Viscosity or Density When Selecting 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 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 pump that is too small 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. In fact, the graphics that accompany the manuals of the pumps are made for a given fluid and a certain viscosity.

How does Viscosity or Density affect selecting a pump?

Many times do we have questions or confuse two concepts, perhaps it would be interesting to read their definitions:

Density: to the amount of mass in a given volume of a substance that is defined. Therefore the average density is the ratio of the mass of a body and volume that occupies (p = m/v)

Viscosity: property of fluids that characterize their resistance to flow, due to the friction between its molecules

Is it important therefore to bear in mind these concepts to select a pump?

A very common mistake is to think that all fluids behave similarly to water pumps, and this, which is a mistake, can cause expensive problems.

Let us take an example with oil:

High temperatures, low density, which means that, before the same mass of oil into a container, volume tends to rise. If the container is closed, to not be able to increase the volume, the fluid (in this case oil) tends to raise the pressure even to burst pipes.

At low temperatures, the density of the oil also falls to this not being a big problem for our product.
However at low temperatures, the viscosity of the oil goes up. When choosing a pump, one of the determining factors for the same is the viscosity by what could be the case that the chosen pump might be not suitable.
We need a pump that provides a certain pressure, but if the properties of the liquid are not taken into account, the incorrect pump may be chosen.

On the contrary, selecting a pump that is too large can effect operating cost or take up to much space while a pump to small could not be capable of moving fluid.

In short, we have to take into account with regard to viscosity and density for selection of a pump would be:

Resistance of the liquid to flow
The “sticky” that is fluid and in which conditions is found, will notably influence pump that we select.
Each liquid has its own density and also vary according to the temperature where they are.
Take into account the load or height from which you want to pump the fluid, since those who are heavier, will need more pressure.
With these considerations the selection of the pump will be suitable and will avoid problems much greater later on.