The construction of closed impellers includes additional back and front walls on both sides of vanes that enhances its strength. This also reduces the thrust load on the shaft, increasing bearing life and reliability and reducing shafting cost. However, this more complicated design, including the use of additional wear rings, makes closed impellers more difficult to manufacture and more expensive than open impellers. A closed impellers efficiency decreases as wear ring clearance increases with use. However, adjustment of impeller bowl clearance does not affect the wear on vanes as critically as open impeller. Closed impellers can be used on a wider range specific speed than open impellers. They are generally used in large pumps and clear water applications. These impellers cant perform effectively with solids and become difficult to clean if clogged.