Hazards of Slurry Pump Impeller Reverse Rotation and How to Prevent It

Reverse rotation of a slurry pump impeller can cause severe damage, ranging from the impeller falling off to complete pump failure. The major hazards include the following:

1. Impeller detachment

The impeller of a slurry pump is connected to the shaft through a unidirectional threaded joint. Under normal operating conditions, the impeller tightens itself as the pump rotates, ensuring stable performance.
However, if the pump rotates in the opposite direction, the impeller will loosen immediately and may detach. In this case, the pump must be completely disassembled, inspected, reinstalled, and tested before it can be used again.

2. Damage to wear parts (wet-end parts)

During normal operation, the pump rotates at high speed and its components are heavy. Once reverse rotation occurs, the reaction force pushes the impeller outward, causing it to collide with the volute liner and frame plate liner.
If the speed is high, the impact force becomes strong enough to cause serious damage:

• frame plate liner may break

• volute liner may crack

• impeller vanes may be heavily impacted
  In extreme cases, all wear parts may be destroyed.

3. Mechanical seal damage

Mechanical seals are usually made from materials such as 2Cr13 or 316L, which have high rigidity and poor flexibility.
The mechanical seal consists of a stationary ring fixed on the housing and a rotating ring connected to the shaft.
When reverse rotation occurs and the impeller loosens, the reaction force pushes the shaft backward toward the motor, causing the stationary and rotating rings to collide violently.
This instantaneous impact is extremely damaging and can directly break both the stationary and rotating rings.

4. Pump shaft bending

If the impeller forcefully pushes against the pump shaft during reverse rotation, and if the shaft rigidity is insufficient, the shaft may bend.
A bent shaft will inevitably cause damage to other internal components and lead to long-term operational instability.

5. Increased noise during subsequent operation

Once reverse rotation occurs, the clearances in the transmission system may increase.
If not properly adjusted, the pump may generate loud noise during future operation due to friction between the impeller and liners.

How to Prevent Impeller Reverse Rotation

• Use a keyed connection between the impeller hub and the shaft, and lock the impeller with an impeller nut at the end.
  The impeller nut has a small outer diameter and nearly round shape, reducing torque during backflow and preventing loosening.

• Perform a forward and reverse rotation test before connecting the pump to the motor.

• Ensure that the motor and pump are decoupled during testing to avoid accidental reverse rotation.

• Apply thread adhesive where appropriate to reinforce the connection.

• Slurry pumps usually have a shaft sleeve removal ring, which also helps prevent impeller reverse loosening.

By carefully checking rotation direction and securing the impeller assembly, reverse rotation accidents can be effectively avoided.