When you decide material for the construction of a gear pump, the factors that must be considered are; initial material costs, replacement costs, and shelf life. In addition to considering the liquid itself when choosing a structural material, there are also concentrations, contamination, and temperature of the fluid to consider. Standard materials for pump components such as bronze, cast iron, and mild steel tend to be cheaper initially. However, if these materials lead to premature failure, unexpected repairs, and replacements, the price will be higher. Some low-speed gear pumps may require upgrading the rotor material from cast iron to steel as the viscosity increases to withstand increased torque due to viscosity.