pumps

Cole-Parmer asked our UK expert, Colin Heathfield, Technical Sales Manager, to answer some of our most-asked questions. Q: When transporting fluid, what are the biggest challenges involved? A: For customers looking to transfer fluid, selecting pump technology that provides the best fit for their application is one of the biggest challenges. Over the years I have been involved in pumping a wide range of media—from water to liquid glass to aggressive chemicals and sensitive biological solutions. I start by considering the overall process rather than just a specific component. I then look at the pumping function, including where the fluid is coming from and going to, and identify process conditions. I also consider the fluid’s chemical attributes: temperature, specific gravity, viscosity, and whether it is clean, has particulates or soft solids or is shear sensitive. I then consider physical requirements including flow rate, discharge and system pressure, and suction conditions. Q: Can you cite an example of a problem that could occur and what the solution would be? A: A difficult liquid could be part of a bioprocess where the liquid is shear sensitive. This means if the pumping action is too vigorous or "violent," it will damage the fluid and not deliver the required outcome. For media containing bacteria or other living cells, this can result in damaged cells. These conditions would negate several pump technologies with rotating internal components, such as impellers or meshing gears that mechanically impact the fluid. For these types of applications, I would recommend a technology with a more gentle pumping action such as a peristaltic pump. Q: Are there technical solutions involved and, if so, what do they entail? A: As in the example above, a successful installation will require a pump capable of being shear sensitive and maintaining fluid integrity to avoid contamination issues. For this type of application, I would use Masterflex® peristaltic pump. Its pumping action is shear sensitive and it is a popular choice for moving cell cultures. The pump works like the oesophagus or intestinal tract. A rotating rotor with several independent rollers alternately squeezes and relaxes a length of flexible tubing. As the tubing relaxes, it creates a slight vacuum which sucks fluid into the tube, then as the next roller passes over the tube it pushes the fluid forward. These trapped pockets of fluid continue moving forward through the tube producing flow. The nature of this process means that the velocity of the liquid can be quite low and the fluid is moved "gently" as a positive displacement. The peristaltic pump is sometimes referred to as a tube pump as the media is confined to the tube and it does not come in contact with any other part of the pump. It offers one of the best methods for maintaining system integrity within the process. In recent years, we’ve seen major enhancements to tubing compatibility, pressure, and lifetime performance. Twenty or more tubing formulations are available, each with unique characteristics. These different formulations also ensure that we can offer one that will be chemically compatible with the fluid pumped. Many formulations meet EP and USP regulations and are FDA compliant , making them ideal for pharma and food industries. Q: Aside from the fluid type you chose, what other industries transport fluids? A: We work with Academia, Research & Development (R&D), Chemical, Food and Beverage, Biotech and Pharmaceuticals, Industrial and Manufacturing, Paints and Inks, Petroleum, Water and Waste Water industries. As fluid handling specialists, our core strength is in metering, dosing/dispensing applications. In addition to supplying the pump technology, our experience is in providing complete system solutions including process monitoring equipment (such as conductivity, dissolved oxygen, pH, pressure and temperature transmitters and controllers), homogenizing and mixing equipment, and flow monitoring and control. For customers starting in R&D, we provide advice on pumping and mixing technologies which enable them to scale-up their work to the pilot and process plant. Q: What problem could arise and what is a possible approach to fixing the problem? A: An interesting application we worked with involved corrosion testing. A test solution of sodium chloride and water with small iron fines was pumped around a test circuit at a rate of several millimetres per minute for extended periods of time. This is challenging from a pumping perspective because sodium chloride is chemically aggressive, the iron fines can damage or clog a pump, and the process required accurate and repeatable flow rate for the test results to be valid. We addressed this by selecting a small, valveless piston pump. Chemical compatibility was achieved by selecting a piston pump with a PVDF body and a ceramic plunger. By mounting the pump head vertically for the reciprocating motion, with the fluid flowing left to right, we could ensure that no damage would occur from the fines. By selecting the correct piston diameter, we could maintain sufficient velocity in the fluid to transport the fines. The accurate flow could be achieved by adjusting the speed of the drive or the sweep length of the piston stroke. The choice of a valveless piston ensured there would be no abrasion or reliability issues.

pumps

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