The Maintenance Solution
Three types of pump exist which employ centrifugal force to move liquids:
- The first type, ANSI pumps, are named after the American National Standards Institute, which in 1977 established standards for the pumps. These are designed for use in almost any kind of fluid transfer.
- The second type use standard end-suction, and are best for thin liquids. This type is preferred for water pumping.
- The third type are self-priming pumps. With balanced pumping pressures to keep liquids from recirculating, these are ideal for high-capacity work, including loading and unloading of liquids.
One thing shared by all three types of pump is the need for routine maintenance to extend the product's lifespan. This reduces the frequency both of repairs and costly replacement of the pumps. Part of a maintenance routine should include record keeping to aid in the diagnosis of problems in the event of future repair needs.
Basic maintenance routines must include the following:
- Bearing temperatures, lubricant level and vibration of the pump must be monitored to ensure that lubricant is clear and without frothing. Temperature changes can mean failure of the pump is likely in the immediate future.
- Regular inspection of shaft seal for leaks is important; there should be no visible leaking. Packing may leak at 40-60 drops per minute.
- Bearing failure can be predicted by changes in vibration of the pump overall, so this should be carefully watched. Additionally, vibration can happen because of changed pump alignment, cavitation and resonances between the foundation and the pump, or at the valving in the discharge and suction lines.
- The developed head pressure of the pump, given by the difference between the suction and discharge gauge readings, must also be monitored. If the developed head pressure drops slowly over time, this may mean a widening of the impeller clearance, requiring changes to the impeller clearance to keep the pump working within ideal ranges.
Every three months the following maintenance should be performed, with the caveat that extreme conditions (highly corrosive liquid use, e.g.) require more frequent inspections:
- Inspect pump's foundation and make sure hold-down bolts are still tight.
- Oil-lubricated and grease-lubricated pumps require slightly different treatment. Oil-lubricated pumps should have an oil-change after the initial 200 hours of service when new, and every 2,000 operating hours (or three months, whichever comes first). Grease-lubricated pumps have bearings that should be re-greased every three months or after 2,000 hours.
- Shaft alignment should be checked at least once every three months.
- Following manufacturer instructions by re-greasing motor bearings every three months.
Every year the overall operation of the pump should be evaluated and documented annually. This should be done according to baseline data established at the beginning of the pump's service life. This data must include:
- Developed head pressure, taken from suction and discharge gauges as outlined above.
- Pump flow rate
- Motor amperage draw
- Vibration signature
Changes in the baseline data should be noted, and decisions made as to maintenance required to effect maximum efficient operation of the pump. It should be kept in mind that bearings will inevitably fail. But failure is more often the result of the lubricating medium than the equipment itself. Careful attention to lubricants can save considerable time and effort by prolonging the life of the equipment.
Only non-foaming and non-detergent oils should be employed as lubricants for pumps. Oil should be kept at the level of the midpoint on the bull's-eye sight glass on the side of the bearing frame. Over-lubrication, one must remember, is as destructive as under-lubrication, because it will draw more horsepower, resulting in excess heat and possible frothing of the oil.
If any cloudiness is seen in the oil there is possibly water contamination, likely from condensation, of over 2,000 parts per million, indicating a need for an immediate oil change.
Where grease bearings are concerned, it is critical never to mix different consistencies or types of grease. Shields must be located toward the interior of the bearing frame. During re-greasing, the bearing fittings must be kept clean or the bearing life will decrease.
Like excess oil, over-greasing can lead to higher temperatures (localized in this case). This runs the risk of creating caked solids. However, after greasing temperatures may increase slightly for an hour or two.
Additional inspections should be undertaken whenever the terminal operator needs to replace a part. Signs to be looked for include excessive wear and cracks, or any indicators of fatigue. All parts should be replaced when the no longer meet tolerance standards:
- Bearing frame and foot should be inspected for cracking, rough spots, rust and scales. Machined parts should not have pitting or erosion.
- The bearing frame has tapped connections that should be examined for dirt. Threads should be cleaned and chased as needed, and foreign or loose material removed. Lubrication passages should be checked to make sure they are open.
- The shaft and sleeve should also be examined for grooves and pits. The bearing fits and shaft run out should be examined, and the shaft and sleeve replaced if worn or if run out is greater than 0.002 inches.
- There should be no wear, corrosion or pitting in the casing on visual inspection. Replace casing if wear exceeds 1/8 inch in depth. Gasket surfaces should be checked for irregularities or wear.
- If vanes on the impeller are worn more than 1/8 inch or bent at all, the impeller should be replaced.
- Look for cracks, warping, or corrosion in the frame adapter and replace if any damage is found.
- Look for visual signs of damage on the bearing housing, and replace if worn or out of tolerance.
- Look for cracks, pits, and signs of erosion in the seal chamber/stuffing box cover. Pay attention to war, scoring and grooves on the chamber face. Replace if there is any damage greater than 1/8 inch in depth.
- Inspect the shaft for signs of wear and damage, and also check the straightness. The maximum acceptable total indicator reading (TIR) at the sleeve journal and coupling joint should not be more than 0.002 inches.
Though requiring some work in terms of inspection, care and record keeping, this routine of maintenance and prevention can extend the equipment life of a pump and improve the safety of personnel and the environment in any fluid-handling operation.