Stuffing Box:

In the whole centrifugal pumps, the rotating shaft which drives the impeller penetrates the pressure boundary of the pump casing. It is significant in which the pump is designed properly to control the amount of liquid that leaks along the shaft at the point which the shaft penetrates the pump casing. There are several variant methods of sealing the shaft penetration of the pump casing. Factors measured while selecting a method involve the pressure and temperature of the fluid being pumped or the size of the pump, and the chemical and physical features of the fluid being pumped.

One of the easiest categories of shaft seal is the stuffing box. A stuffing box is a cylindrical space within the pump casing surrounding the shaft. The Rings of packing material are placed in this space. Packing is material within the form of rings or strands which is placed in the stuffing box to form a seal to control the rate of leakage along the shaft. The packing rings are held in place through a gland. The gland is, in turn, held in place through studs along with adjusting nuts. Since the adjusting nuts are tightened then they move the gland in and compress the packing. This axial compression causes the packing to expand radially, outline a tight seal among the rotating shaft and the within wall of the stuffing box.

The high speed rotation of the shaft produces an important amount of heat as it rubs against the packing rings. If no lubrication and cooling are given to the packing, the temperature of the packing rises to the point whereas damage occurs to the packing, the pump shaft, and probably nearby pump bearings. Stuffing boxes are generally designed to permit a small amount of controlled leakage along the shaft to gives lubrication and cooling to the packing. The leakage rate could be adjusted through tightening and loosening the packing gland.