Each dryer should be trapped individually to prevent flooding. Syphon drainage is standard practice. Condensate moving up the syphon from the outer rim to the center of the drum is subject to reheating and flashing. Therefore, steam traps must have hot discharge and fast response with the ability to handle flash steam by means of a small bleed passage. Air venting capability is an important requirement during start-up when drums or cylinders contain large amounts of air.
Thermodynamic traps are phase detectors in that they can discriminate between condensate and steam.
The working principle is simple and, with only one moving part, these devices are small and rugged. There are three basic types of thermodynamic traps which differ from one another by the configuration of the valve they use to open and close a port. Each is well-adapted to a particular set of service conditions. The main thermodynamic feature that is desirable in process applications is the hot-running design and responsiveness to load changes. Thermodynamic traps also handle air very well, which is essential to an efficient heat transfer rate.