The simplest form of a desiccant kind of gas or air dryer is the heatless compressed one. It can achieve a dewpoint of -40°C for the compressed air systems as well as the other applications of gas and/or air dryers. After passing through the pre-filter, the wet incoming compressed air passes thorugh the assembly of the slide piston.

Next, this air is directed towards the first chamber wherein it travels upwards through the desiccant bed consisting of activated alumina or molecular sieves. This causes it to dry up due to the adsorption effect of the bed. The dry compressed air coming out of the first chamber now travels through the assembly of check valves hence paving its way through the alter-filter and thereby to the area of application or work.

The desiccant in the second chamber that had been wetted in the previous cycle regenerates simultaneously as the compressed air dries in the first chamber. The purge valve depressurizes the second chamber down to the atmospheric pressure in the downward direction.

Meanwhile, a portion of the dry compressed air flushes the desorbed moisture out by passing through the needle valve or orifice plate through the desiccant. The purge valve closes and the tower slowly re-pressurizes to line pressure ensuring a smooth changeover as the regeneration completes. An effective dewpoint of -40°C or even better is obtained at atmospheric pressure with an additional period of 5 minutes for drying. An approximate of 60 seconds is all the re-pressurization takes in the regeneration process. This is the principle involved in heatless air dryer manufacturing.