When a newly repaired pump performs poorly, it seems logical that something is wrong with it. While that might be true, good troubleshooting procedures should also eliminate several other possibilities, including problems with the fluid being pumped (the pumpage), or with the pipes, fittings and vessels that are connected to the pump (the system). Fortunately, a savvy technician with just a basic understanding of pump curves and performance parameters can quickly narrow down the possibilities–especially those associated with the pump.

Pump curves

This discussion is limited to the most common pumps in industrial and commercial applications– centrifugal pumps. The performance curves in Figure 1 illustrate how the parameters of head, flow rate, efficiency and power relate to one another for a typical centrifugal pump. Note that as head increases, flow decreases, and vice versa (Head-Flow Pump Curve, Figure 1).

For any certain flow rate, there is a corresponding amount of head. The impeller design dictates a specific flow rate at which the pump will perform most efficiently–i.e., its Best Efficiency Point

(BEP). Many pump problems, and some system problems, will cause the pump to operate at a point below its normal pump curve line. A technician who understands this relationship can measure the pump parameters and isolate the problem to the pump, the pumpage, or the system.

Is it the pump?

To determine if the problem is the pump, the Total Dynamic Head (TDH) and flow should be measured at the pump and compared to the pump curve for that pump (see sidebar on page 49). The TDH is the difference between discharge and suction pressure, converted to feet or meters of head. (Caution: If there is little or no head or flow on start-up, the pump should immediately be shut off to verify that there is sufficient fluid in it–i.e., that the pump is primed. Running a pump dry may damage the seal.)

• If the operating point is on the pump curve, the pump is operating properly. Therefore, the problem is with the system or possibly the pumpage.

• If the operating point is below the pump curve, the problem could be the pump, the system, or possibly the pumpage.

Is it the pumpage?

Ambient conditions like temperature can change the viscosity of the pumpage, which in turn may change the head, flow and efficiency of the pump. Mineral-based oil is a good example of a liquid that changes viscosity with temperature. When the pumpage is a strong acid or base, dilution can change its specific gravity, which may affect the power curve.

To find out if the pumpage is the problem, its properties need to be verified. Tests for viscosity, specific gravity and temperature of the fluid are readily available and inexpensive. Standard conversion charts and formulas from the Hydraulics Institute and elsewhere can then be used to determine if the pumpage is adversely affecting the pump’s performance.

Is it the system?

Assuming the fluid properties have been ruled out, the problem must be with the pump or the system. Again, if the pump is operating on the pump curve, it is working properly. In that case, the problem must be the system to which the pump is connected.

There are two possibilities here. Either the flow is too low (and therefore the head is too high), or the head is too low (indicating the flow is too high). When considering head and flow, remember that the pump is operating on its curve. Therefore, if one is too low, the other must be too high.

Low flow (head too high). A low flow condition usually indicates a restricted line. If the restriction is in the suction line, there will likely be cavitation; otherwise, it is probably in the discharge line.

Other possibilities are that the suction static head is too low, or that the discharge static head is too high. For example, a suction tank may have a float switch that fails to shut off the pump when the fluid level drops below the set point. Similarly, a discharge tank may have a “high level” switch that has malfunctioned. a discharge tank may have a “high level” switch that has malfunctioned.

Low head (flow too high). A low head condition indicates too much flow. And it is likely that the flow is not going where it should. System leaks can be internal or external. A diverter valve that allows too much flow to bypass, or a failed check valve that lets flow circulate backwards through a parallel pump, would result in too much flow and low head. On a municipal water system with buried water mains, a major leak or line break will allow too much flow and result in low head (low line pressure).

Blockages and leaks. Looking for blockage or leaks in a hydraulic system is like looking for opens and shorts in an electrical system, except that the parameters to measure are pressure and flow rather than voltage and current. Where there is a blockage or a leak, there will be an abnormal pressure differential across the area or component involved. It is easier to locate a problem by checking pressure (THD) than by measuring flow (see sidebar).

Other system problems. Even if the pump is not operating on its curve, there are some system problems that must be ruled out before the pump can be identified as the culprit. For example, if vapor is getting into the pump by air entrainment or cavitation, the pump will not operate on its curve, even if there is nothing wrong with it. Performing vibration analysis in real time while varying the pump suction will help identify cavitation and air entrainment. If the pump does not operate on its curve after these conditions have been eliminated, there is very likely a problem with the pump.

What could be wrong with the pump?

When a pump does not operate on its curve and cavitation and air entrainment have been eliminated, the most likely causes are a damaged impeller, blockage in the impeller (see Figure 3), blockage in the volute, or excessive wear ring or impeller clearance. Other causes would be related to the speed of the pump, such as the shaft spinning in the impeller, or an incorrect drive speed. While drive speed can be verified externally, investigating the other causes will involve opening the pump.

Conclusion

Troubleshooting pump performance is straight-forward. By measuring the pump’s head and flow and comparing the results to the manufacturer’s pump curve, and checking for air entrainment and cavitation, the technician can readily determine if the problem is with the pump or the system. The properties of the pumpage can also be tested to rule them out as the cause of the problem.

EASA is an international trade association of more than 1,700 firms in nearly 70 countries that sell and service electromechanical apparatus. For more information, visit www.easa.com .

Text: Gene Vogel, pump and vibration specialist at EASA
Images: EASA and SHUTTERSTOCK

Casing distortion is not only one of the biggest problems for rotating machinery, but is also a very common one. But what does it actually mean? To explain it, we can use the famous analogy of a rocking table in the restaurant. This is a situation everybody can relate to. Due to an uneven floor or bad construction of the table, there is space under one leg which makes the whole table rock from one side to another. It is a problem that is easy to solve, just use a few napkins and the table will stay still.

The same happens when placing rotating machinery on a foundation that is not flat. Most rotating equipment is designed to be installed on a flat surface. At the manufacturer site, all machine feet are milled to be in a perfectly flat plane. When placing the equipment on a non-flat foundation or uneven sole plates, it will reproduce that rocking situation we just mentioned. That is what we call “soft foot”.

Tiny clearances, big impact

Rotating equipment consists of many parts: rotors, shafts, bearings, mechanical seals, impellers in compression chambers, just to mention a few. And these all have very small internal clearances. If a machine is bolted down on an uneven surface, the forces applied on the machine feet will change the casing geometry. As a result, these clearances will quickly change.
To fix a soft foot condition, is necessary to compensate everything above 0.05 mm. That is not much, if you consider the fact that the thickness of a human hair is between 0.06 mm to 0.08 mm! This is how little it takes to convert our new or newly overhauled machine into a victim of casing distortion.

Pipe connection issues

Another possible cause for casing distortion is pipe strain. Pipe strain can occur when the pipes are wrongly fabricated, and the connection flanges are not aligned. It can also be that the pipe supports are too high or too low, which creates large gaps between the connections. A common solution for this is to force them together, which will result in what we call nozzle load. This too will put a lot of stress on the machine casing. (The OEM will specify the allowed nozzle load on the equipment.)

The long-term consequences

So what kinds of problems can you run into if casing distortion occurs? Previously we mentioned the internal parts of rotating machinery, such as shafts. How do they get affected?

Well, shafts have mounted bearings to carry the rotating motion, and these bearings operate under designed loads. When casing distortion occurs, the shafts are put under strain and their positions change. That will affect the bearings by changing their designed load, and the rolling elements inside the bearing will move from designated race way. This is something that will seriously affect lubrication. The rolling elements of the bearing will push away the lubrication since there will be no space for it.

Heat will build up and produce more thermal expansion of internal components, which will gradually reduce their gap until, inevitably, failure occurs. (Changing the designed loads in the bearings will reduce bearing life by as much as 50%.)

Ensuring proper installation can make the difference between smooth operation and unexpected failure. As we have seen, all it takes is a minor gap to throw your machinery off balance. When it comes to rotating equipment, precision is a necessity.

Text: Roman Megela, Senior Reliability Engineer, Easy-Laser AB
Images: Easy-Laser AB

What is Preventative Maintenance in Construction?

In the intricate tapestry of the construction industry, preventative maintenance stands out as a pivotal practice, underpinning the operational longevity and efficiency of critical machinery. It encompasses a systematic regimen of inspection, detection, rectification, and proactive measures to stave off potential equipment failures before they burgeon into tangible issues. This methodology transcends the rudimentary act of merely repairing a malfunctioning machine; it delves into a rigorous, routine-based examination and servicing paradigm, ensuring machinery remains in pristine working condition, thereby preventing unforeseen breakdowns.

Take, for example, a towering crane, an indispensable asset in a construction site’s arsenal. Rather than adopting a reactive stance and awaiting an inevitable malfunction, preventative maintenance adopts a proactive approach. This involves meticulous scrutiny of its intricate components, including cables, pulleys, and hydraulic systems.

Activities such as lubrication, calibration of loose parts, replacement of components exhibiting wear and tear, and periodic software updates (if the machinery is digitally integrated) are integral to this regimen. According to a study by the Construction Equipment Management Program, regular preventative maintenance can enhance equipment life by up to 60%. Such a methodical and sophisticated approach not only ensures that the crane operates at its zenith of capacity but also significantly diminishes the probability of unanticipated operational downtimes, which can have cascading repercussions on project timelines and costs.

The Benefits of Using Preventative Maintenance in Construction

Significant Cost Savings in Many Areas of The Business In the intricate world of construction, where financial margins are often razor-thin, the role of preventative maintenance stands out as a beacon of fiscal responsibility. At first glance, the outlay for regular equipment upkeep might appear as an added expenditure. However, delving deeper into the financial matrix reveals a different narrative.

Unplanned equipment breakdowns, often resulting from neglect, can lead to exorbitant repair costs. According to the National Research Council, the financial implications of such reactive maintenance can be up to nine times more than a well-planned preventative approach. Beyond the direct repair expenses, the ripple effects of these breakdowns, such as project delays and potential contractual penalties, further strain project budgets.

Moreover, the longevity of machinery is intrinsically tied to its maintenance regimen. By investing in preventative care, construction firms can significantly defer the hefty capital outlays associated with equipment replacement. Research from the Construction Industry Institute underscores this, suggesting that machinery under a preventative maintenance umbrella can see its operational life extended by 20-40%. This elongation represents not just a delay in replacement costs but also ensures that the equipment operates at peak efficiency, leading to reduced operational costs.

In summation, the financial wisdom of preventative maintenance in the construction sector is evident. While there’s an upfront cost, the long-term savings, both direct and indirect, make it an indispensable strategy for firms aiming for fiscal prudence and project success.

The Role of Preventative Maintenance in Ensuring Equipment Longevity in Construction In the construction realm, equipment longevity is not just a financial asset but a cornerstone for seamless operations and sustained business growth. At the heart of this longevity lies preventative maintenance—a proactive approach that ensures machinery not only endures but operates at its zenith, bringing manifold strategic benefits to construction entities.

Central to these benefits is the consistent operational efficiency that well-maintained equipment guarantees. The Construction Industry Institute underscores this, highlighting that machinery under a rigorous preventative maintenance regimen retains a vast majority of its operational prowess throughout its lifecycle. This directly translates to projects adhering to their timelines, fortifying a company’s reputation for reliability and punctuality.

Additionally, the stability offered by equipment longevity, courtesy of preventative maintenance, means that operators gain in-depth familiarity with their machinery. This continuity ensures that operators master their equipment, leading to optimized performance and minimizing errors—a crucial edge in an industry where precision is non-negotiable.

Lastly, preventative maintenance not only ensures the equipment’s operational longevity but also preserves its intrinsic value. When the juncture arises to upgrade or divest, equipment that has been consistently maintained through preventative measures commands a premium in the secondary market, testifying to the enduring value of preventative care in the construction sector.

Enhanced Safety as a Result of Well-Maintained Assets In the construction sector, where the interplay of machinery and manpower is constant, safety remains paramount. Preventative maintenance emerges as a critical strategy to address the inherent risks, ensuring that equipment functions optimally and safely, thereby safeguarding the workforce.

The Occupational Safety and Health Administration (OSHA) has highlighted equipment-related incidents as a significant contributor to on-site injuries. However, the proactive approach of preventative maintenance can mitigate these risks. A study by the National Safety Council underscores this, revealing that up to 70% of machinery-related accidents could be averted through timely inspections and consistent maintenance. This proactive approach ensures that potential equipment malfunctions are identified and rectified before they escalate into safety hazards.

Moreover, the Bureau of Labour Statistics notes that the construction domain experiences a higher rate of fatal work injuries than many other sectors. Equipment malfunctions, unfortunately, play a pivotal role in these statistics. By integrating preventative maintenance into their operational protocols, construction firms can substantially diminish these incidents. This not only protects the workforce but also reinforces the company’s commitment to safety.

By proactively ensuring the health and efficiency of equipment, construction companies can create a safer environment for their employees, reduce potential liabilities, and deliver projects that stand as testaments to both quality and safety.

Environmental Benefits

The construction industry, with its heavy reliance on machinery and equipment, has a significant environmental footprint.

However, preventative maintenance emerges as a potent tool in mitigating these environmental impacts, offering benefits that extend beyond mere operational efficiency.

• Reduced Fuel Consumption: Machinery that undergoes regular preventative maintenance operates at its peak efficiency. According to the U.S. Department of Energy, well-maintained equipment can reduce fuel consumption by up to 10-15%. This not only translates to cost savings but also means fewer fossil fuels are burned, leading to a reduction in greenhouse gas emissions.
• Decreased Emissions: Emissions from construction equipment, particularly older models, can be a significant source of air pollution. The Environmental Protection Agency (EPA) notes that preventative maintenance, including timely oil changes, filter replacements, and engine tune-ups, can reduce emissions by up to 40%. This plays a crucial role in improving air quality, especially in urban areas where construction activities are frequent.
• Waste Reduction: Preventative maintenance also means fewer parts replacements and less waste. A study by the Construction Industry Research Board found that regular equipment checks can reduce waste from worn-out parts by up to 50%. This not only conserves resources but also reduces the burden on landfills.
• Resource Conservation: Efficient machinery requires fewer resources, from lubricants to replacement parts. The International Journal of Construction Management highlights that preventative maintenance can lead to a 20% reduction in the use of ancillary materials, further diminishing the industry’s environmental impact.
• Noise Pollution: Well-maintained equipment tends to operate more quietly, reducing noise pollution—a significant concern in urban construction sites. The World Health Organization has identified noise pollution as a major environmental health risk, and by ensuring equipment operates smoothly through preventative maintenance, construction companies can contribute to quieter, more liveable urban environments.

Preventative Maintenance as Part of a Comprehensive Maintenance Strategy

While preventative maintenance offers numerous benefits, it should not be viewed in isolation. Instead, it should be a part of a comprehensive maintenance strategy that also includes corrective maintenance (fixing things when they break down) and predictive maintenance (using data analytics to predict when a machine might break down). By integrating preventative maintenance into a broader strategy, construction companies can ensure that their equipment is always in the best possible condition, leading to efficient operations and successful project completions.

In Conclusion

The integration of preventative maintenance into a holistic maintenance strategy, encompassing both corrective and predictive maintenance, is emblematic of a forward-thinking, responsible, and sustainable approach to construction. Such a comprehensive strategy not only ensures the optimal performance of equipment but also safeguards the well-being of workers, the environment, and the broader community.

In the ever evolving and competitive arena of construction, companies that prioritize and invest in preventative maintenance position themselves at the forefront, setting industry standards and paving the way for a safer, more efficient, and environmentally conscious future. In essence, preventative maintenance is not merely an operational choice but a defining pillar for construction entities aspiring for excellence, sustainability, and enduring success.

Text: Charlie Green, Senior Research Analyst at Comparesoft Images: stockphoto

Good, readily available records are essential for any motor storage program. One method is to attach a form like that in Figure 1 to each motor to document the storage dates, maintenance procedures completed, and the results of all tests performed during the storage period.

For motors in long-term storage, a good practice is to replace the form annually (or at other designated intervals). Store electronic copies of the previous forms for future reference, or simply keep them in an envelope attached to the motor.

Storage conditions

Short-term storage. Motors that will be in storage for just a few weeks primarily require protection from the weather (see “Indoor storage” and “Outdoor storage” below) and ambient vibration (more on this later).

Long-term storage. Motors slated for several weeks to several years in storage and all above-NEMA size machines require additional preparations to protect their machined surfaces, bearings and windings.

Indoor storage. If possible, store motors indoors in a clean, dry area. Place horizontal machines in a horizontal position and vertical motors in a stable vertical position.

Unless the storage area is climate controlled, prevent condensation from forming inside the motor by energizing the space heaters (if supplied) to keep the windings 5-10°C (10-20°F) above the ambient temperature. (For other ways to prevent condensation, see “Special care for windings” below.)

Outdoor storage. Don’t! Seriously, if a motor is too large to store indoors, it is likely to be a very expensive machine. It’s worth the cost to construct an enclosed storage facility. When outdoor storage is absolutely necessary, protect the motor with a waterproof cover (e.g., a tarp), allowing a breathing space at the bottom. Wrapping it tightly in plastic and placing it outdoors will cause condensation to form inside the motor due to the temperature extremes and humidity.

Outdoor storage also requires preventive measures to keep out rodents, snakes, birds or other small animals that can damage the winding insulation. If insects are prevalent, keep them from blocking ventilation and drain openings by loosely wrapping the motor and covering all openings.

Shafts and machined surfaces

Apply a viscous rust/corrosion inhibitor (e.g., LPS2, Techtyl 502C or RustVeto) to exposed machined surfaces and sleeve bearings, allowing it to remain intact throughout the storage period. In humid and rainy/snowy environments, have the service center paint as much of the motor’s interior surface as practical, and coat the windings with a topical fungicide in tropical environments. (Note: Disassemble the machine and inspect the sleeve bearings before placing it into service.)

Bearing protection

Grease-lubricated motors. For long-term storage, completely fill the bearing cavities with compatible grease to prevent rust and corrosion staining that can occur if moisture collects between the balls and races.

Oil-lubricated motors. Do not ship or move these motors with oil in the reservoir. After placing the motor in storage, fill the reservoir with enough oil to cover the bearings but without overflowing the stand tube or labyrinth seal. Fill sleeve bearing machines to just below the labyrinth seal and vertical motors to the “max fill” line.

The oil should contain a rust and corrosion inhibitor and be moisture free. Check it every three months by drawing a sample from the drain. Since water weighs more than oil, any moisture will be evident.

Ambient vibration. This can damage motors, even when they are not rotating. Proximity to rail lines, busy roads, and/or production floors can all contribute to the ambient vibration. Even low-magnitude vibration, over time, can damage bearings while they are stationary–e.g., false brinelling (see Figure 2). Solutions vary. For example, one mill that had ambient vibration from nearby machinery stored its motors on scrapped conveyor belting.

False brinelling damages the bearing race at uniform intervals matching the spacing of the rolling elements. Although the damage initially may appear slight or even invisible to the naked eye, it often progresses rapidly once the motor is in service.

Shaft rotation. Turning the motor’s shaft at least monthly during long-term storage redistributes lubricant on machined surfaces to inhibit corrosion. Motors with ball or roller bearings also benefit from monthly rotation, since the rolling elements stop in different positions each time. Larger, 2-pole machines require more frequent attention than smaller (NEMA-frame) machines.

Motors with spring-loaded spherical bearings are more difficult to turn, but they still require manual rotation to coat the bearings with oil. With sliding plate (i.e., Kingsbury) bearings, lift the shaft before rotating it–from below with a short jack and a bearing ball centered on the shaft, or from above with an overhead crane and eyebolts. To avoid bearing damage, be careful not to lift the shaft more than a few mils.

Machines with heavy rotors and long frames in ratings of about 2000 hp (1500 kW) and larger sometimes require more frequent (weekly) rotation to prevent shaft bowing caused by the weight of the rotor. As an extreme example, power plants often keep large turbine generators rotating slowly all the time to prevent sag. While it is uncommon, removing and vertically suspending the rotors of very large critical machines also can prevent sagging.

Special care for motor windings

Methods for preventing condensation. Motor windings must stay clean and dry to keep the insulation from degrading. Unless the storage area is climate controlled, condensation can form in the motor if the temperature of the winding dips below the dew point. As mentioned earlier, the usual way of avoiding this is to keep the winding 5-10°C (10-20°F) above ambient temperature.
If the motor has space heaters, energize them while it is in storage; if not, add them. Another option is to use the windings as a resistance heater by supplying low-voltage DC current (approximately 8-12% of rated amperage). An energy-saving alternative is to lower the dewpoint of the storage room with a dehumidifier.

Insulation resistance (IR) tests. Measure and record the IR of the winding(s) before storing a motor even a few weeks, and again just before putting it in service (see Figure 3). Correct all IR readings to a standard temperature and address any decrease in IR before installing the motor. If a motor will be in storage for a long time, take IR readings annually.

Polarization index (PI) and dielectric absorption ratio (DAR) tests. For form coil windings, conduct a PI test in addition to the IR test. The PI test variables skew results for windings with lots of exposed conductor surface area, so use the DA ratio test for random windings and DC armatures (see Tables 1 and 2).

If the windings need to be cleaned and dried, measure the IR again. If it is greater than 5000 megohms, disregard the PI (see IEEE 43); otherwise, recalculate the PI.

Insulation resistance (IR) tests. Measure and record the IR of the winding(s) before storing a motor even a few weeks, and again just before putting it in service (see Figure 3). Correct all IR readings to a standard temperature and address any decrease in IR before installing the motor. If a motor will be in storage for a long time, take IR readings annually.

Polarization index (PI) and dielectric absorption ratio (DAR) tests. For form coil windings, conduct a PI test in addition to the IR test. The PI test variables skew results for windings with lots of exposed conductor surface area, so use the DA ratio test for random windings and DC armatures (see Tables 1 and 2).

If the windings need to be cleaned and dried, measure the IR again. If it is greater than 5000 megohms, disregard the PI (see IEEE 43); otherwise, recalculate the PI.

Carbon brushes

DC machines, wound-rotor motors and some synchronous machines have carbon brushes. For long-term storage, lift the brushes away from the commutator/slip rings to prevent a chemical reaction (sometimes called “photographing”) that can discolor the underlying commutator or slip ring. When practical, store the springs in the relaxed state to prevent a gradual loss of spring pressure.

Putting the motor into service

To ensure proper operation when removing a motor from storage and putting it into service, perform the following:

• Use compressed air to clean the outside of the motor, and visually inspect it.
• Assess the condition of the insulation system by measuring the IR with a megohmmeter.
• Oil-lubricated motors:
• Drain the oil before moving the motor to the installation site.
• If there is water in the oil, check for and replace any rusty bearings.
• If sleeve bearings received a protective coating, disassemble the machine and clean the bearings with an appropriate solvent before putting the motor into service.
• Fill the oil reservoir to the correct running level after installing the motor.
• Grease-lubricated motors:
• Moisture in the grease usually indicates rust-damaged bearings that need replacement.
• After several years in storage, the grease probably will be hard and the drainpipe will be plugged; usually it is best to disassemble the motor, remove the old grease and repack with fresh, compatible lubricant.
• Run the motor 10-20 minutes without the drain plug to purge excess grease.
• Vibration and alignment:
• If the storage area has ambient vibration, inspect and replace damaged bearings before installing the motor.
• After installing and aligning the motor, document the uncoupled baseline vibration levels; check the levels again after a week or two of service.
• For motors with rolling element bearings, check for bearing fault frequencies in the vibration spectra.
• On large machines that are susceptible to shaft sag, monitor the vibration levels during startup to avoid catastrophic damage.

High-cost machines obviously justify more precautions than inexpensive, readily available motors. What is not always apparent is that some “smaller” motors are equally important to production and can have enormous consequences if they fail.

References
IEEE Std. 43-2013: Recommended Practice for Testing Insulation Resistance of Electric Machinery. Institute of Electrical and Electronics Engineers, Inc. New York, NY, 2013.

Text: Chuck Yung, senior technical support specialist at EASA, Inc., St. Louis, MO USA     Images: EASA, stockphoto