While peristalsis is the organic process, peristaltic pumps are actually positive displacement pumps used in a number of applications to transfer fluids from a point of high pressure to a point of low pressure.
Chemical, laboratory, medical, pharmaceutical, sewage treatment, painting, construction, packaging, agriculture, pulp and paper, water treatment and engineering facilities make frequent use of peristaltic pumping systems. Like all metering equipment, these pumps are designed to introduce a consistent and cyclical flow of liquid into a process stream in order to maintain the homogeneity of the final product or solution. The operation is unique among liquid pumps.
Although specific devices vary, the general function is similar. A length of flexible tubing is wound around a circular track which circumnavigates the pump head. One or more rollers are attached to the cylindrical center and used to compress the tubing at variable intervals. As the rollers move along they displace the fluids within the tube which are then exhausted through a release valve. When the roller is removed, the tube expands to its original volume creating a vacuum which pulls more fluid into the device and the cycle repeats.
Unlike many other types of pumps, including bellows pumps, diaphragm metering pumps and piston metering pumps; the pumping mechanism of the peristaltic pump never makes contact with the fluids it dispenses. This makes its use preferred in applications where sterile liquids are required such as medical and food and beverage processing.
There are three common operational designs associated with the peristaltic pump. Fixed occlusion pumps have a set interval at which rollers are placed and a set pressure which they may apply. This allows for little variation in tube size and material, but does provide constant pressure and consistent performance. Spring loaded roller pumps allow for more variation in materials and flow rates. These offer constant stress operation but adjust to the different sized tubes that may be used for different manufacturing processes.
The third type of peristaltic pump design is what is known as 360 degree eccentric. These mechanisms have a single over-sized roller that undergoes a complete revolution, compressing the tubing along the way. This particular design can increase flow per revolution up to 55% as compared to alternative designs of the same size. Though not always applicable, this third option also reduces the wear and friction on the tubing as it undergoes just one compression per revolution while others may experience stress three or four times during a single operation.
The heat and wear resistance of the particular tubing chosen for a pumping application such as this is very important. Extruded elastomeric materials such as silicone rubber and fluoropolymer are used as they maintain a circular cross-section despite multiple compressions. Chemical compatibility between the hoses and the fluids they will process is also of great importance. Further considerations include inner and outer diameter, pump drive or power source, flow rate, number of rollers and wall thickness.