or A closes when the signal
pressure is increased enough to overcome
the force exerted by the springs.

3.2 Versions

Angle valve
The Type 3246 Valve is also available as an
angle valve (special version) on request.
EB 8046 EN