Weak tank mixing usually comes from one of six causes: insufficient pressure at the eductor, inadequate motive flow, a blocked or worn passage, unbalanced header branches, poor placement, or a process condition outside the original design. Troubleshoot in that order—from measurements to inspection—before adding units or replacing the pump.
Before troubleshooting
Follow the site’s isolation, depressurization, chemical-handling and confined-space procedures. An eductor system can involve pressurized liquid, hazardous chemistry and submerged equipment. Do not open piping or enter a vessel without the responsible facility’s approved procedure.
Collect the original design basis, selected model data, pump curve, piping drawing, normal valve positions and any commissioning measurements. Without a baseline, it is difficult to distinguish a design limitation from a new fault.
Symptoms, likely causes and first checks
| Symptom | Likely causes | First checks |
|---|---|---|
| All eductors appear weak | Pump operating point changed, valve partly closed, filter loaded, low tank level, higher viscosity | Measure pump suction/discharge and header pressure; check flow and differential pressure. |
| Only distant branches are weak | Header friction, asymmetric branch losses, blockage or balancing error | Compare near and far branch pressures. |
| Good surface motion but slow blend test | Short-circuiting, vertical stratification, hidden dead zone | Sample multiple elevations and review orientation. |
| Performance deteriorates over time | Strainer loading, deposits, wear, solids accumulation or pump degradation | Trend pressure, flow and inspection condition. |
| Air appears in circulation | Low submergence, vortexing, suction leak or pump cavitation | Check liquid level, suction conditions and local flow pattern. |
| Unexpected vibration or noise | Cavitation, loose support, unstable flow or mechanical interference | Stop if required by site procedure and inspect the hydraulic condition and supports. |
Seven-step diagnostic sequence
1. Verify the process condition
Record tank level, temperature, density, viscosity, solids concentration and the current mixing objective. Compare them with the original design range.
2. Check valve line-up and pump status
Confirm suction, discharge, bypass and branch valves are in their documented positions. Record pump speed, motor condition and available curve information.
3. Measure pressure at useful locations
Measure near the pump and near representative eductors. A normal pump discharge reading with low header pressure points toward losses between those locations.
4. Check flow or infer it carefully
Use a calibrated flow measurement where available. If flow is inferred from pressure, use the selected model’s current performance data and account for liquid properties.
5. Inspect filters and passages
Compare clean and dirty differential pressure, then isolate equipment according to site procedure before inspection. Deposits can reduce area without creating a complete blockage.
6. Review branch balance and orientation
Compare pressure across branches and confirm no unit has rotated, loosened or become obstructed by nearby equipment. Use the placement and orientation guide.
7. Repeat the process acceptance test
After correction, repeat the same multi-point concentration or temperature test used for acceptance. Surface motion alone is not a release criterion.
Process changes that can look like equipment failure
- A new liquid has higher viscosity or a larger density difference.
- The minimum operating level is lower than the design basis.
- Solids size, concentration or settling rate increased.
- A heat exchanger, filter or additional branch increased system loss.
- The injection point moved into a weak circulation zone.
- The required blend uniformity or completion time became more demanding.
If the design basis changed, re-run the sizing calculation and pump review instead of treating the problem only as maintenance.
What to record after correction
- Date, tank level and process liquid
- Pump speed and measured operating point
- Header and representative branch pressures
- Filter differential pressure
- Eductor model, quantity, position and angle
- Inspection findings and parts replaced
- Multi-point test method and completion time
This record becomes the baseline for future troubleshooting and helps distinguish gradual wear from a sudden process change.
Review the Tank Mixing Eductor Nozzle selection inputs or send Jeltecn the measurements and tank layout for diagnosis.
Technical reference
Spraying Systems Co. notes that tank mixing eductors are offered in different styles, sizes and materials and that correct specification and installation are important to mixing performance: Guide to Optimizing In-Tank Agitation and Mixing Using Eductors.