Why Scheduled Maintenance Matters
Preventive maintenance is the foundation of reliable pump operation. A structured maintenance program prevents unplanned downtime, extends pump service life, maintains consistent performance, and reduces total cost of ownership. Rotary gear pumps are robust and long-lived when properly maintained — the key is catching wear early before it cascades into component failure.
This guide provides a comprehensive maintenance schedule organized by interval: daily checks, weekly inspections, monthly verification, quarterly analysis, and annual overhaul. Following this timeline ensures your pump delivers rated flow and pressure while maximizing time between rebuilds.
Daily Checks (Every Shift or Daily)
Perform these quick inspections at the start of each shift or daily operation to catch early warning signs.
Visual Leak Inspection
Inspect the entire pump housing, case drain port, shaft seal area, and all fittings for visible leakage. A few drops per hour at the case drain is normal; steady dripping or streaming indicates seal degradation. Look for wet spots on the floor beneath the pump. Minor weeping at port connections may tighten with hand pressure; significant leaks require immediate attention.
Listen for Unusual Noise
Run your hand near (but not touching) the pump housing to feel for vibration. Listen carefully for cavitation (high-pitched whine), bearing wear (grinding), or gear contact noise (metallic knocking). Unusual noise that changes with speed or load may indicate bearing wear or seal drag. Normal operation should be a smooth, low-frequency hum.
Check Inlet and Outlet Pressure Gauges
Verify that discharge pressure is within specification and remains steady during constant-speed operation. Inlet gauge should show slight vacuum (negative pressure) during normal suction. If inlet pressure drops significantly, check for air leaks at the suction line or clogged strainer.
Monitor Motor Amperage
If the pump is motor-driven, note the current amperage draw. Rising amperage at constant speed indicates increased internal friction from worn components or seal drag. A 10–15% increase suggests early wear; 20% or greater increase warrants immediate inspection. Compare today’s reading to baseline readings recorded during normal operation.
Verify Consistent Flow Rate
If possible, verify that discharge flow appears consistent and does not fluctuate. Pulsating flow or sudden drops may indicate cavitation, bearing wear, or inlet starvation. Flow should be steady regardless of minor pressure variations.
Weekly Maintenance (Every 7 Days or ~40 Operating Hours)
Inspect and Clean Suction Strainer
Check the inlet strainer for blockage or contamination. A clogged strainer reduces inlet pressure and forces the pump to cavitate. If the suction gauge shows vacuum greater than 3–5 inches of mercury, clean the strainer immediately. Replace the strainer cartridge if cleaning does not restore flow.
Check for Vibration
Use a vibration meter or your hand to detect excessive vibration at the pump case. Slight vibration is normal; noticeable hand-feel vibration may indicate bearing wear, cavitation, or coupling misalignment. Compare to baseline vibration recorded during commissioning.
Verify Relief Valve Operation
Block the pump discharge (close outlet valve) and observe pressure rise on the discharge gauge. When pressure reaches relief valve setting, the pump should unload smoothly without sudden pressure spikes or chattering. Relief valve failure can allow runaway pressure that damages seals and hoses.
Inspect Coupling Alignment
Check motor-to-pump coupling for visible runout or misalignment. A misaligned coupling increases bearing loads and vibration. If coupling bolts are loose, tighten and verify alignment with a feeler gauge.
Check Mounting Bolt Torque
Verify that all pump mounting bolts are tight. Loose mounting causes vibration and noise. Use a torque wrench to re-tighten to factory specification if needed.
Monthly Maintenance (Every 30 Days or ~160 Operating Hours)
Lubricate Bearings
NAPCO pumps use sealed roller bearings that are pre-lubricated at the factory. Most installations require no additional lubrication. If your pump has grease fittings or oil lubrication points, follow the original equipment manual for frequency and lubricant type. Over-lubrication can cause seal failure.
Inspect Shaft Seal for Weeping
Examine the shaft seal area where the pump connects to the motor coupling. A few drops of fluid at the seal is normal; continuous weeping (more than a few drops per hour) indicates seal degradation. Consistent weeping will lead to fluid loss and eventual seal failure; plan rebuild in the next 1–2 months if weeping increases.
Check Gasket Integrity
Inspect all visible gasket seals for signs of leakage, cracks, or separation. Case drain gaskets and port seals may weep if degraded by fluid chemistry or high temperature. Minor leakage may be tolerated; significant leaking warrants near-term rebuild planning.
Record Performance Data for Trend Analysis
Document discharge pressure (PSI), measured or estimated flow (GPM), motor amperage (amps), and case temperature. Maintaining a trend log over months allows you to detect gradual wear. A 5–10% monthly decline in flow suggests early gear wear; 20% decline warrants quarterly rebuild consideration.
Clean Exterior of Pump Housing
Remove dirt, dust, and debris from the pump case. Caked-on dust can trap heat and reduce cooling; clean surfaces help maintain optimal operating temperature. Use a soft brush or compressed air; do not use high-pressure washers that may force water into seals.
Quarterly / Semi-Annual Maintenance (Every 90 Days or ~500 Operating Hours)
Measure Bearing Play
Use a feeler gauge to measure radial side-to-side movement at the pump inlet flange. Grasp the gear assembly and gently rock it back and forth. Bearing clearance should be minimal: less than 0.003" (75 microns) is ideal. If play exceeds 0.005", bearings are near replacement threshold. This is the most reliable indicator of internal wear without full disassembly.
Measure Gear Tooth Profile for Wear
If your facility has precision calipers or micrometers, measure gear tooth height and compare to factory specifications. Advanced wear is difficult to detect without specialty tooling; this step is optional unless wear is suspected.
Inspect Bearing Condition
Rotate the pump shaft by hand and listen for grinding, roughness, or noise inside the bearing. Normal bearings should rotate smoothly with minimal friction. Any grinding or resistance indicates bearing wear; plan rebuild within 1–2 months.
Pressure Test the Relief Valve
Close the discharge outlet and slowly increase pump speed while monitoring pressure. The relief valve should open at the specified setting (±5% tolerance). If it opens too early or too late, adjust or replace the valve cartridge. A malfunctioning relief valve risks overpressure damage to hoses and seals.
Check All Piping Connections for Tightness
Inspect inlet, discharge, and case drain hoses and fittings. Tighten any loose connections with a wrench. Check hose condition for cracks, splits, or brittleness. Replace hoses that show signs of age or degradation.
Annual Overhaul / Rebuild (Every 365 Days or ~2000 Operating Hours)
Once per year, perform a complete disassembly and inspection or replace all wearing parts using a factory repair kit. This interval assumes normal-duty continuous operation in a clean environment. Aggressive applications (high pressure, elevated temperature, contaminated fluid) may require semi-annual overhaul.
Full Disassembly and Inspection
- Remove center case from end covers; inspect housing bore for scoring, pitting, or wear
- Inspect drive and idler gears for tooth wear, chipping, or micro-spalling
- Inspect shaft for scoring, spalling, or surface degradation
- Inspect all bearings for wear, noise, or play exceeding 0.005"
- Document findings with photographs if damage is present
Replace All Elastomers and Wearing Parts
- Replace high-pressure mechanical seals with factory components
- Replace low-pressure seals and all O-rings
- Replace center case gaskets (single-use; do not reuse)
- Replace roller bearings if play exceeds 0.003" or if any noise is detected
- Replace wear plates if scored or worn
Verify Housing and Shaft Condition
Inspect the housing bore for cracks or major pitting. Minor oxidation is acceptable; deep pitting or cracks require housing replacement. Measure shaft runout with a dial indicator; runout greater than 0.003" indicates shaft damage requiring replacement.
Reassemble, Prime, and Test
Reassemble using factory torque specifications and assembly drawings. Fill the pump with clean fluid and hand-rotate the shaft to ensure free movement. Verify all connections are tight. Reinstall in the system and run at low speed for 5–10 minutes. Monitor for leaks and verify flow and pressure match original equipment specifications.
Maintenance Frequency Reference Table
Use this quick-reference table to organize your maintenance schedule.
| Frequency | Task | Effort |
|---|---|---|
| Daily | Visual leak inspection, listen for noise, check pressure gauges, monitor amperage, verify flow | 5–10 min |
| Weekly | Clean inlet strainer, check vibration, test relief valve, inspect coupling, tighten mounting bolts | 15–30 min |
| Monthly | Lubricate bearings (if required), inspect seal for weeping, check gaskets, record pressure/flow/amps/temp, clean housing | 30–45 min |
| Quarterly | Measure bearing play, measure gear wear, inspect bearing condition, pressure test relief valve, tighten connections | 45–90 min |
| Annual | Full disassembly or complete repair kit replacement, replace all elastomers, bearings, seals, gaskets, reassemble and test | 4–8 hours |
Signs It's Time to Rebuild Your Pump
Do not wait for the annual interval if warning signs appear. Rebuild immediately if you observe any of the following.
Reduced Flow at Same RPM (Primary Indicator)
A 10–20% reduction in flow suggests early gear wear. A 20%+ reduction indicates rebuild is necessary. Measure flow by timing how long it takes to fill a known volume at constant pump speed.
Increasing Motor Amperage
Rising amperage at constant speed indicates increased internal friction. A 10–15% increase above baseline suggests early wear requiring quarterly inspection; 20%+ increase warrants immediate rebuild planning.
Visible or Audible Seal Leakage
Weeping at case drain or shaft seal that increases over time is an early warning. Streaming (continuous flow) indicates immediate rebuild is needed. Environmental contamination and fluid loss will accelerate if operation continues.
Unusual Grinding, Squealing, or Knocking Noise
Grinding indicates bearing wear or gear damage. Squealing suggests cavitation or bearing distress. Metallic knocking indicates gear contact or bearing failure. Any of these sounds warrants immediate pump shutdown and rebuild planning. Continued operation risks housing damage and fluid contamination with metal particles.
Excessive Temperature Rise
Case temperature above 170°F during normal operation indicates excessive friction from worn components or seal drag. High temperature accelerates elastomer degradation and reduces fluid viscosity, compounding the problem.
Loss of Prime or Cavitation
If the pump cannot draw fluid from the inlet or loses prime during operation, bearing wear may have increased internal clearances enough that the pump can no longer create sufficient inlet vacuum. Rebuild with new bearings restores sealing and priming capability.
Bearing Play Exceeding 0.005"
Measured radial clearance greater than 0.005" at the pump inlet flange indicates bearing wear beyond acceptable limits. Rebuild immediately to restore tight tolerances and pump performance.
Maintenance Checklist
A printable maintenance checklist is available to help you track inspections and maintain detailed records of your pump’s condition over time. Contact NAPCO engineering for a customized checklist tailored to your specific pump model and application.
Contact our technical team to request a printable maintenance checklist and schedule customized training for your maintenance staff.
Repair Kit and Material Reference
When it’s time to rebuild, use these factory-matched repair kits and material specifications.
NAPCO Repair Kits
- PK300S — Stainless steel housing, 26.5 cc/rev
- PK300C — Ductile iron housing, 26.5 cc/rev
- PK200S — Stainless steel housing, 11.5 cc/rev
- PK200C — Ductile iron housing, 11.5 cc/rev
Bearing and Seal Materials
- Bearings: Chrome needle roller bearings rated for high-load industrial service
- Gear Material: Nitrile (standard, rated to 240°F) or Viton (high temp/chemical resistance, rated to 350°F)
- Seals: Viton high-pressure and low-pressure seals for chemical resistance and temperature stability
- Gaskets: Asbestos-free precision-molded paper; single-use only
Related Technical Resources
Need Maintenance Guidance or Repair Support?
NAPCO’s engineering team is ready to help you develop a maintenance schedule tailored to your specific application, answer questions about rebuild timing, and provide technical guidance on component selection and inspection procedures.