Centrifugal pumps require priming (filling the casing and suction line with liquid) before startup because they cannot pump air/gas. Below are the common priming methods and best practices:
Centrifugal pumps cannot create suction lift if air is present (unlike positive displacement pumps).
Air causes vapor lock, leading to:
Dry running → Seal/bearing damage
Cavitation → Impeller erosion
Reduced efficiency → Poor flow/pressure
Steps:
Fill the pump casing and suction pipe manually via a priming port.
Open air vents to release trapped air.
Close vents once liquid flows out.
Start the pump.
Best for: Small irrigation pumps, portable units.
How it works:
A foot valve (non-return valve) at the suction inlet prevents backflow.
A priming chamber retains liquid when the pump is off.
Best for: Shallow well pumps, agricultural applications.
How it works:
A vacuum pump extracts air from the casing and suction line.
Creates negative pressure, drawing liquid into the pump.
Once primed, the main pump starts automatically.
Best for: Large process pumps, firefighting systems.
Components:
Priming tank (stores liquid for startup).
Electrically controlled valves (auto-fill function).
Float switch (detects prime loss).
Best for: Municipal water systems, HVAC.
How it works:
A venturi ejector uses compressed air/water to create suction.
Removes air from the pump casing.
Best for: Mines, deep well applications.
| Issue | Possible Cause | Solution |
|---|---|---|
| Pump won’t prime | Air leaks in suction line | Check joints, tighten connections |
| Loses prime quickly | Faulty foot valve | Replace foot valve |
| Excessive priming time | Clogged strainer | Clean suction strainer |
| Cavitation after priming | Low NPSH (Net Positive Suction Head) | Increase liquid level or reduce suction lift |
✔ Ensure no air leaks in suction piping (use Teflon tape on threads).
✔ Install a check valve to prevent backflow when the pump stops.
✔ Use a transparent primer chamber for visual verification.
✔ For dry-running protection, install a low-level cutoff switch.
| Feature | Self-Priming Pump | Non-Self-Priming Pump |
|---|---|---|
| Priming Needed? | No (retains liquid) | Yes (manual/vacuum) |
| Suction Lift | Up to 6-8m | Limited (requires flooded suction) |
| Cost | Higher | Lower |
| Maintenance | More complex seals | Simpler design |
Small pumps → Manual priming or foot valves.
Industrial pumps → Vacuum/auto priming.
Critical systems → Self-priming or ejector-assisted priming.
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