Peristaltic Pumps Information
Peristaltic pumps are positive displacement pumps which use rotating rollers pressed against special flexible tubing to create a pressurized flow. The tubing isolates the fluid from the rest of the pump and environment, eliminating contamination and making it ideal for handling aggressive, corrosive, or abrasive media. The roller mechanism also provides low shear pumping of the fluid for shear-sensitive fluids.
Peristaltic Pump Operation
Peristaltic pumps are positive displacement pumps, meaning they use expanding and contracting chambers (in this case hosing) to move fluids at a fixed rate. To learn more about selecting different types of positive displacement pumps, visit the Positive Displacement Pumps Selection Guide page on Engineering360.
Peristaltic pumps consist of a tube which is squeezed by a set of rollers or shoes to move fluid. By constricting the tube and increasing the low-pressure volume, a vacuum is created to pull the liquid into the tube. Once in the pump, the liquid is pushed through by compressing the tube at a number of points in contact with the rollers or shoes. The media is moved through the tube with each rotating or oscillating motion. The design of these pumps is either rotary (circular) or linear.
Peristaltic pump operation. Image Credit: Cole-Parmer
Peristaltic pumps are typically classified based on the pressure ratings they obtain.
Low pressure peristaltic pumps are laboratory grade pumps designed for low pressure pumping applications such as in IVs (medical fluids) and chemical metering. These pumps usually have dry and non-reinforced casings and use rollers to provide the compressive force.
High pressure peristaltic pumps are industrial grade pumps designed for high pressure pumping of aggressive sewage and slurries. The casings in these pumps are lined with lubricants to avoid damage from abrasion and friction, as well as to dissipate heat buildup. They use reinforced tubes designed to handle the high pressures (up to 16 bar).
The most specifications provided by a manufacturer for a peristaltic pump are either related to design or performance.
A number of design parameters should be considered when selecting peristaltic pumps.
Tubing size - the diameter and wall thickness of the casing used to house the media, typically given in inches (in) or millimeters (mm). It affects the discharge and the size of tubing needed for replacement. Pumps may be designed to allow multiple sizes of tubing.
Number of rollers - the number of rollers or shoes used in the drive mechanism. More rollers reduce pulsation and provide a smoother flow.
Number of channels - the number of separate tubes in the pump which operate simultaneously.
The primary specifications to consider when selecting peristaltic pumps are flowrate, pressure, horsepower, power rating, outlet diameter, and operating temperature. For a more in depth look at these specifications, visit Engineering360's Pump Flow page.
Peristaltic Pump Tubing
The compatibility of a peristaltic pump with a certain type of fluid is almost completely dependent on the design of the tubing. This is why, when selecting a peristaltic pump, it is important not to overlook the selection of the pump tubing. There are many factors that should be considered in this selection process.
Chemical compatibility - the tubing material must be chemically compatible with the pumped fluid. Engineers should use a chemical compatibility chart designed specifically for pump tubing (not a general use chart) to aid in this decision. When a chart is not sufficient, immersion tests may be used to determine its compatibility or resistance to corrosion. For some applications, it is better to line the inner part of the tubing with a chemically inert material to maintain both structural and chemical compatibility.
Pressure - the tubing material must be able to withstand the system pressure without leakage or failure. It must also be able to adequately handle abrasive media and suspended solids.
Temperature - the tubing material must be able to operate within the temperature range of the system. Users should identify the minimum and maximum temperatures reached in the system and select a material with an appropriate corresponding temperature range.
Size - the tubing must be correctly sized in order to fit within the pump head and operate effectively. Closer dimensional tolerances will result in more consistent and repeatable performance.
Life expectancy - the tubing material must have a tolerable rated life expectancy to reduce downtime and costs associated with replacement.
Transparency - if the media needs to be viewed during pumping, the tubing material should be transparent.
Gas permeability - for application where the media must be isolated from gases in the environment, the tubing material must have an acceptably low gas permeability rating.
Regulatory approval - for certain industries, such in pharmaceuticals, the tubing material must meet and conform to certain standards and certifications.
A few tube materials include:
Silicone - A translucent medical/food grade tubing which is odorless, non-toxic, and has FDA and USP Class Vl approvals. It is autoclavable and has a temperature range up to 220°C. Used in most general applications.
Autoprene - This is an opaque thermo-plastic rubber with unmatched wear resistance when long tube life is required. This material has FDA food grade approval, and has been further enhanced to meet the requirements and approval standards of USP Class VI criteria for medical bio-compatibility.
Viton - A black, shiny, synthetic rubber with resistance to concentrated acids, solvents, ozone, radiation and temperatures up to 200o C. Viton is expensive, and while it has excellent chemical compatibility, Viton is not renowned for durability and will have a limited service life.
Tygon - This tube has excellent chemical resistance, handles virtually any inorganic chemical, and is one of the family of non-toxic tubes. Tygon has a clear finish and is available in a limited size range.
Prothane II - A transparent blue polyester polyurethane tubing which is resistant to ozone, diesel fuel, kerosene, motor oil, mild solvents, aromatic hydrocarbons, petrol and concentrated acid and alkaline solutions.
Vinyl - The least expensive of any pump tubing type, but is not widely chemically compatible and has a below average service life. It cannot be autoclaved and cannot handle temperatures above 80°C.
Fluoropolymer - The most chemically inert tubing material, but with an extremely short service life. It is autoclavable.
Omega Engineering, Inc. | Hach Company