An analysis of shaft/shaft seal interaction of a multiple disk centrifugal blood pump

Abstract

A multiple disk centrifugal blood pump is in the early stages of development. As is the case with most pumps that are shaft driven, leakage problems around the shaft/shaft seal interface are of major interest. If leakage were to occur during or after implantation, potential events such as blood loss, clotting, blood damage, and/or infections could produce adverse effects for the patient. Because of these possibly adverse circumstances, materials and shafts are being evaluated to determine the most appropriate course to limit these effects. Teflon and Nylon were analyzed as potential shaft seal candidates with both a stainless steel shaft and a Melonite 9 coated shaft, the latter provided by Houston Unlimited Inc. Metal Processing in Chappell Hill, Texas. The materials and shafts were evaluated under four time durations (I 5, 3 0, 4 5, and 60 minutes), four rotation rates (800, 1000, 1200, and 1400 RPM), and two outer diameters (0.5" and 0.75"). The three main parameters evaluated were the inner diameter, the inner temperature, and the outer temperature. Statistical comparisons were computed for the shaft seal materials, the shafts, and the outer diameters along with the inner and outer temperatures. The results indicated that time and RPM had no significant effect on wear. Some unexpected information was produced. Most notable was that the coated shaft did not significantly reduce the amount of wear. This testing has provided enough information to suggest the need for either in vitro testing of the shaft seal or examining alternatives such as magnetic suspension or ferrofluidic sealing.