Magnetic drive pumps (also known as mag drive pumps) are widely used in industries such as chemical processing, pharmaceuticals, and wastewater treatment. Their seal-less design prevents leakage, making them ideal for handling hazardous or corrosive fluids.
However, when a magnetic pump fails to deliver liquid — often described as “not pumping,” “no flow,” or “not drawing water” — it can interrupt production and even damage internal components due to dry running.
This article explains the main causes of this issue and provides practical troubleshooting solutions.
1. Suction Line Problems
Common Issues:
Air leakage in the suction line: Worn gaskets or loose flanges allow air to enter, preventing vacuum formation.
Excessive suction lift: The installation height exceeds the pump’s allowable suction head, making it difficult for the liquid to rise.
Blocked pipeline or closed valve: The suction filter, foot valve, or pipeline may be clogged, or a valve may not be fully opened.
✅ Solutions:
Inspect and tighten all suction flanges and joints.
Clean or replace the strainer and foot valve.
Adjust the installation height to ensure the liquid level is above the pump centerline.
2. Air Trapped Inside the Pump
Magnetic drive pumps are non-self-priming. If the pump chamber is not completely filled with liquid before startup, trapped air can prevent liquid from entering the impeller, resulting in zero flow.
✅ Solutions:
Prime the pump fully before starting.
Open the vent plug to release trapped air.
Check for gurgling or bubbling noises — an indication of remaining air.
3. Insufficient Inlet Pressure (Cavitation)
If the suction pressure is too low — especially when pumping high-temperature or volatile liquids — vapor bubbles may form (cavitation), blocking the impeller flow.
✅ Solutions:
Lower the installation height or raise the suction tank level.
Use larger-diameter suction piping to reduce resistance.
Keep liquid temperature below its boiling point at suction pressure.
4. Magnetic Coupling Failure
The magnetic coupling transfers torque from the motor to the impeller. If the magnets are demagnetized, slipping, or the inner magnet is detached, the impeller will stop rotating — causing the pump to stop delivering liquid.
✅ Solutions:
Inspect the magnetic coupling for slippage or demagnetization.
Replace damaged magnet assemblies.
Check the isolation sleeve (containment shell) for cracks or wear.
5. Impeller or Chamber Blockage
Solids, crystals, or debris in the fluid can block the impeller channels or clog the pump chamber, especially during long-term operation.
✅ Solutions:
Dismantle and clean the impeller and containment shell.
Install a pre-filter in the suction line.
Regularly filter process liquids before pumping.
6. Motor Problems or Reverse Rotation
Incorrect wiring causes the motor to run backward.
Motor speed is too low due to electrical faults.
Abnormal voltage or wrong phase sequence.
✅ Solutions:
Check the rotation direction — it must match the arrow on the pump casing.
Measure voltage and current to confirm proper operation.
Repair or replace the motor if necessary.
Preventive Maintenance Tips
Inspect the suction system regularly – ensure tight seals and clean pipelines.
Always fill the pump before starting – never start dry.
Avoid dry running – it can overheat and demagnetize the coupling.
Control fluid temperature and pressure to prevent cavitation.
Monitor bearings and magnetic couplings for early wear or damage.
Conclusion
A magnetic drive pump that fails to pump liquid is usually caused by air blockage, suction issues, internal clogging, or magnetic drive failure.
By following a systematic troubleshooting approach — from the suction line to the pump body, magnetic coupling, and motor — the problem can be quickly identified and resolved, ensuring stable, leak-free operation.