A Peristaltic pump also referred to as hose or tube pump works using positive displacement. Fluid is fed through tubing by rollers that rotate squeezing a flexible tube against the pump housing.
As the roller moves over the tubing, it expands and creates a vacuum to allow more fluid to enter. During operation, at least one roller closes the tubing. Therefore the need for valves is eliminated. The rollers are turned either directly by a motor or by a gearbox.
Peristaltic pumps are ideal for use with corrosive and viscous fluids, as the only part of the pump to come into contact with the fluid is the tubing. With the tubing or the head being easily replaced, the pumps are relatively maintenance-free.
Thomas has eight sizes of pumps with flows ranging from 0.1 ml/min up to 2000 ml/min. Various tube materials are available depending on their compatibility with the media being transferred. Each of the 8 sizes are available in AC or DC (DC pumps are also reversible) and are self-priming.
If the hose pump is driven without a gearbox, changing the motor speed can control the flow. Common motor types for peristaltic pumps include brushed direct current (DC), brushless direct current (BLDC), alternating current (AC) or stepper motors. Typical motor speeds for peristaltic pumps range between 0-400 revolutions per minute. Usually DC and BLDC motors are used together with a gearbox to set speed depending on the flow need. Stepper motor speeds can be regulated by using an external controller board.
Flow rates are proportional to motor speed. This makes peristaltic pumps suitable for dispensing and dosing applications. In order to choose the right motor there are a few aspects to consider. Direct current motors are available in different quality levels ranging from 500 up to 4000 hours of operation. Limiting factors of those motors are the brush system and the bearings. In AC motors lifetime ranges between 1000 hours in shaded pole variants up to more than 10,000 hours in capacitor versions.
When it comes to stepper and brushless DC motors the limiting aspect is usually only the bearing system. In the BLDC and stepper motors the speed can be adjusted during operation very easily. Those motor types are commonly used when a variable flow rate is needed.
Typical peristaltic hose or tube materials range from silicone over thermoplastic vulcanizate (TPV) or PVC to fluoroelastomeric materials. Silicone is commonly used when non-aggressive media need to be pumped. Compared to other materials silicone is on the softer end of the range. TPV combines the easy processability of Polypropylene with the elastomeric properties of EPDM. Commonly used tubing materials based on TPV are PharMed® BPT or Santoprene™. When more chemically corrosive media need to be pumped, fluoroelastomeric materials like Viton® are used.
When it comes to choosing the right tubing the right choice of tubing dimensions is crucial. When maximum tube lifetime is key, a tube with larger inner diameter and low motor speed is advantageous. For higher flow rates large inner diameter tubing and high motor speed should be chosen. When the application requires high accuracy, the tubing should have a minimal inner diameter and motor speed should be high. For pumping viscous liquids tubes should have higher wall thickness to ensure quick recovery of the original shape.
Particles from tubing may be shed into the fluid circle, a process called spallation. Spallation is to be avoided especially in biological, pharmaceutical or medical applications. Special types of TPV materials such as Versalloy™ exist that offer optimized properties to reduce spallation.
In order to reduce pulsation many peristaltic pumps offer a spring-loaded mechanism to ensure smooth pumping action. This feature is also important for shear sensitive fluids such as living cells. Another aspect to consider is the adjustment of the pump to different tube dimensions dependant on the flow rate needed.
The more sophisticated pump types also feature an adjustable occlusion. This feature can help to adjust the pump to different pressure levels that might occur in fluidic systems. Moreover, it helps to adjust the pump performance to different tubing materials. Depending on the type of fluid, softer tubings made out of silicone are used, whereas for chemically demanding applications fluoroelastomeric materials need to be used. Those are usually significantly harder.
Peristaltic pumps stand out due to their ease of use. The tubing or pump head can be replaced in a matter of seconds. The design without the need for internal valves has different advantages. Clockwise and counterclockwise operation is possible, so liquids can be transferred in both directions if the process requires it. As there are no valves, there are less restrictions in the tubing, which helps when viscous media need to be transferred.
To increase efficiency of the product multi-channel peristaltic pumps can be used. In such pumps one motor drives a pump head with up to 15 channels, each containing a separate tube. With that different media can be transferred at the same time or the same medium can be distributed to multiple vessels. The number of rollers used in peristaltic pumps has a major effect on the fluid handling. For higher flow rates only two or three rollers are used. The downside of this is that the pulsation is high. If a gentle transfer of the medium is required, often more rollers are used to maintain a moderate level of pulsation.
An important requirement in many medical or analytical processes is to avoid cross-contamination. The tubes are the only part in contact with the medium and can be switched out easily after each process cycle.
Other applications include detergent dispensing in industrial dishwashers, condensate removal in continuous emissions monitoring or transfer of dialysate in dialysis machines.
Thomas offers pumps with flow rates ranging from smaller than 0.1 ml per minute up to 2000 ml per minute. In special product versions high pressure of up to 10 bar can be handled. Since 2019 Thomas includes customizable and high quality peristaltic pumps by the former manufacturer Oina. This increases the range and possibilities to provide solutions for demanding applications significantly.