Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Mechanical Seals 379
Figure 17-19. Full convolution elastomeric bellows with single spring construction
(courtesy of John Crane).
seals that use an O-ring, wedge, or V-ring. Typical construction is illustrated
in Figure 17-12.
Non-pusher seals are defined as seal assemblies in which the secondary
seal is not forced along the shaft by the mechanical load or hydraulic
pressure in the stuffing box. Instead, all movement is taken up by the
bellows convolution. A non-pusher design is shown in Figure 17-19.
This definition applies to those seals that use half, full, and multiple convolution
bellows as a secondary seal.
Materials of Construction
The selection of materials of construction must be based on the operating
environment for the seal. The effects of corrosion, temperature, deformation
from pressure, and wear from sliding contact must be considered
for good life. Each seal must be broken down into component parts
for material selection. The effects of corrosion must be known for the
secondary seal, primary and mating rings, as well as hardware items.
The NACE (National Association of Corrosion Engineers) corrosion
handbook is an excellent source of information for corrosion rates of various
materials in a wide variety of liquids and gases. When hardware
items of a seal are exposed to a liquid and the corrosion rate is greater
than 2 mils per year, a double seal arrangement should be considered.
The metal parts in this seal arrangement can be kept out of the corrosive