Gland packings are generally used in common utility service pump such as water, slurry, alkali handling etc. This arrangement is economical. Mechanical seals are used where toxic and precious liquids are handled. In nuclear application these are provided for d2o handling, process liquid, H2S service pumps, acid, condensate etc. If toxic liquid comes in atmosphere that may be hazardous to men and environment. If precious liquid comes in atmosphere due to leakage through stuffing box may occur huge losses. This arrangement is costlier and used in special application pumps.