- Check the pump's foundation and hold-down bolts for tightness.
- For oil-lubricated pumps, the oil should be changed after the first 200 hours of operation for a new pump then after every three months or 2,000 operating hours, whichever comes first. For grease-lubricated pumps, the bearings should be re-greased every three months or 2,000 operating hours, whichever comes first.
- Check the shaft alignment.
- Re-grease the motor bearings according to the manufacturer's instructions.
The pump's performance should be checked and recorded in detail at least once per year. Performance benchmarks should be established during the early stages of a pump's operation when the parts are new and the installation adjustments are correct. This benchmarking data should include:
- The pump's developed head pressure as measured at the suction and discharge gauges
- Pump flow rate
- Motor amp draw
- Vibration signature
When the annual pump performance assessment is conducted, any changes in the benchmarks should be noted and used to determine the level of maintenance that may be required to get the pump operating at its efficient best.
When considering centrifugal-pump operation and maintenance requirements, one thing must be kept in mind: all pump bearings will fail eventually. However, the cause of bearing failure is more often than not a failure of the lubricating medium not equipment fatigue. Therefore, bearing lubrication requires particular attention to maximize bearing and, by extension, pump life.
If oil is being used for bearing lubrication remember to use only non-foaming and non-detergent oils. The proper oil level is at the midpoint of the bull's-eye sight glass on the side of the bearing frame. It is important to avoid over-lubrication as it can be just as damaging as under-lubrication since excess oil will cause a slightly higher horsepower draw and generate additional heat, which can cause frothing of the oil.
When checking the condition of the lubricating oil, if any cloudiness is observed, it can be an indication that water content—which is commonly the result of condensation—of greater than 2,000 parts per million is present. If this is the case, the oil must be changed immediately.
If the pump is equipped with re-greaseable bearings, be certain never to mix different grease consistencies or types. Also note that the shields must be located toward the interior of the bearing frame. When re-greasing, ensure that the bearing fittings are absolutely clean as any contamination will decrease bearing life.
Overgreasing must also be avoided because this can cause localized high temperatures in the bearing races and create caked solids. After re-greasing, the bearings may run at a slightly higher temperature for a period of one to two hours.
For instances in which a terminal operator may need to replace a part or parts on a malfunctioning pump, these circumstances should also be treated as an opportunity to examine the pump's other parts for signs of fatigue, excessive wear and cracks. At this time, any worn parts should be replaced if they do not meet the following part-specific tolerance standards:
- Bearing frame and foot—Visually inspect for cracks, roughness, rust or scale. Check machined surfaces for pitting or erosion.
- Bearing frame—Inspect tapped connections for dirt. Clean and chase threads as necessary. Remove all loose or foreign material, and inspect lubrication passages to be sure that they are open.
- Shaft and sleeve—Visually inspect for grooves or pitting. Check the bearing fits and shaft runout, and replace the shaft and sleeve if worn or if the shaft runout is greater than 0.002 inches.
- Casing—Visually inspect for signs of wear, corrosion or pitting. The casing should be replaced if wear exceeds 1/8-inch deep. Check gasket surfaces for signs of wear or irregularities.
- Impeller—Visually inspect the impeller for wear, erosion or corrosion damage. If the vanes are worn more than 1/8-inch deep or if they are bent, the impeller should be replaced.
- Frame adapter—Visually inspect for cracks, warping or corrosion damage, and replace if any of these conditions are present.
- Bearing housing—Visually inspect for signs of wear, corrosion, cracks or pits. Replace housings if worn or out of tolerance.
- Seal chamber/stuffing box cover—Visually check for cracks, pitting, erosion or corrosion, paying special attention to any wear, scoring or grooves that might be on the chamber face. Replace if worn more than 1/8-inch deep.
- Shaft—Check the shaft for any evidence of corrosion or wear. Check the shaft for straightness, noting that the maximum total indicator reading (TIR) at the sleeve journal and coupling journal cannot exceed 0.002 inches.
Implementing all these maintenance recommendations may seem daunting, but through a routine such as this, a fluid-handling operation can maximize the service life of the equipment while enhancing the safety of plant personnel and the environment.