VANE PASSING SYNDROME CAVITATION V004
A type of cavitation caused by the impeller to cutwater clearance being too small.
You will notice damage to the tip of the impeller caused by its passing too close to the pump cutwater. The velocity of the liquid increases if the clearance is too small, lowering the pressure and causing local vaporization.
The bubbles collapse just beyond the cutwater and there is where you should look for volute damage. You will need a flashlight and mirror to see the damage unless it has penetrated to the outside of the volute.
The damage is limited to the center of the impeller vane and does not extend into the shrouds. You can prevent this problem if you keep a minimum impeller tip to cutwater clearance of 4% of the impeller diameter in the smaller impeller sizes (less than 14′ or 355 mm.), and 6% in the larger impeller sizes (greater than 14″ or 355 mm.).
To prevent excessive shaft movement in closed impeller pumps, bulkhead rings can be installed in the suction eye.
At the discharge, support rings can be manufactured to extend from the walls to the impeller shrouds.
- Vaporization cavitation.
- Air ingestion (acts like cavitation).
- Internal recirculation cavitation.
- Flow turbulence cavitation.