Effect of surface roughness of mechanical seals for rotary blood pumps under blood sealing

A miniature mechanical seal with the cooling water circulating system has been developed as a solution of the shaft seal problems in rotary blood pumps. The present paper describes the effect of the surface roughness in the sealing gap on the shaft seal problems under blood sealing. The sealing surface roughness of tested three seat rings were designed to be Ra=0.009, 0.088 and 0.170μm. The frictional loss torque in the sealing gap and the leakage of the blood and the cooling water were measured in this work. Results show that the maximum frictional loss torque measured in the seat ring of Ra=0.009μm, and the frictional loss torque decreased as the surface roughness increased. The leakage rate of the cooling water is larger than that of the blood in all seat rings, even though the blood chamber has higher pressure. The sealing characteristics between under the blood and water sealing were different. Moreover, the best surface roughness in the torque and the leakage characteristics were also different. Thus, it is important to study under blood sealing in the design of the surface roughness of the mechanical seals for rotary blood pumps.