Common Failure Modes
Common Positive Displacement Pump Failures
Positive displacement pumps fail in predictable ways when internal clearances, seal integrity, or rotor geometry degrade. Understanding these failure modes helps identify early warning signs and prevents catastrophic breakdowns.
01
Internal Leakage and Volumetric Efficiency Loss
As rotor lobes, piston bores, or plunger surfaces wear, internal clearances increase beyond design tolerance. Fluid bypasses the pumping chamber rather than being displaced, cutting flow rate and system pressure. This develops gradually over months, with symptoms including reduced delivery pressure, system pressure relief cycling, and overheating of recirculated fluid. Root causes include abrasive slurry wear, corrosive fluid attack on bore surfaces, and inadequate filtration. Eternal Gear Rebuilders measures actual clearances with precision dial indicators, machines rotors and housings back to OEM profile, and installs matched components to restore volumetric efficiency to specification.
02
Mechanical Seal Failure and Fluid Leakage
Mechanical seals fail when the rotating face loses contact with the stationary seat, allowing process fluid to escape along the shaft. Early signs include minor weeping at the seal chamber, increasing to continuous dripping or spraying as seal face wear accelerates. Causes include corrosive fluid etching the ceramic or carbon faces, thermal distortion from heat generation, and contamination (sand, scale) jamming the seal gap. Once leakage begins, fluid loss and air ingestion degrade performance rapidly. Eternal Gear Rebuilders removes failed seals, inspects the seal chamber and shaft runout, replaces seals with OEM-equivalent or upgraded materials, and pressure-tests to confirm zero leakage before shipment.
03
Rotor Lobe and Piston Erosion from Cavitation
Cavitation occurs when inlet conditions (suction lift, filter blockage, or low inlet pressure) drop below the vapor pressure of the process fluid. Vapor bubbles collapse in the pumping chamber, creating micro-jets that erode rotor lobes, piston crowns, and bore surfaces. Damage appears as pitting and cratered surfaces visible under magnification, accompanied by noise, vibration, and loss of displacement. The erosion is often concentrated near the inlet port, and progression is accelerated by abrasive particle entrainment. Eternal Gear Rebuilders restores lobe and piston profiles through precision honing, valve plate realignment, and inlet port polishing to eliminate cavitation inception; we also advise on system inlet design to prevent recurrence.
04
Bearing Wear and Radial/Axial Clearance Degradation
Journal bearings and thrust bearings support rotor/plunger loads and maintain precise clearances critical to PD pump performance. Wear from inadequate lubrication, contamination, or extended service life causes radial and axial play to exceed tolerance, allowing rotor wobble and lobe-to-housing rub. Symptoms include increased noise, vibration, and metallic debris in the discharge fluid. As clearance grows, the pump draws higher current (if motor-driven) and loses displacement uniformity. Bearing failure also allows housing bores and bearing surfaces to be damaged by rotor contact. Eternal Gear Rebuilders replaces all bearings with OEM-equivalent roller or sleeve bearings, machines bearing bores to recover runout tolerance, and verifies axial and radial clearance before reassembly and test.
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