Which impellers are more likely to be clogged if stringy material or solids are pumped?

Closed impellers (Two-sides shrouded):

• In the closed or shrouded impellers, the vanes are covered with shrouds (side plates) on both sides
• The back shroud is mounted into the shaft and the front shroud is coupled by the vanes
• This ensures full capacity operation with high efficiency for a prolonged running period
• This type of impeller is meant to pump only clear water, hot water and acids, non-Viscous liquids, oils and chemicals

Semi-open impeller (One-side shrouded):

• It has a plate (shroud) only on the backside
• The design is adapted to industrial pump problems which require a rugged pump to handle liquids containing fibrous material such as paper pulp, sugar molasses and sewage water etc.

Open impeller:

• In open impeller, no shroud or plate is provided on either side i.e. the vanes are open on both sides
• Such pumps are used where the pump has a very rough duty to perform i.e. to handle abrasive liquids such as a mixture of water, sand, pebbles and clay, wherein the solid contents may be as high as 25%.