For pumps which need to handle solids, either open or semi-closed impellers are required. In general the more open the impeller, the larger the solids that will pass through. There is however a trade off as a more open impeller results in a loss of efficiency. The more closed an impeller is, the greater it's pumping efficiency, but the greater also the wear rate if used for pumping solids. For seawater pumps where there may be an appreciable amount of solids, semi closed impellers are recommended.
Some pumps have what is termed a multistage impeller.
Boreholes may still be sunk into such rock, as long as they penetrate fault lines, along which water can flow, but flows are uoften low, unless the faults are wide. Examples include Granite, Bauxite. Impulse Pump See Hydram pump Inbreeding General term used to describe the mating of fish within family groups. Successive inbreeding can lead to deformities and other problems. Can be avoided by keeping stocks of several different families separate and always breeding between families.