Design And Principle Of Operation; Fail-Safe Positions - Samson 3251 Mounting And Operating Instructions

Design and principle of operation

3 Design and principle of oper-
ation
The single-seated Type 3251 Globe Valve is
preferably combined with a SAMSON
Type 3271 or Type 3277 Pneumatic Actuator
(see Fig. 3). It can also be combined with
other actuators.
The body (1) is designed either with flanges
or welding ends (optionally with additional
welding-neck ends). The seat (4) and plug
(5) are installed in the body. The plug stem is
connected to the actuator stem (A7) by stem
connector clamps (A26) and sealed by an
adjustable packing (15). This packing
(Form MS) is specially designed for molten
salt service and has an additional zinc-im-
pregnated coating to protect against corro-
sion and prevent leakage. The valve can be
fitted with a bellows seal (22) to allow it to
withstand high temperatures up to 580 °C.
In this version, a test connection (42) on the
bonnet (2) allows leakage monitoring.
The springs (A10) in the pneumatic actuator
are located either above or below the dia-
phragm (A4) depending on the selected fail-
safe action (see section 3.1). A change in
the signal pressure acting on the diaphragm
1 Body
2 Bonnet
3 Yoke
4 Seat
5 Plug
8 Threaded bushing
(packing nut)
9 Stem connector nut
10 Lock nut
14
causes the plug to move. The actuator size is
determined by the diaphragm area.
The medium flows through the valve in the
direction indicated by the arrow. A rise in
signal pressure causes the force acting on
the diaphragm in the actuator to increase.
The springs are compressed. Depending on
the selected direction of action, the actuator
stem retracts or extends. As a result, the plug
position in the seat changes and determines
the flow rate through the valve.
Molten salt
Molten salt is used in heat recovery plants
instead of organic heat transfer oils. Molten
salt remains liquefied at temperatures up to
almost 600 °C. It is neither flammable nor
toxic. It has a higher heat capacity than con-
ventional heat transfer media.
An exact temperature control and monitoring
of molten salt is essential since it solidifies
very quickly as it cools down. For this pur-
pose, the bonnet (2) of the valve is designed
with a connection for a temperature sensor.

3.1 Fail-safe positions

The fail-safe position depends on the actua-
tor used.
14 Body nut
15 Packing
17 Body gasket
22 Bellows seal
37 Plug stem with bellows
42 Test connection
84 Travel indicator scale
92 Castellated nut
A4 Diaphragm
A7 Actuator stem
A8 Ring nut
A10 Spring
A16 Vent plug
A26 Stem connector clamps
S Signal pressure connection
EB 8052-1 EN