Page 358 - Centrifugal Pumps 2E

Chemical Pumps Metallic and Nonmetallic 323

Driver
The pump shaft is connected directly to the motor by a rigid adjustable
coupling, and in-line motors are used to absorb the axial thrust. If a nor
mal thrust motor is used, then a separate thrust bearing is used within the
support head to absorb the axial thrust.

Level Controls
With chemical sump pumps, the level control is usually encased to pre-
vent the fluid from coming in direct contact with the switching mecha-
nism.

Stilling Tubes
If it is anticipated that swirl or vortexing will exist within the sump, the
level controls are mounted within a stilling tube that indicates the true
level of the liquid within the sump.

Mounting Plates and Pit Covers
These plates are made out of the same base material as the pumps. De-
pending on the size, the pit covers may require reinforcement of steel
angles or channels. These steel pieces are encapsulated so they are not
exposed to the atmosphere.

Processes

Chemical pumps handle a variety of liquids that could be concentrated,
diluted, or just a trace. The concentration could be from 5% to 50% or
the liquid could be in parts per million. Temperature could be hot or cold,
and a pump can be sold to handle maximum, minimum, or normal tem-
perature. The range of temperature could cause thermal shock and can
vary as much as 150°F from the cold to hot application. The rate of activ-
ity of the fluid changes approximately two to three times for each 18°F
change in temperature. The liquids could have either an alkaline or acidic
pH level. Liquids may contain solids that might cause erosion, corrosion,
or settling problems that would result in clogging. The liquid may have
entrained air that would make a reducing solution into oxidation or it
could have inhibitors to reduce corrosion or accelerators to increase cor-
rosion. The impurities could lead to something called discoloration or so-
lution breakdown.
Final pump material selection is a collective decision based on input
from the pump designer, plant operator, material supplier, and available
technical literature.