4A Molecular sieve is an alkali alumino-silicate. It is the sodium form of the Type A crystal structure and has an effective pore opening of 4 angstroms. It is used to dehydrate air and gases. Molecular sieves are regenerated by heating and purging. Regeneration temperatures must be 400° to 600° F but are not to exceed 1000° F. The degree of regeneration depends on the temperature reached in purge.