Increasing the Accuracy of Peristaltic Pumps

There are vast applications of peristaltic pumps because of their simple construction and ease of use. The construction of peristaltic pumps does not allow the liquid being pumped to be exposed to the pump’s mechanism. That helps hospitals using these pumps to circulate blood during bypass surgery as a critical part. Used in heart-lung machines, the design of these pumps prevents significant hemolysis – the rupture of destruction of red blood cells. The chief advantage of the design is the compressible polymer tube through which the dispensing liquid passes.

For fluids that must be isolated from the environment, this simple arrangement works very well. For example, it allows pumping slurries with a high solid content and other aggressive chemicals. However, rollers inside the peristaltic pump produce pulsations as they move an on and off a pressure shoe that compresses the tube. These pulsations prevent accurate dispensing.

Drug development and delivery depends largely on accurate dispensing. For example, accurate dispensing and aspirations are extremely important for addressing safety concerns related to tremendously expensive high-potency compounds such as biotech designer molecules used by leading-edge pharmaceuticals. The proteins and synthetic molecular chains composing these compounds are very fragile and highly susceptible to tear. That calls for short setup times and the dispensing tube meeting or exceeding the safety and contamination concerns. The peristaltic pump finds wide applications because it is able to address the above requirements.

One simple method of reducing the pulsations from the peristaltic pump is to increase the number of rollers. However, that is not a very practical idea. A pump with three rollers can greatly reduce its fluid-dispensing variance provided it has one roller in the same starting position when starting each dispense – the pump repeats its starting position every 180 degrees.

An integrated motor solution with signal inputs and outputs for roller positioning makes this a possibility. The design allows the pump to dispense volumes made from multiple revolutions plus some fraction of a revolution. With roller positioning, it is possible to take into consideration the fraction of the revolution and ignore the complete revolutions. External valves help with the dispensing of fluid from the peristaltic pump to control the starting position of the next roller without dispensing.

In practice, the motor allows the pump to dispense and then operates the valve, allowing the rollers to be positioned to the same starting point for the subsequent dispense cycle. The process ensures a precise and repeatable quantity of dispensing. Usually, drip retention is also used to bring back the fluid into the tube. This is to prevent a drip of the fluid when closing the dispense valve. Usually, that causes a small amount of fluid to be wasted. This can be prevented by repositioning the next roller in a positive or a negative direction to minimize the fluid waste.

Another method is to use multiple tube peristaltic system. The rollers in this system are intentionally offset and the output of the tubes combined. This effectively increases the total number of rollers, minimizing pulsations. Here, one of the legs becomes the waste tube and the dispense valve is positioned after the combined outlet.