4.9 Maintenance Programs, Asset Management & Pump Efficiency Testing

Maintenance Programs, Asset Management & Pump Efficiency Testing

The ABC Water Treatment Class IV outline devotes 20 items to Equipment Operation and Maintenance and names "perform corrective, preventative, and predictive maintenance," "conduct asset management," "complete equipment maintenance and repair records, including work orders," and "perform efficiency tests on pumps and related equipment (e.g., pump curves)" as separate tasks.

---

1. The Four Maintenance Strategies

The important insight is that preventive maintenance is not automatically better than run-to-failure. Over-maintaining is a real failure mode: infant mortality after intrusive work is well documented, and every disassembly introduces contamination and reassembly error. Match the strategy to the consequence of failure.

---

2. Condition Monitoring Techniques

Vibration analysis

The single most productive predictive technique on rotating equipment, because the fault frequency identifies the fault.

Other techniques

• Infrared thermography - electrical connections, motor control centers, bearings, steam and hot water systems, and building envelope. A loose lug shows up as a hot spot long before it fails.
• Oil analysis - viscosity, water, total acid number and total base number, and wear metals by spectrometry. Iron points at gears and shafts; copper at bushings and bearings; silicon at dirt ingress or, in an engine on digester gas, at siloxanes.
• Motor circuit analysis - insulation resistance (megger), polarization index, winding resistance balance between phases, and rotor influence checks.
• Ultrasonic - detects bearing lubrication distress before it becomes vibration, and finds compressed-air and steam leaks.
• Motor current signature analysis - detects broken rotor bars and load anomalies from the current waveform without instrumenting the driven machine.

Lubrication - the highest-value simple practice

More bearings die from lubrication error than from wear. The controllable errors are wrong lubricant, too much, too little, contaminated, and mixed incompatible greases. Practical rules: label every grease point with the specified lubricant, use color-coded dedicated grease guns, grease while the machine is running where safe so purged grease escapes, replace bearing housing breathers with desiccant breathers in wet environments, and store drums indoors, sealed, and horizontally on their side or under a cover.

---

3. The CMMS and Work Order Discipline

A computerized maintenance management system is only as good as the data entered in it. The minimum useful work order records:

• Asset identifier and location;
• Failure mode observed, coded consistently;
• Cause, where determinable;
• Action taken and parts consumed;
• Labor hours and downtime;
• Whether the failure was found by inspection or by breakdown.

That last field is the program's report card: a maturing program shifts work from breakdown-discovered to inspection-discovered. Useful program metrics include the ratio of planned to unplanned work (target 80 percent or higher planned), schedule compliance, PM completion rate, mean time between failures, and maintenance cost as a share of asset replacement value.

---

4. Asset Management

Asset management answers the question of which assets get the money. The framework a Virginia utility will encounter, and which the ABC criteria name directly, has five parts:

1. Asset inventory - what we own, where it is, what condition it is in.
2. Level of service - what performance the utility has committed to (pressure, reliability, water quality, response time).
3. Criticality - consequence of failure multiplied by likelihood of failure. A 40-year-old valve on a dead-end 4-inch main is old but not critical; a 12-year-old raw water pump with no redundancy is young and highly critical.
4. Life-cycle costing - the total cost to own, including energy, maintenance, and eventual replacement, not just purchase price. Energy usually dominates for pumps and blowers.
5. Long-term funding strategy - the renewal and replacement reserve, and the rate structure that funds it.

Remaining useful life is estimated from condition assessment and failure history, not from age alone. Two identical 1975 cast iron mains in different soils have very different remaining lives.

---

5. Pump Efficiency Testing

Pumps degrade quietly. Wear ring clearance opens, the impeller erodes, and the pump slides down and left on its curve while drawing nearly the same power. Field testing finds it.

The measurements required, simultaneously

1. Flow - a calibrated permanent meter, a portable ultrasonic meter, or a drawdown/fill test on a tank of known dimensions.
2. Suction pressure or lift at the pump suction gauge.
3. Discharge pressure at the pump discharge gauge.
4. Electrical input power - true kW with a three-phase power meter. Amps alone are not enough because power factor varies with load.
5. Elevations of both gauges and any velocity head difference between suction and discharge pipe sizes.

The arithmetic

TDH (ft) = (Discharge pressure - Suction pressure) x 2.31 + Gauge elevation difference + Velocity head difference

Water horsepower (WHP) = (Q x TDH) / 3,960, with Q in gpm

Input horsepower = kW x 1.341

Wire-to-water efficiency = WHP / Input horsepower

Pump efficiency = WHP / BHP, where BHP = Input hp x Motor efficiency

Worked example

A high-service pump delivers 1,150 gpm. Suction gauge reads 12 psi, discharge gauge reads 96 psi, both gauges at the same elevation with equal pipe sizes. The three-phase power meter reads 42.0 kW. Motor efficiency is 93 percent.

1. TDH = (96 - 12) x 2.31 = 194.0 ft
2. WHP = (1,150 x 194.0) / 3,960 = 56.3 hp
3. Input hp = 42.0 x 1.341 = 56.3 hp
4. Wire-to-water efficiency = 56.3 / 56.3 = 100 percent - which is impossible, and that is exactly how a field test tells you a measurement is wrong. Re-check the flow meter, the gauges, and the power meter before believing any efficiency above about 80 percent.

Corrected with a verified flow of 950 gpm:

1. WHP = (950 x 194.0) / 3,960 = 46.5 hp
2. Wire-to-water = 46.5 / 56.3 = 82.6 percent
3. BHP = 56.3 x 0.93 = 52.4 hp; pump efficiency = 46.5 / 52.4 = 88.8 percent - excellent, near the best efficiency point.

Interpreting the result

• Wire-to-water efficiency below about 60 percent on a clean-water pump means an investigation: worn wear rings, an eroded or plugged impeller, operation far off the best efficiency point, or a partly closed valve.
• Compare to the manufacturer's curve at the measured flow, not to a nameplate number. A pump that is 85 percent efficient at its BEP may be 55 percent efficient at 40 percent of BEP flow - and in that case the pump is not worn, it is simply the wrong pump for the duty, and the answer is a trimmed impeller or a variable frequency drive rather than an overhaul.
• Cost the loss. A 50 hp pump running continuously at 10 points below its achievable efficiency wastes roughly 50 x 0.746 x (10/85) x 8,760 hours, which is on the order of 38,000 kWh per year - an easy number to put in front of a utility director.

The cheapest energy project at most utilities is a pump test program, because it finds both worn pumps and mis-applied pumps, and because it produces defensible numbers rather than opinions.