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

414 Centrifugal Pumps: Design and Application
Figure 17-52. Small hot spot on a seal face.
porizes, the seal will open, cooling the spot which results in heat checking
of the surface. When removed from the equipment after running for a
short period of time, the deformed surface may measure between 5 to 10
micro-inches larger than the surrounding surface. In operation, however,
due to the developed heat at the hot spot, the deformed surface will appear
to be larger than the lubricating film. If this seal is allowed to run
with this type of surface condition, the liquid being sealed will continue
to flash and vaporize. Carbonized debris from the liquid being sealed
and/or carbon wear particles from the seal faces will begin to build up on
exterior surfaces of the seal parts as illustrated in Figure 17-53. The
flashing or vaporization of the liquid being sealed may be heard above
the normal equipment sounds as a spitting or sputtering sound that may
occur every few seconds to several minutes. This type of condition indicates
abnormal wear occurring from the damaged mating ring. If a seal is
believed to be operating in an unstable condition, it may be checked for
sound as well as for the amount of carbonized debris on the exterior surfaces
of the gland plate. Eliminating hot patches of thermally distressed
material from instability can be achieved through increased cooling direct
to the seal faces. If this is not possible, then the seal manufacturer
should be contacted to determine whether or not hydropads could be incorporated
into the seal design. Thermal distressed or heat checked seal
faces commonly occur when a seal is run in liquids that are exceptionally