The characteristic feature of self-operated temperature regulators is their compact design, including a sensor, a valve and a capillary tube. Their simple operating principle is based on fundamental mechanical, physical and thermodynamic laws. A temperature control loop with a heat exchanger is shown in Fig.1. When the water has left the heat exchanger and circulates in the domestic hot water loop, its temperature must be kept constant. In the heating loop, a heat transfer medium, e.g. hot water, circulates through the heat exchanger and transfers part of its heat to the domestic hot water loop. If we assume that the temperature of the hot water remains constant, the transferred heat quantity depends on the flow rate. The flow of hot water is adjusted by the self-operated regulator. The sensor measures the temperature of the variable to be controlled and converts the measured value into a travel signal which is used as output variable. The sensor output signal is transmitted via the capillary tube to the valve where the signal changes the position of the plug as required. Temperature regulators obtain their actuating power from the medium to be controlled, so they do not need supply lines or auxiliary devices. This is the most important benefit of self-operated regulators. They keep costs low, while exhibiting high operational reliability.
SAMSON (1999) Temperature Regulators