Field Maintenance Guide for Rotary Gear Pumps: Repair Kits, Troubleshooting, and Preventive Care

What's Inside a NAPCO Repair Kit

NAPCO repair kits contain all wearing parts and elastomers necessary for a complete pump rebuild. The kit contents are engineered to restore pump performance to original factory specifications without replacing the housing or shaft (which rarely wear in normal service).

Standard Repair Kit Components

• Drive Gear Assembly: Factory-matched drive gear with internal shaft fitting, fully inspected and tested. This is the most critical component; no field modification or salvage is acceptable.
• Idler Gear Assembly: Factory-matched idler gear with bearing surfaces, ensuring precise gear mesh and long service life.
• Roller Bearings: High-load roller bearings for drive shaft and idler shaft. These support all radial and axial loads; wear results in clearance increases and vibration.
• High-Pressure Seals (Mechanical Seals): Primary fluid sealing surfaces that contain pressure inside the pump. Typically include rotating seal face, stationary seal face, and elastomer bellows.
• Low-Pressure Seals: Secondary seals at pump case suction ports and shaft extremities, preventing external leakage.
• Center Case Gaskets: Precision-molded elastomer gaskets that seal internal pump compartments. Gaskets are single-use and must be replaced during rebuild.
• O-Rings (Various Sizes): Assorted nitrile or Viton O-rings for port connections, drain plugs, and case sealing.
• Wear Plates: Precision-hardened plates that provide wear surfaces for gear teeth edges, extending gear life and reducing clearances.

What's NOT Included (And Why)

The housing, shaft, and end covers are not included in repair kits. These components are cast iron or stainless steel and rarely require replacement in normal service. They are inspected during rebuild but typically reused. If the housing is cracked, corroded, or damaged, contact NAPCO engineering for replacement housing availability.

Repair Kit Model Compatibility

NAPCO offers four standard repair kits matching the four primary pump configurations. Order the kit matching your installed pump model to ensure all components fit perfectly.

Critical: Do not attempt to mix repair kit components across pump models. PA300 and PA200 pumps use different gear displacements and bearing sizes. Using the wrong kit results in improper fit, mechanical failure, and potential safety hazards.

Preventive Maintenance Schedule

Regular preventive maintenance reduces unexpected failures and extends pump service life. The following schedule applies to normal-duty applications (continuous operation, moderate pressure, clean fluid). Applications with aggressive fluids, high pressure, or contamination may require more frequent inspection.

Weekly Inspection (Every 7 Days or 40 Operating Hours)

• Visual inspection for external leakage at pump case drain, shaft seal, and port connections
• Listen for unusual noise: grinding, squealing, or knocking indicates bearing or seal wear
• Check pump case temperature with infrared thermometer; normal operating temperature is 120-150°F
• Inspect inlet strainer for blockage; clean if flow is noticeably reduced

Monthly Inspection (Every 30 Days or 160 Operating Hours)

• Verify discharge pressure is within specified range; record readings for trend analysis
• Check flow rate (if possible) for degradation over time
• Inspect all hose connections and fittings for signs of seepage or weeping
• Test pump operation in bi-directional mode (if applicable); ensure smooth reverse operation

Quarterly Inspection (Every 90 Days or 500 Operating Hours)

• Comprehensive fluid analysis (if available): viscosity, water content, particle contamination
• Check seal for deterioration: any visible swelling, cracks, or separation indicates elastomer attack
• Bearing inspection for radial play: side-to-side movement at pump inlet flange should be minimal (<0.003")
• Gear wear evaluation: compare current flow rate to baseline; degradation >5% suggests wear
• Relief valve function test: verify system pressure response when flow is blocked

Annual Inspection (Every 365 Days or 2000 Operating Hours)

• Full pump disassembly and inspection (or complete repair kit replacement)
• Housing inspection for corrosion, pitting, or crack formation
• Shaft inspection for wear, scoring, or surface degradation
• Gear inspection for chipping, tooth wear, or fatigue cracks
• Complete seal replacement with factory repair kit
• Bearing replacement if play exceeds 0.005" or if any noise is detected

When to Rebuild: Warning Signs Your Pump Needs Service

Loss of Flow Rate (Primary Indicator)

Actual delivered flow is lower than rated specification and declining over time. Measure flow by timing how long it takes to fill a known volume. Compare to original equipment ratings. A 10% reduction suggests early gear wear; 20% or greater indicates rebuild is necessary.

Pressure Drop Without Corresponding Flow Increase

If system pressure drops below relief valve setting without increase in discharge flow, internal leakage (slip) is excessive. Worn gears no longer seal effectively; fluid leaks past gear teeth back to inlet side of pump. Rebuilding restores seal integrity.

Seal Leakage at Case Drain or Shaft

Visible fluid weeping from case drain port or shaft seals indicates seal failure or housing damage. Minor weeping (few drops per hour) may be tolerated; steady dripping or stream indicates immediate rebuild is necessary. Environmental contamination and fluid loss will accelerate.

Unusual Noise or Vibration

Grinding, squealing, or metallic knocking suggests bearing wear or gear damage. Grinding indicates metal-to-metal contact; this is a critical failure in progress. Stop the pump immediately and schedule rebuild. Continued operation risks housing damage and fluid contamination with metal particles.

Excessive Temperature Rise

Case temperature climbing above 170°F during normal operation indicates excessive friction from worn components or seal drag. High temperature accelerates elastomer degradation and reduces viscosity of the pumped fluid, compounding the problem. Rebuild will restore efficiency and temperature control.

Loss of Prime (Cavitation)

If the pump suddenly cannot draw fluid from the inlet or loses prime during operation, bearing wear may have increased internal clearances enough that the gear pump can no longer create sufficient inlet vacuum. Rebuild with new bearings restores sealing and priming capability.

High-Level Rebuild Procedure Overview

The following is a simplified overview of the pump rebuild process. Detailed technical manuals with step-by-step photographs and torque specifications are provided with each repair kit. This section is intended to familiarize maintenance teams with the general sequence.

Step 1: Isolation and Drainage

Isolate the pump from the system: close inlet and discharge isolation valves. Stop the motor. Allow the pump to cool to ambient temperature (5-10 minutes). Open the pump case drain plug and allow fluid to drain completely into a suitable waste container. Do not restart the pump during this process.

Step 2: Disassembly

Remove the six bolts connecting the center case to the end covers (three on inlet side, three on discharge side). Carefully separate the center case from the end covers using a soft mallet and block of wood; do not pry with metal tools. The drive and idler gears will remain in the center case during removal. Lift the center case assembly away and place on a clean work bench.

Step 3: Inspection

Inspect the housing interior for scoring, pitting, or corrosion. Minor surface oxidation is normal; deep pitting or cracks require replacement housing. Inspect gear teeth for chips, cracks, or unusual wear patterns. Inspect shaft for scoring or spalling. Take photographs for reference if damage is found.

Step 4: Gear and Bearing Removal

Remove the drive gear shaft from the center case by carefully extracting the shaft with bearings intact. Support the shaft weight; do not drop it. Remove the idler gear and its bearings using the same care. Inspect all bearings for radial play (rotation should be smooth with minimal side-to-side movement).

Step 5: Seal and Gasket Replacement

Remove the old high-pressure mechanical seals from the end covers. Remove the low-pressure seals and O-rings from the case. Clean all sealing surfaces with lint-free cloth and solvent. Install new gaskets, seals, and O-rings from the repair kit, using factory assembly drawings for correct orientation.

Step 6: Reassembly

Install the new gears and bearings from the repair kit, ensuring correct orientation and full seating. Install the center case back onto the end covers, aligning the bolt holes. Install the six connecting bolts and tighten to specified torque in a cross-pattern (top-bottom, left-right, alternating). Do not over-tighten; follow factory torque specifications exactly.

Step 7: Testing and Reinstallation

Before returning to service, fill the pump with clean fluid and rotate the shaft by hand to ensure free rotation (no grinding or binding). Verify all hoses and port connections are tight. Reinstall the pump in the system and refill with the original pumped fluid. Run at low speed for 5-10 minutes, monitor for leaks, and verify flow and pressure match baseline expectations.

Troubleshooting: Diagnosis and Solutions

Tools and Materials Required for Field Rebuild

Field rebuild of NAPCO pumps requires minimal specialty tools. Most facilities already have these items in their maintenance shops.

Essential Tools

• Metric socket set (8mm to 24mm) and wrenches
• Screwdrivers (Phillips and flat-blade)
• Soft mallet (rubber or plastic head, not steel)
• Wooden block and pry bar (for gentle disassembly)
• Torque wrench (0-100 ft-lbs range)
• Feeler gauges (for bearing clearance measurement)
• Caliper or micrometer (for dimension verification)

Materials and Supplies

• Clean, lint-free rags or paper towels
• Solvent for cleaning (mineral spirits or degreaser)
• Light machine oil or assembly lube (for reassembly)
• The appropriate repair kit (PK300S, PK300C, PK200S, or PK200C)
• Clean fluid matching the original pumped fluid (for testing)
• Waste container for old fluid disposal

Note: Factory repair kits include detailed assembly instructions, torque specifications, and dimensional drawings. Follow these exactly. Do not improvise or substitute components; mixed parts can result in improper fit and failure.

Field Serviceability Advantage in Remote Mining Operations

Remote mining sites (gold, diamond, explosives operations) often operate hundreds of kilometers from manufacturer support. A pump failure at a mine site cannot wait for a two-week shipment of replacement equipment. NAPCO's design philosophy recognizes this reality: every pump must be rebuil‌dable on-site with inventory of repair kits and basic hand tools.

Stock two repair kits for each pump model in your fleet. When a pump fails, your maintenance team rebuilds it on-site in 4-6 hours of labor. The failed pump is shipped to the authorized distributor for component refurbishment at your convenience. This approach maximizes production uptime and minimizes supply chain vulnerability.

Related Technical Resources

• How to Size a Rotary Gear Pump
• Gear Pumps for Corrosive Chemical Transfer
• Rotary Gear Pumps for Petroleum and Fuel Transfer
• Explosives & Mining Industry Solutions
• PK300S Repair Kit
• PK300C Repair Kit
• PK200S Repair Kit
• PK200C Repair Kit
• Engineering & Technical Support