Rusty Pump Rotors: Should you Replace or Resurface?

March 16, 2018

Pump reconditioning specialists are used to asking tough questions. This newest one, the decision to recommend a replacement rotor or a resurfacing operation, is harder to answer than most. Fundamentally, the solution can't be issued with any insurance until the rotor has been properly checked. How bad is the oxidizing effect? If the marring is surface deep, then the reconditioning process commences. And yet, what if the damage cuts deeper?

Sounding Out Rotor Geometry

Crest-to-crest measurements define the initial properties of this specialized drive shaft. If that value proves one thing, it's the fact that this mechanism has a dimensionally precise form. If the base metal is rusty, there's every chance of a recovery. But, and this point is important, that recovery cannot be secured if the base metal is heavily eroded. Fortunately, rusty pump rotors tend to oxidize evenly. In this case, the resurfacing work scrubs away the stain so that a new layer of double-plated chrome or nickel can then be applied.

Anticipating Fluid Pocket Corruption

The interference fit between the rigid helical rotor and the elastomeric stator ensures shear-less fluid conveyance. If those fluid packets break down, the stator is probably on its way out. However, rusty pump rotors also cause this flow-compromising problem. The corrosion occurs when the protective coating wears away. It begins as that salvageable stain, a blemish that can be scrubbed away without too much effort. Sometimes, unfortunately, the cleaning task reveals more damage. The geometry of the rotor has been subtly altered by a pitted area. The honeycombed patch invalidates the smooth geometry. It's too worn, too materially subtracted to correct. This time around, the only choice is a replacement rotor.

Identifying Stain Fingerprints

Plain old rust is observed as a brown/orange stain. In this instance, some abrasive stream has worn away the protective coating. Oxidizing water has gone to work on the base metal. Next, aggressive chemicals cause pitting. Unfortunately, many food-based processing sites do convey vinegary streams and acidic fruit juices, so this aggressive attack occurs on a regular basis. Finally, even those thin layers of rust are likely to permanently damage this rigid pump component, especially when they're left to their own devices. The oxidized metal is weak. It will spread and gather more scrapes, then those small scrapes will develop into large grooves.

Small scrapes can be buffed out so that the reconditioned rotor can enter service once more. If they've deepened into geometry-altering scrapes, again, the only course of action is a pump rotor replacement. Avoid those accumulating scrapes, and the costly replacement work, by initiating a preventative maintenance program.

Contact Alpha Pumps:

Phone:    (03) 9311 7188
Fax:          (03) 9364 9554
Mobile:    0403 030 830

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