Choosing the right pump

The media that needs to be transported is very important when choosing a pump as the characteristics of the pump depend on its viscosity (i.e. the fluid’s resistance to a uniform flow), its suction temperature and whether or not there are solid elements in it. You will need to determine if the media to be transported is chemically neutral or corrosive  in order to choose the pump designed to operate under these conditions.

As a general rule, the more viscous the media, the more difficult the flow through your pumping system, but be careful, the viscosity of media varies according to operating conditions. There are 4 main groups of fluids according to their viscosity level; in the first group there are fluids such as water, oil or alcohol that move in the same way regardless of speed or level of agitation. For these types of uses you will not have many constraints in choosing your pump. In the second group there are certain food products such as butter or cream whose viscosity increases with agitation; therefore, in these cases, a standard centrifugal pump will not be suitable for the fluid flow. The third group includes media that has a threshold to be exceeded before flowing. Once this point is reached, the viscosity decreases with agitation. Adhesives, paints and greases are part of the fourth group that are very thick at rest, but their viscosity decreases if constant agitation is maintained.

Generally, for low viscosity fluids (the first and second group) centrifugal pumps are the most suitable because the pumping action generates a high shear rate of the fluid, as the viscosity increases you will have to take into account the additional resistance that the fluid will exert on the shear rate. On the other hand positive-displacement pumps are the best choice for viscous fluids (the third and fourth group) because they operate at lower speeds and the shear energy transferred to the fluids is lower than that of centrifugal pumps.