Peristaltic Pumps for Liquids
The Boxer peristaltic pump portfolio extends from a flow of 2 µl/min to 3.5 l/min across 9 platforms. Solutions and sub-assemblies are offered fully customised based on this range or indeed developed completely new. Additionally 3 table top dispensers are offered as complete plug-and-play systems.
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› Flow to 50 ml/min x 1 to 12 Channels
› High precision dosing
› Channel-to-channel calibration
› Driver with optical rotor position sensor
› Tubing cassettes
Complete Product Overview
A peristaltic pump works through the principle of multiple rollers compressing a tube as they rotate around a partial circumference inside a pump body. Between the rollers a chamber of liquid is trapped, and it is transferred from the inlet side to the outlet side of the peristaltic pump. The rollers and roller positions are designed in such a way that the roller on the inlet side occludes the tube before the roller on the outlet side moves away from the tube on the outlet side. Peristalsis is the medical term for muscular contractions of the digestive track in a wavelike motion. The peristaltic pump replicates this motion and is the origin of its name.
A peristaltic pump has the unique feature that the media comes into contact with only the tube. With alternative pump technologies the so called ‘wetted parts’ includes valves, pump bodies, diaphragms etc. These parts are difficult to clean in comparison to a peristaltic pump, which requires only flushing with a neutral media or replacement of the tube. Additionally, chemical compatibility of a peristaltic pump is a matter of checking against the tube material rather than a longer list of wetted parts.
The peristaltic pump tube is critical in determining the pumps characteristics. Due to the principle of how a peristaltic pump operates, the tube must have sufficient elasticity over a long period of time to open once the roller moves away. A peristaltic pump running at 300 rpm with 3 rollers will compress the tube over 50 million times in 1000 hours of operation. Special tubing has been developed for peristaltic pumps and is generally based around thermoplastic elastomers. Additionally, the tube must be correctly sized for a specific peristaltic pump. The wall thickness of the tube is critical since the internal dimensions of the pump are designed to occlude the tube. So, for example if a peristaltic pump is designed for 1.6 mm wall tubing, a 1.0 mm wall tubing will not occlude in the same pump and a pumping motion will not occur. Also due to physical limitation of size and motor torque, the tubing size should always stay within the internal diameter range specified for a particular peristaltic pump series.
Choice of Motors
In many applications the flow of a peristaltic pump is controlled accurately by knowing the speed at which the rollers pass over the tube. The roller assembly is either driven directly from the motor shaft or via a gearbox between the motor and peristaltic pump head. For the greatest accuracy and controllability, a peristaltic pump is most often driven directly by a stepper motor. Such motors allow the user to precisely control the peristaltic pump speed (typically between 0 and 500 rpm) and direction. These motors are generally a 2-phase bipolar construction and require a separate external driver to generate the correct sequencing signal to the motor coils. The alternative is to drive the peristaltic pump via a DC motor with gearbox. They have the advantage of not requiring a separate driver, however the minimum speed is limited to approximately 50% of the peristaltic pump’s nominal or full speed. Both DC motor and some stepper motor peristaltic pumps are available with an encoder to provide a signal output providing speed (and therefore) flow information.
Exchange of Tubing
In many applications the tubing inside the peristaltic pump will be changed frequently over the life of the pump. Design vary from a cassette style whereby the peristaltic pump is opened, and a new tube set or length of continuous tube is replaced, or a flip-top style whereby the pump is partially opened via a lever and new piece of tube is laid through the guides and rollers.
The flow of a peristaltic is said to pulsate. This is actually an interruption, or partial interruption, of flow as the roller moves away from the tube at the outlet. During this part of rotation the flow inside the peristaltic pump is filling the tube as it opens rather than producing flow at the output. The level of pulsation is determined by the geometry of the peristaltic pump’s design. More rollers inside the head decrease the level of pulsation, which improves peristaltic pump accuracy for low volume dosing, however the general flow of the pump will also decrease since the additional rollers pinching the tube reduce the internal pumping volume inside the tube.
Boxer’s range of peristaltic pumps start with the 9QQ and 9QX series producing flow to 200 ml using tubing of ID from 0.5 mm to 3.5 mm and 1.0 mm wall. The peristaltic pump tube options in these series are either tube sets, continuous tube, or flip-top exchange. At the upper end of the range is the 25K peristaltic pump with flows to 2000 ml/min. This peristaltic pump range uses flip-top tube exchange for tubing from 2.4 to 8.0 mm ID and 1.6 or 2.4 mm wall thickness. The 15KS and 15QQ offer a mid-sized peristaltic pump range with wide choice of motors, and finally the 6K and 6KP series of peristaltic pump are a multichannel devices which up to 12 channel driven by a single motor.