Pump Handbook

Solids and Slurries - Definitions & Applications (Cont.)

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Solids and Slurries - Useful Formulas a. The formula for specific gravity of a solids-liquids mixture or slurry, Sm is: EXAMPLE: If the liquid has a specific gravity of 1.2 and the concentration of solids by weight is 35% with the solids having a specific gravity of 2.2, then: b. Basic relationships among concentration and specific gravities of solid mixtures are shown below: Where pumps are to be applied to mixtures which are both corrosive and abrasive, the predominant factor causing wear should be identified and the materials of construction selected accordingly. This often results in a compromise and in many cases can only be decided as a result of test or operational experience. For any slurry pump application a complete description of the mixture components is required in order to select the correct type of pump and materials of construction. c. Slurry flow requirements can be determined from the expression: EXAMPLE: 2,400 tons of dry solids is processed in 24 hours in water with a specific gravity of 1.0 and the concentration of solids by weight is 30% with the solids having a specific gravity of 2.7 then: d. Abrasive wear: Wear increases rapidly when the particle hardness exceeds that of the metal surfaces being abraded. Always select metals with a higher relative hardness to that of the particle hardness. There is little to be gained by increasing the hardness of the metal unless it can be made to exceed that of the particles. The effective abrasion resistance of any metal will depend on its position on the mohs or knoop hardness scale. Wear increases rapidly when the particle size increases. The life of the pump parts can be extended by choosing the correct materials of construction. Sharp angular particles cause about twice the wear of rounded particles. Austenetic maganese steel is used when pumping large dense solids where the impact is high. Hard irons are used to resist erosion and, to a lesser extent, impact wear. Elastomeric materials are used when pumping concentrations of fine material but total head is usually restricted to about 100 ft. per stage. Castable ceramic materials have excellent resistance to cutting erosion but impeller tip velocities are usually restricted to 100 ft./sec.

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