In some situations, packing material is not adequate for sealing the shaft. One common
alternative method for sealing the shaft is with mechanical seals. Mechanical seals
consist of two basic parts, a rotating element attached to the pump shaft and a stationary
element attached to the pump casing. Each of these elements has a highly polished
sealing surface. The polished faces of the rotating and stationary elements come into
contact with each other to form a seal that prevents leakage along the shaft.
The important information in this chapter is summarized below.
Centrifugal Pumps Summary
The impeller contains rotating vanes that impart a radial and rotary motion to the
The volute collects the liquid discharged from the impeller at high velocity and
gradually causes a reduction in fluid velocity by increasing the flow area, converting
the velocity head to a static head.
A diffuser increases the efficiency of a centrifugal pump by allowing a more gradual
expansion and less turbulent area for the liquid to slow as the flow area expands.
Packing material provides a seal in the area where the pump shaft penetrates the
Wearing rings are replaceable rings that are attached to the impeller and/or the
pump casing to allow a small running clearance between the impeller and pump
casing without causing wear of the actual impeller or pump casing material.
The lantern ring is inserted between rings of packing in the stuffing box to receive
relatively cool, clean liquid and distribute the liquid uniformly around the shaft to
provide lubrication and cooling to the packing.