Viscosity and Density matter when selecting a pump

Why does it matter when selecting a pump?

Many times we have questions or we can confuse both concepts, perhaps it is best to go to their definitions: Density is defined as the amount of mass in a given volume of a substance. Therefore the average density is the ratio between the mass of a body and the volume it occupies (p = m / v) Viscosity: property of the fluids that characterize their resistance to flow, due to the friction between their molecules.

Is it important to consider these concepts to select a pump?

ABSOLUTELY! A very common mistake is to think that all fluids flow the same way as water. This mistake, can cause very expensive problems.

Let’s give an example with motor oil:

At high temperatures, the density of motor oil decreases, which means that, with the same mass of oil in a system, the volume of the oil will increase. If the oil system is a closed system, the fluid is unable to increase in volume, the fluid (in this case, oil) pressure will rise in the system, to the point of possibly causing leaks or even bursting the oil lines pipes or equipment.

At low temperatures, the density of the oil also decreases and this is not a big problem for our product.

However at low temperatures, the viscosity of the oil rises. When choosing a pump, one of the determining factors is to determine the viscosity of the product being dispensed, this will lead to the proper pump being selected.

We need a pump that provides a certain pressure to be able to move the product, but if the properties of the liquid to be pumped are not taken into account, it is very possible that we do not choose the correct pump.

Perhaps we select a pump that is too large, with increased acquisition and operating costs or, on the contrary, a too small pump that is not able to move the liquid will cause the pump to fail in delivering product.

In summary, what we have to take into account regarding the viscosity and density for selecting a pump would be:

Resistance of the liquid to flow
The properties of the fluid and depending on what conditions it is in, will have a significant factor on the pump that we must select.
Each liquid has its own density and it will also vary according to the ambient temperature.
Take into account the overall distance and volume you are wanting to dispense. Lubricants that are “heavier” will require a higher pressure ratio pump.

With consideration of all of these factors, the proper selection of the pump can be made and you will avoid many issues.