Rotary lobe pumps are commonly used in the biotechnology industry for a variety of purposes. Shear damage to animal cells within the rotary lobe pump can adversely affect the product yield or purity during, for example, cell concentration via cross-flow filtration. In this research, CHO cells grown in 20L bioreactors where fed to a rotary lobe pump and both single pass and recycle experiments were conducted at different RPMs and back pressures. The results indicate that the slip flow rate more severely impacts the viability of the CHO cells than the pump RPM. Preliminary results also suggest that a low ratio of the net flow rate to the amount of slip has detrimental effects on the cell viability. Hence a mathematical model is presented which recommends the use of a cell death rate constant, K, which accounts for the RPM, net flow rates, amount of slip, back pressures and more importantly the time of exposure of the cells to the shear environment. Based on this model we can attribute a cell death rate constant to a cell line for a given pump and use this constant to compare pump performance from the cell viability point of view. The model also gives a better insight into pump design and selection as it indicates that a smaller pump with higher efficiency and higher RPM might be better than a larger pump with lower efficiency and lower RPM.