Question: What makes a part reusable or not?
Asked by: Fire Pump Mechanics Worldwide.
Answer
When rebuilding a pump, deciding what to replace versus reuse is a common question. Fortunately, the process is straightforward: break the pump into individual components and evaluate each piece one at a time.
Always Replace These Items: Replace all the consumables and wear-prone parts, including: oil seals, O-rings, gaskets, rubber diaphragms, mechanical seals, nuts, bolts, screws, washers, snap rings, cotter pins, pipe plugs, rubber bellows, belts (V and synchronous), oil filters, thin shaft spacers (under 3.75-inches), microswitches, rubber flingers, drive yoke nuts, primer blades, shaft keys, and lubricants. These items are inexpensive and not worth assessing for reuse. If removed, replace them – especially lubricants and oil filters, which must always be refreshed.
Bearings and Clutches: Bearings should be replaced. Alongside mechanical seal failure, bearing wear is a leading cause of pump rebuilds. Diagnosing bearing damage like brinelling or raceway wear is difficult without specialized tools, so it’s best to replace them. If a clutch is removed, replace it. Evaluating torque fade is complex, and reusing a questionable clutch can compromise performance.
Rotary Screw Air Compressors: These should appear nearly pristine due to their oil-flooded operating conditions. If the screws show wear, don’t rotate freely, or exhibit rust beyond minor surface discoloration, replace the compressor. Also, flush all hydraulic lines and the oil reservoir feeding the compressor if it’s replaced.
Large Components: Clean and Inspect Major parts – casings, impellers, gearboxes, shafts, flanges, and housings – are sent to a vendor with an engine block cleaner. These industrial cleaners remove grime and odors, helping determine reuse viability. If the rotary screw compressor is reused, it doesn’t need this cleaning.
Visual and Functional Inspection: Replace parts with obvious defects: oblong shapes, destroyed bores, deep gouges, or signs of impact. Mounting surfaces must be smooth and undamaged to ensure proper alignment. Sealing surfaces for O-rings and gaskets must be continuous and free of scratches or dings. If sealing ability is in doubt, replace the part.
Use a fingernail to check for grooves on surfaces where oil seals contact shafts, yokes, or flanges. If a groove is felt, replace the part.
Assessing Rust and Wear: For pump casings and plumbing, ensure at least 90% of wall thickness remains. Reuse casings if cut-waters are intact and free of cracks or pitting. Impellers and seal rings should be measured against manufacturer specs. Impeller blades must be free of cracks and holes.
Shafts must be visibly straight, with spline teeth free of wear. Bearing mount surfaces should be continuous, and mechanical seal areas must be free of pits. Discolored parts post-cleaning often indicate overheating and should be discarded.
Gears and Clutch Components: Gears must have intact, crack-free teeth. Dog clutch teeth should be burr-free. Test mating clutch parts by hand – if they don’t slide together easily, replace them.
Threaded Holes and Final Advice: Part with stripped threads should be replaced. Heli-coil inserts are a last resort, used only when replacements are unavailable (e.g., vintage equipment).
When in Doubt: If you’re unsure about a part’s condition, replace it or contact us for guidance. This overview covers most scenarios and helps guide your decisions during a pump rebuild.
