EB 2183 EN
11
Design and principle of operation
3 Design and principle of oper-
ation
The Type 2403 Safety Temperature Monitor
(STM) with a valve operates without auxiliary
energy and is designed for extended safety
according to DIN EN 14597. The safety
temperature monitor is used to limit the
temperature by closing a SAMSON
Series 43 Valve connected to the safety
thermostat.
The safety temperature monitor mainly con-
sists of a valve and safety thermostat with
capillary tube (8) and bulb sensor (9).
The connection of an additional Type 2430
Control Thermostat (20) converts the safety
temperature monitor (7) into a temperature
regulator with safety temperature monitor
(TR/STM). See Fig. 2.
The valve is closed by a spring mechanism
when the temperature reaches the adjusted
limit, when the capillary tube breaks or
when leakage occurs in the sensor system.
The safety temperature monitor works ac-
cording to the vapor pressure principle. The
temperature of the medium creates a pres-
sure in the temperature sensor (9) which is
proportional to the measured temperature.
This pressure is transferred through the capil-
lary tube (8) to the operating bellows (10)
and converted into a positioning force. The
force is transferred over the pin (11) of the
operating element to the plug stem (4) and
plug (3). The position of the plug determines
the flow rate of the heat transfer medium
across the area released between the seat
(2) and plug.
The safety temperature monitor closes the
valve when the temperature reaches the
adjusted limit temperature. The safety
temperature monitor resets itself
automatically when the temperature has
fallen to a value of approx. 5 K below the
adjusted limit temperature.
Fail-safe position
When the capillary tube ruptures or there is
a leak in the sensor, the spring mechanism
reacts to the reduced system pressure and
the pin of the operating element (11) closes
the valve. The valve cannot be reset. In this
case, the Type 2403 Safety Temperature
Monitor must be replaced.
The adjusted limit temperature must have a
minimum temperature difference of 15 K to
the set point of the temperature regulator.
Note