This 13" diameter double-shrouded impeller, for a high-speed sea water pump, is cast in Ferralium® 255 (UNS S32550, Alloy 255, DIN 1.4507, ASTM F61), which offers anti-cavitation advantages that, combined with a fine vane finish, give maximum resistance to that form of attack.
Langley's long experience in casting has built a fine reputation for a very good as-cast finish on impeller vanes, which cannot normally be machined because of their inaccessibility. For high-speed pumps running at 6000 rpm or more, dimensional accuracy of the vane profiles and their finish becomes increasingly critical.
To meet these requirements Langley now uses ceramic cores in the casting of high-speed impellers. This gives an even better as-cast finish to the vanes, and the improved profile uniformity makes final balancing of the impeller easier, with considerably improved hydrodynamics.
