6 Tips for Pumping Viscous Fluids

Pumping viscous fluids requires special considerations due to increased flow resistance compared to less viscous liquids. If this isn’t mitigated, the scientific process can grind to a halt.

Below we’ll go over several guidelines for more efficiently pumping viscous fluids.

How Pumps for Viscous Fluids Differ

Viscous fluids flow more slowly than non-viscous ones. As such, pumps for viscous liquids must adjust: pumping action must counteract that slowness in order to keep your process productive. Peristaltic (tubing) pumps are ideal for pumping viscous fluids.

Furthermore, selecting the proper size and type of tubing for pumping viscous fluids is an inexact science. Experimentation is likely the best way to find the ideal tubing for your application.

You don’t have to take a complete shot in the dark, however. Check out these guidelines to maximize efficiency pumping viscous liquids.

Guidelines for Pumping Viscous Fluids

  • Slow down the speed of your pump. Fluid will only move into the pump head up to a particular rate. Once this rate is achieved, increasing the motor speed will not increase flow rate. The maximum speed the system will pump efficiently decreases as viscosity increases and as tubing size decreases.
  • Choose a larger size tubing than what is required for pumping water. Choose approximate flow rates of various viscosity fluids at 100 rpm for different sizes of Masterflex® L/S pump tubing. To find the viscosity of the fluid you will be pumping, go across the graph horizontally to the flow rate you require and select the next larger size tubing. Using a larger tubing size allows you to run the pump efficiently at higher drive speeds.
  • Choose a firm tubing with a thick wall such as Norprene®, Viton® or Tygon®. Performance will be better because the tubing springs back into its original shape quicker after it is occluded in the pump head. This allows the liquid to be pulled into the tubing with greater force.
  • Select a tubing with a smooth bore. This will decrease the frictional forces. Tygon or silicone are good choices.
  • Pressurize the inlet to your pump slightly [less than 15-20psi (1-1.4bar)]. This will keep the inlet tubing full and allow more efficient pumping.
  • Decrease the viscosity of your fluid. Heat your fluid if possible, viscosity usually decreases with temperature. Learn more

Finding the right pumps for your viscous fluids

To a certain extent, finding the right pump for thick liquids is a matter of trial and error. But our guide can help you make data-based decisions regarding where to start. Learn more about pumps handling various viscosity characteristics.

Click to see flow curves at various viscosities for the recommended L/S tubing sizes for that viscosity. We do not advise using a smaller size tubing than what is shown in the graphs, but a larger size is acceptable. Remember that increasing the tubing size will increase your flow rate because the loss due to friction is decreased with a larger I.D. Not only will the fluid flow more easily, but a higher drive speed can be used without loss of efficiency.

The data in this application tip was compiled using Norprene tubing, the appropriate Easy-Load® pump head, and viscosity standards at 25°C. The inlet and the outlet were 2.5 horizontal ft (0.75m) from the pump (no suction lift or discharge head).

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