TEMPERATURE CONTROL SYSTEM

The temperature control system consists of a controller (Fig. 1), an actuator (Fig. 2), a 3-way valve (Fig. 3, and a thermometer (Fig. 4).

Figure 2. UE controller for hot oil.

Figure 3. Apollo valve actuator.

Figure 4. Hot oil valve.

Figure 5. Capillary bulb and dial thermometer.

The 3-way valve has two positions. In one position it diverts hot oil through the heating coils of the asphalt tank. In its other position it bypasses the hot oil so that it does not flow through the heating coils.

The valve (Fig. 4) is electrically-powered by an Apollo actuator (Fig. 5), and has two positions. Each position corresponds to one of the two positions of the actuator. The actuator is controlled by a UE controller (Fig. 2), which has a capillary tube (Fig. 5) that senses the temperature of asphalt. The controller activates the actuator, which rotates the valve to divert hot oil to the coils when the temperature of the asphalt is lower than the set point of the controller.

The UE controller has either two or three pointers. The black pointer always indicates the temperature of the asphalt inside the tank. The red pointer enables the operator to set a temperature or set point, which is the desired temperature for the asphalt.

The green pointer is only on controllers for asphalt tanks that have mixers. This pointer is used to set the asphalt temperature at which you want the mixer to shut off. This pointer should be set to shut off the mixer at temperatures of 300 degrees F (minimum) to avoid overloading or damaging the mixer from asphalt that has thickened or begun to solidify.

To check the green pointer for proper operation, make sure the asphalt is at least 300 degrees F. Set green pointer lower than black pointer and turn on mixer. The mixer should operate normally. With mixer running, reset the green pointer higher than black pointer. The mixer should shut off and the mixer alarm should sound. After test, reset all controls to their normal condition.

The capillary bulb of the UE controller is installed in a pipe called a “dry well.” A conventional dial thermometer (Fig. 5) is also installed in a dry well next to the one where the capillary tube is installed. The dial thermometer is for backup so you can double-check the temperature indications of the UE controller.

Incidentally, a dry well is a pipe welded into the wall of the asphalt tank. It protrudes into the liquid asphalt, but is capped so that no asphalt enters the pipe (hence the name “dry well”). The other end of the pipe protrudes out of the tank. The capillary temperature sensing bulb of the temperature controller is installed in the external end the pipe. The pipe is partially filled with heat transfer oil to ensure efficient transfer of heat from the liquid asphalt inside the tank to the sensing bulb. The same is true for the dial thermometer.

You should periodically remove both the capillary bulb and the dial thermometer to make sure that the pipe is partially filled with heat transfer oil. Without the heat transfer oil in the dry well, these devices will not respond reliably or consistently. Do not over tighten the fittings that secure the bulb and dial thermometer. On dial thermometers, do not grip face of dial for tightening. Instead, use a wrench on the hex fitting.

To check for proper operation of the temperature control system first check that the temperature pointer of the UE controller is within 5 degrees of the dial thermometer. If not, you may need to either replace the dial thermometer or recalibrate the UE controller. Please refer to applicable Heatec documents on recalibrating UE controllers listed above.

If the power-operated valve is presently diverting hot oil to heat the tank, reset the set point on the UE controller to a temperature lower than the current temperature. The valve should respond by shutting off hot oil to the tank.

If the power-operated valve is not presently diverting hot oil to heat the tank, reset the set point on the UE controller to a temperature higher than the current temperature. The valve should respond by diverting hot oil to heat the tank.

Reset all controls to their normal condition.