TL;DR
Reduced mixing quality is most often a worn or fouled impeller running at the wrong speed. Inspect blade profiles, verify RPM against the design duty sheet, and check impeller submergence.
What you might see
- batch blend time increasing
- settled solids observed at tank bottom
- concentration gradients visible in process samples
- process product quality falling outside spec
Likely causes
Worn or eroded impeller blades reducing pumping capacity
Operating speed changed from the design setpoint after a drive or control system update
Impeller running too close to the surface and entraining air into the batch
Process fluid viscosity higher than the design, requiring more power or a different impeller geometry
Required tools
- Tachometer or VFD readout
- Vernier caliper or tape measure for impeller diameter
- LOTO kit
Safety first
- Lock out the motor disconnect before entering the tank or reaching near the impeller.
- Confined-space procedures apply for any work inside the mixing tank.
Procedure
- 1
Pull the process specification and confirm the required blend time and target impeller speed.
- 2
Stop the mixer and lock out. Inspect the impeller blades for erosion, edge rounding, or missing sections. Compare the blade profile to the installation drawing.
- 3
Measure the impeller diameter. More than 5% reduction from the nominal dimension indicates significant wear.
- 4
Restore power and measure the shaft speed with a tachometer or check the VFD display. Confirm it matches the design RPM.[1]
- 5
Check the impeller submergence depth against the Lightnin installation drawing for this tank geometry. Low liquid level or incorrect impeller position causes air ingestion.[1]
- 6
If the fluid viscosity has changed (new formulation or temperature change), consult the Lightnin application data for the XE frame to determine if a different impeller or increased speed is required.
- 7
Replace worn impeller blades or the complete impeller if wear exceeds 5% diameter loss. Use Lightnin-specified replacements for the XE shaft size.
Sources
SPX Lightnin XE Series Industrial Mixer Installation, Operation & Maintenance Manual, SPX Lightnin
SPX Lightnin XE Series Industrial Mixer Installation, Operation and Maintenance Manual, impeller speed and submergence specifications (general)
View source
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