Both semi open and closed impellers are used in slurry services. The control of leakage back into suction is usually accomplished with a combination of clearing or expelling vanes on the impeller and close axial clearances. Because these axial clearances increase with wear, pumps should be arranged to allow simple clearance adjustments to maintain performance.
Close radial clearances wear quickly when solids are present and cannot be conveniently corrected with external adjustment, and should only be used on low concentrations of fine slurries. An axial clearance arrangement between the impeller inlet diameter and liner is common for providing leakage control for high-wear services. Impeller attachment methods vary by manufacturer and service requirements. Various bolted designs and threaded designs are used successfully.
When pumping highly abrasive slurries, the impeller attachment should be protected from wear to optimize service life. An internally threaded impeller is typically used in high-wear services to provide this protection. Balancing requirements for slurry pump impellers are different than those applied to impellers for clear liquids. An impeller balanced for clear-liquid service is expected to remain substantially in balance for most of its operating life.
As a slurry pump impeller wears in service, it will naturally begin to change its balance due to the erosion of metal along the wear surfaces. Consequently, the bearings and shafts in a slurry pump must be designed for a large amount of unbalance in the impeller.
In general, slurry pump impellers will be balanced to a lesser standard (higher residual unbalance) than a clear-liquid impeller. The levels of residual unbalance allowed are determined by the manufacturer and are based on a number of operational and design factors.
Close radial clearances wear quickly when solids are present and cannot be conveniently corrected with external adjustment, and should only be used on low concentrations of fine slurries. An axial clearance arrangement between the impeller inlet diameter and liner is common for providing leakage control for high-wear services. Impeller attachment methods vary by manufacturer and service requirements. Various bolted designs and threaded designs are used successfully.
When pumping highly abrasive slurries, the impeller attachment should be protected from wear to optimize service life. An internally threaded impeller is typically used in high-wear services to provide this protection. Balancing requirements for slurry pump impellers are different than those applied to impellers for clear liquids. An impeller balanced for clear-liquid service is expected to remain substantially in balance for most of its operating life.
As a slurry pump impeller wears in service, it will naturally begin to change its balance due to the erosion of metal along the wear surfaces. Consequently, the bearings and shafts in a slurry pump must be designed for a large amount of unbalance in the impeller.
In general, slurry pump impellers will be balanced to a lesser standard (higher residual unbalance) than a clear-liquid impeller. The levels of residual unbalance allowed are determined by the manufacturer and are based on a number of operational and design factors.