Page 249 - Know and Understand Centrifugal Pumps

Avo i d i n g We a r

in Centrifugal

Pumps

Introduction

In the moment of starting a new pump, that pump is headed for the
day when it will need repair even if the design and operation is correct.
One factor that determines the repair is internal wear. Imagine an ideal
application where the pump is operating at its BEP and the system is
stable. Does this condition ever exit? If you answer yes, you are one of
fortunate few. However at some point, even if it does not break, the
pump will go to the shop because of internal wear. This chapter
presents different sources of internal wear and suggestions to extend
the useful running time of the pump.

Erosion

Erosion is the wear of the pump internal parts by suspended solid
particles contained in the fluid being pumped. The most affected parts
are: wear rings, shaft sleeves, packing, mechanical seal faces, lip seals,
the pump casing and the impeller.

Erosion can be caused by small particles not visible to the human eye,
like dissolved minerals in ‘hard water.’ Larger solids like sand, boiler
scale, and rust can also cause serious erosion inside the pump.

The fluid being pumped is often not well defined. Terminology like
well water, industrial effluent, raw water, boiler feed water, condensate
water, etc., is usually the only definition we have of the fluid being
pumped. Any of these fluids can contain several concentrations of solids
that cause erosion and wear inside the pump.
When the liquid being pumped is known to have a large concentration
of solids, the materials inside the pump should be changed to more