Pumping Challenging Fluids with Peristaltic Pumps

Why peristaltic pumps are versatile

Peristaltic pumps are well-known for their ability to accurately and dependably dispense and transfer fluids in many different applications.  In fact, when the right tubing, pump head and drive are chosen, peristaltic pumps are some of the most versatile pump options on the market, as they can

• handle fluids with a high percentage of particulates
• cope well with high viscosity fluids
• accurately move fluids at a wide range of flow rates
• maintain sterility and cleanliness of the fluid path

To this end peristaltic pumps are ideal for many applications including:

• monitoring for the presence of particles in pharmaceutical environments
• dispensing viscous fluids into small containers
• pumping tissue fixative through an examination slide
• transferring glue into a labelling machine
• pumping chemically abrasive substances in food and beverage plants

In these situations, it is worth bearing in mind some key tips when handling particularly difficult fluidic substances, such as those that are abrasive or highly viscous.

Optimise tube life

With peristaltic pumps, the only part of the pump the fluid encounters is the tubing; there are typically no fittings or valves, and therefore virtually no possibility of mechanical parts becoming clogged. Of course, because the tubing is doing much of the mechanical work, it does wear over time. Whilst it is generally inexpensive to replace the tubing, it is always a good idea to take steps to prolong the usable lifetime of the tubing.  To that end, here are some key ways in which tube life can be optimised:

• Choose abrasion-resistant tubing. Norprene^® tubing and PharMed^® BPT have good abrasion resistance. Tygon^® tubing is fair with abrasives, while C-FLEX^®, Silicone, and Viton^® are only moderately resistant to wear from abrasive materials and will thus need to be replaced more often.
• Use an adjustable-occlusion pump head. An adjustable-occlusion pump head can be set to allow a reduction in the amount the tubing is squeezed by the pump’s rollers, allowing easier passage of abrasives with less wear of the tubing (Figure 1, a). The standard occlusion for fixed-occlusion pump heads is set in such a way that hard particles would be pressed into the tubing wall and thus cause premature wear (Figure 1, b).

Figure 1: Partially occluded tubing in comparison to (b) to fully occluded tubing (a)

• Select a larger tubing size. By increasing the internal diameter of the tube it is possible to reduce the rate that particles come into contact with the tubing wall. In general, hard particles should be even smaller in relation to the ID of the tubing (less than 5%) whilst soft particles should have a maximum diameter that is less than 25% of the tubing’s inner diameter (ID) (Figure 2, a and b respectively).

Figure 2: Ratios of tubing in relation to hard particles (a) and soft particles (b)

• Slow down the speed of the drive. Slowing down the speed of the drive will lower the flow rate but it will also result in a gentler pumping action that can be correlated with a longer tubing life. Slowing down the drive speed can also increase the efficiency of the pump when abrasive fluid is being transferred. When combined with a larger tubing inner diameter, the target flow rate can still be achieved whilst also reducing tubing wear.

Viscous fluid behaviour and choosing the right tubing

Effectively transferring viscous fluids can prove difficult. However, the gentle squeezing action of a peristaltic pump makes simple work of transferring fluids regardless of viscosity, so long as the right tubing is selected, and the pump’s operational settings are adjusted accordingly.

To maximise the pumping efficiency of viscous fluids, it is important to consider these key points:

1. Slow down the speed of your pump. The maximum recommended speed of the pump decreases as viscosity increases and tubing size decreases. Therefore, running at slower speeds allows for more predictable behaviour of the pump when viscous fluids are involved.
2. Choose a firm tubing. The performance of firm tubing – like Chem-Durance^® Bio, GORE^® Style 100SC and Style 500, Norprene, PharmaPure^®, PharMed BPT, and Tygon E-LFL – will be better than other softer tubing because the firmer tubing returns to its original shape more quickly after pump head occlusion. This creates a stronger vacuum more rapidly, which in turn allows liquid to be pulled into the tubing more effectively.
3. Select a tubing with a smooth bore. A smooth bore will decrease frictional forces. BioPharm, BioPharm Plus, Tygon E-Lab, Tygon E-LFL, or Silicone formulations are good choices.
4. Decrease the viscosity of your fluid. This can be done by applying heat to your fluid.
5. Choose a larger size tubing than required to pump water. (Figure 3)

Figure 3: Click to enlarge chart

Figure 3: General guideline of minimum tube size in relation to viscosity (cp). All viscosity test data were obtained at a temperature of 21°C and 0 bar of back pressure, using firm tubing materials such as Norprene, PharMed BPT, Viton, and Tygon due to their performance with viscous fluids.

Masterflex^® peristaltic pumps

Masterflex peristaltic pumps are ideally suited for use in applications involving abrasive and viscous fluids. When the right tubing material and size are utilised and the pump’s operation is optimised, tube life is lengthened, and more repeatable pumping results can be achieved.