Nonmetallic pumps

This type of pump is used to handle abrasive, chemically corrosive, and oxidizing liquids, where conventional pumps would require exotic alloys. The wet end of these pumps is non-metallic or lined and coated, sealing and isolating any metal component. The power end is normal.

Non-Metallic Construction Lined/Coated Metallic wet parts

■ Phenolic Resin ■ Rubber Lined/Coated

■ Carbon/Craphitc

■ Most of these pump designs are back-pullout construction.

■ Some meet complete ANSI specs.

Know and Understand Centrifugal Pumps Magnetic drive pumps

BEARINGS LUBRICATED WITH PROCESS FLUID

BEARINGS LUBRICATED WITH PROCESS FLUID

Figure 6-11

This type of pump utilizes a conventional electric motor that drives a set of magnets that drive other magnets fixed to the pump shaft. A nonmagnetic housing that isolates the pumped liquid from the environment separates the rotating magnet sets. The impeller, the driven magnet set, shaft and bearing assembly all operate inside the pumped liquid. There are two types of magnet drives:

■ Eddy Current electromagnets that can experience some slip inside the pump and may decouple.

■ Rare earth permanent magnets with no slip and not subject to decoupling.

The advantages

■ Considered leak proof (although some models use gaskets and o-rings as secondary seals).

■ No exposure (neither liquid nor gaseous) to workers or the environment.

■ Considered more reliable than canned motor pumps (the containment shell is larger).

The disadvantages

■ Higher initial cost and repair cost.

■ Not good at handling abrasives.

■ Must be operated very close to the BFP on the curve.

■ Cannot resist extended cavitation.

■ The magnets can decouple (requiring stopping and restarting the pump).

■ Not as efficient as conventional pumps.

■ May require larger motors.

■ Tends to heat the pumped liquid.

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