Page 54 - Know and Understand Centrifugal Pumps

Cavitation

Vane passing \ Vane passing
syndrome. syndrome.
\

Internal recirculation -

cavitation.
lnadecuate NPSHa / ----

also vaporization and
turbulence cavitation.
Fisure 3-4

Figure 34 shows the inside of the pump where cavitation occurs.

Cavitation review

Reviewing the cavitation theme, we observe that the majority of
cavitation is caused or induced by operation and design.
As we’ve discussed, system design is responsible for much of cavitation.
Yet, the maintenance mechanic is responsible for stopping and
preventing cavitation. And certainly, it’s the maintenance mechanic who
has to deal with the results of cavitation, the constant changing of
bearings, mechanical seals, damaged impellers, wear rings and other
pump parts.
Most mechanics have seen the damaged pump parts with the pump
torn apart on the shop table. Almost all mechanics have seen the
scratches, gouges, and track marks of cavitation on the impeller blades
and pump housings. But without understanding and analyzing the
causes of cavitation damage, the mechanic can only install more
bearings and seals, and possibly hide the damage by re-metalizing the
housing and impeller. This is somewhat frustrating for the mechanic,
because he or she will be performing the same repair work in the next
few weeks or months.

Do something about cavitation!!

The worst thing you can do is .... nothing. Do something. Take this
information, go back into your process plant, and you can prevent and
stop the majority of cavitation.