Danfoss STM (065-0609) — self-acting safety temperature monitor, PN 25. The STM is a self-acting safety temperature monitor working on the liquid-expansion principle: the temperature sensor, capillary tube and bellows are liquid-filled, and on rising temperature the liquid expands and closes the valve, protecting the system against exceeding temperatures. It is type-tested to EN 14597 (STW 871). It comprises a temperature sensor (210 mm × Ø16 mm), a 5 m capillary tube and a bellows element; the sensor is fitted into the pipe via a sensor pocket with connection M22x1 / R 3/4 ext. thread acc. DIN 2999. Fixed limit-temperature setting range 20 – 75 °C. Gain Ks 0.3; time constant 100 s; maximum media temperature at the sensor 125 °C; ambient temperature 0–70 °C. Mounts on Danfoss AVQT / AVQMT flow-and-temperature controllers and VGS steam valves (and combines with an AVT actuator on STM/AVT/VGS arrangements) for over-temperature safety in district-heating, hot-water and steam systems up to 200 °C. Temperature sensor and impulse (capillary) tube Copper (mat. No. 2.0090); sensor pocket Brass. Type test DIN EN 14597:2005-12 STW871. Sensor connection M22x1 / R 3/4 ext. thread acc. DIN 2999. OEM P/N 065-0609. EAN 5702421544310. Technical data quoted verbatim from store.danfoss.com (code 065-0609) and the Danfoss "Temperature controller AVT with safety temperature monitor STM / VGS (PN 25)" data sheet.