I recently suggested to a client that it was near time for a desiccant change.  His response was, How do I know the desiccant needs changing  and what impact or improvements new desiccant would make. He also wanted a factory statement on the life span of desiccant in his heatless dryer which in this case is activated alumina. Below is my response to him and I thought it might be beneficial for others as well.

The typical life span on desiccant in a heatless dryer is 3-5 years. Desiccant will typically last longer in a heatless since there is less thermal shock.

I’m not aware of anyone that publishes estimated life span.

The benefits of new desiccant are better dewpoint and lower pressure drop.

The desiccant in a dryer degrades because of attrition (the desiccant rubbing against itself which wears the bead size down), thermal degradation (if the desiccant is in a heated dryer)  and of course if the dryer happens to be installed on a lubricated compressor system then it will go bad much quicker due to oil fouling. Once oil attaches to the desiccant bead, the pores of the bead are coating with oil (which cannot be removed) thus eliminating the desiccants ability to adsorb water vapor.

A good indicator of desiccant condition is to use a portable hygrometer on the downstream airline to see what actual dewpoint is being achieved.

Another indicator that desiccant is going bad is quicker than normal loading on the particulate filter downstream. As the desiccant deteriorates it creates more dust to be blown downstream which is then captured in the particulate filter.

Another check is the differential pressure across the dryer. Determine the clean differential pressure from the manufacturer and then compare that information to the actual Delta P between the dryer inlet and outlet. The higher the differential pressure above factory specifications indicates a worsening desiccant condition. Assure the factory number used for comparison either includes (or does not include the pre & post filters) and check the corresponding pressures for comparison.

The last suggestion is to obtain a desiccant test kit, pull a desiccant sample from the dryer and have it sent for analysis.  However, to assure an accurate test the sample should be pulled from the middle of the desiccant bed which is often difficult and this service usually incurs a charge which is why I suggest it as the last option.