Monday, February 21, 2022
All aspects of the process conditions need to be considered when choosing the right peristaltic pump for your application.
A peristaltic pump consists of three components:
It is the interaction of these three components that determines the immediate selection process but more importantly the long-term behaviour.
A peristaltic pump is also referred to as a positive displacement pump. The pump creates a suction by squeezing a small section of tubing and pushing this pinch point along the inside of the pump head. It does this in a continuous motion so that a pinch point is followed be another pinch point creating a small pocket/pillow between the two points. This pillow is usually filled with the liquid which is pulled into the pump head and then pushed out of the pump head which in turn creates the suction and the pumping process.
The pumps motor has a drive shaft which couples directly onto the pump head. Inside the pump head there is system of rollers attached around this central shaft which rotates at the same speed as the drive shaft. The number of rollers inside the head will vary between the different head designs but typically this is between 2 and 10 rollers.
The rollers when rotated around create a pinch point, this point is usually located at the inside top half of the pump head housing. The section of tubing between two rollers is the “pillow”. The greater the distance between two rollers means that the “pillow” is larger, and a larger “pillow” equates to a higher volume of contained liquid, therefore a faster flow.
The rule of thumb is fewer rollers equals a lager “pillow” and more rollers means smaller, which in turn is reflected in the achievable flow rates of a pump head.
The first process condition to be looked at is often the flow rate. This is essentially a combination of pump speed and displaced volume. Speed is defined by the revolutions per minute of the drive, and it is these RPM that are combined with the internal volume of the tubing to determine the flow rate. The volume of liquid contained within the pocket is simply Πr²L where r is the inner radius of the tubing and L is the length of the pocket. Essentially the larger the inner diameter, the greater the volume. Moving this volume faster with a higher RPM drive obviously results in the flow rate being increased. The same is applicable for a slower flow rate; the use of tubing with a smaller ID with a pump head that has more rollers that are closer together results in a smaller pocket volume and this, together with slower revolutions, allows for microfluidic flow rates.
The second consideration is how the pump will be used. The two common uses are either a straightforward Flow Rate type or the more specific Dispensing type. A Flow Rate pump is used for the continuous movement of liquid, for example within Tangential Flow Filtration, whereas a Dispensing Pump is used when filling or dosing a specific volume of liquid, for example when filling vials or bottles. Further consideration is required here with regards to process time and fill volumes and how the operator will use the hardware.
The third consideration is the physical characteristics of the fluid being pumped. What is the fluid, is it corrosive, is it a solvent, what is its temperature and how viscous is it? All of these play a part in the selection of the correct tubing with regards to its size, the wall thickness, its chemical compatibility, and its pressure rating.
Lastly, we need to consider the environmental conditions within which the pump will be located. Aspects such as moisture, temperature, possible chemical fumes, or dust all play a part in selecting the optimum housing for the application.
The 1E series of peristaltic pump is a compact model, ideal for simple operation in your lab or on your bench-top.
Longer pumps L100-1F Series intelligent peristaltic pump for low flow rate applications due to the 100 RPM pump speed.
Our experts at PCT are on-hand to help you find the correct solution for your application. We welcome all enquiries, so please do get in touch.
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