The HD or D Regulator with the “T” Temperature Pilot is used for controlling temperature in various processes and systems, such as Oil Heaters, Ovens, Process Heaters, Vats, Dryers, and Jacketed Kettles. The purpose of the temperature pilot is to control the operation of the temperature regulating valve. A sensing bulb filled with liquid is used as a thermostat to monitor the temperature of whatever is being heated. The sensing bulb is connected to the temperature pilot by a length of capillary tubing. When the sensing bulb is heated the liquid inside expands and in turn expands a bellows inside the temperature pilot. The expansion and contraction of this bellows is what controls the operation of the temperature regulating valve.