Pumps must be in top order to keep terminals operating efficiently under even the most challenging conditions

Proactive steps in both preventive and protective maintenance can keep the pumps running reliably in environments that challenge the effective operation of the product handling system. It is important to remember that product transfer system is under constant threat.

Centrifugal pumps move liquids through the use of centrifugal force. The three common styles of centrifugal pumps are:

• ANSI — These pumps meet centrifugal-pump manufacturing criteria established by the American National Standards Institute (ANSI) in 1977. With that standard in mind, ANSI centrifugal pumps are engineered for operational flexibility and durability, and can meet the needs of virtually any fluid-transfer application.

• Standard End-Suction — Ideal for thin liquids and the top choice for most water-pumping applications.

• Self-Priming — Balanced pumping pressures prevent product recirculation, making these pumps ideal for high-capacity loading and unloading operations.

No matter the operating conditions or specific type of pump, a routine maintenance program will extend pump life. Well-maintained equipment simply lasts longer and requires fewer and less-expensive repairs.

A detailed record of any preventive maintenance that was performed and repairs that were needed should be kept in order to help diagnose problems and eliminate, or minimize, any future equipment downtime. Routine preventive and protective maintenance practices should, at a minimum, include the monitoring of:

• Bearing and lubricant condition. Monitor bearing temperatures, lubricant level and vibration. The lubricant should be clear with no signs of frothing, while changes in bearing temperature may indicate imminent failure.

• Shaft seal condition. Mechanical seals should show no signs of visible leakage. Any packing should leak at a rate of about 40 to 60 drops per minute.

• Overall pump vibration. Imminent bearing failure can be preceded by a change in bearing vibration. Unwanted vibration can also occur due to a change in pump alignment, the presence of cavitation or resonances between the pump, its foundation or the valving located in the suction and/or discharge lines.

• Pump discharge pressure. The difference between the readings on the suction and discharge gauges will provide the total developed head pressure of the pump. A gradual decrease in the developed head pressure of the pump can indicate that the impeller clearance has widened, which requires an impeller clearance adjustment to restore the pump's intended design performance.

To stay on top of these potential maintenance concerns, Griswold Pump Company, a centrifugal-pump manufacturer, suggests the following basic maintenance regimen. Maintenance and monitoring intervals should be shortened if the pump is used in severe-service conditions, such as with highly corrosive liquids:

Quarterly maintenance

• 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, mechanics should regrease bearings every three months or 2,000 operating hours, whichever comes first

• Check the shaft alignment

• Regrease motor bearings according to manufacturer instructions

Annual maintenance

The pump's performance should be checked and recorded in detail at least once a 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 assessment of a pump's performance is made, any changes in the benchmarks should be noted and used in determining the level of maintenance that may be required to get the pump back to 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, particular attention needs to be paid to bearing lubrication in order 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 mid-point 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 indication that a water content — which is commonly the result of condensation — of greater than 2,000 ppm is present. If this is the case, the oil needs to be changed immediately.

If the pump is equipped with regreaseable bearings be certain to never mix greases of differing consistencies or types. Also note that the shields must be located toward the interior of the bearing frame. When regreasing, ensure that the bearing fittings are absolutely clean as any contamination will decrease bearing life. Over greasing must be avoided as this can cause localized high temperatures in the bearing races and create caked solids. After regreasing, the bearings may run at a slightly higher temperature for a period of one to two hours.

In instances where a terminal operator may need to replace a part, or parts, on a malfunctioning pump, this repair operation should 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. Inspect lubrication passages to be sure that they are open.

• Shaft and Sleeve — Visually inspect for grooves or pitting. Check 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 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, warpage 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 of these maintenance recommendations may seem daunting, but it is only through a routine such as this that a fluid-handling operation can maximize the service life of the equipment while enhancing the safety of plant personnel and the environment.

Rick Whidden is applications manager for Grand Terrace, California-based Griswold Pump Company, an operating company within Pump Solutions Group (PSG). He can be reached at (800) 843-9222 or [email protected]. PSG is a member of Dover Corporation and comprised of seven leading pump brands — Wilden, Blackmer, Griswold, Neptune, EnviroGear,
Almatec, and Mouvex. ♦