Peristaltic Pumps Answer the Challenge

Peristaltic Pumps Answer the Challenge of Multiple-Channel Pumping


Peristaltic tubing pumps are the flexible and economical solution to multichannel fluid transfer applications.

Introduction to Multichannel Peristaltic Pumps


Technicians in research laboratories and process facilities often need to pump several fluid channels simultaneously. Affordable, space-saving solutions to these applications can save considerable time and resources, while greatly improving process efficiency.

Synchronous control of multiple channels can provide a number of benefits. Varying the speed of the motor will simultaneously and proportionately vary the flow in all channels. The use of a single drive motor can significantly reduce the cost per channel. It can also reduce the total energy requirements, the number of moving parts, and the size and space requirements of the pumping system. The combined result will be a fluid handling system that is economical to acquire, operate, and maintain.

Masterflex Multichannel peristaltic pump

Peristaltic tubing pumps are an extremely efficient and cost-effective option for multiple channel pumping. Peristaltic pumps are available with a wide range of interchangeable pump heads, drives, and tubing.

Multichannel peristaltic pumps are used successfully in a variety of industries including pharmaceutical, chemical processing, biotech, food processing, printing, agriculture, and water treatment. Applications, besides general fluid transfer, include metering and dispensing. (Fig. 1).

The most significant advantage of the peristaltic pump is the use of flexible tubing as the pump chamber. The fluid being pumped remains inside the tubing at all times-the tubing is the only wetted part of the pump. This feature greatly reduces the risk of contamination and gives you extraordinary control over the content and purity of the fluid and over the integrity of your process.

Maintenance, cleanup, and fluid changeover times are all minimized and one pump can transfer several different fluids simply by changing the tubing. The peristaltic pump provides gentle transfer of sensitive and challenging fluids including gases, viscous liquids, and mixed phase fluids such as gas/liquid and solid/liquid combinations.

Pump specification and selection criteria include: fluid flow rates, fluid characteristics, chemical compatibility of tubing, ease of tubing changes, flexibility in pump design (for example, stackable versus cartridge heads), overall accuracy and accuracy between channels, torque requirements, and drive control features. Read on for a look at several of these selection criteria in greater detail.

Pump Tubing and Fluid Characteristics


The flow rate and fluid dynamics through a peristaltic pump are affected by the dimensions of the tubing, the design of the pump manifold, the geometry of the tube occlusion bed, the number of rollers, and by the overall diameter of the roller assembly. As a result, each combination of tubing and pump head type exhibits a unique set of performance characteristics.

  • Pump Tubing

    Tubing size (specifically the inside diameter or ID) is directly proportional to the flow rate in all pump heads. Larger tubing sizes and larger diameter rotors have a greater "pillow" volume (the fluid space in the tubing between adjacent rollers in the pump head). This volume determines the flow per revolution of the pump head.

    To ensure accuracy, it is important to use high-tolerance precision pump tubing and to calibrate the pump. "High tolerance" means that the internal diameter and wall thickness of the tubing have been held within very narrow tolerance limits during manufacture. Minimal variations in the dimensions of the tubing translate directly into minimal variations in flow rate. Calibrating the pump; by adjusting motor speed, run time, or occlusion (the squeezing force applied to the tubing); will further reduce variation and improve repeatability. Always calibrate the pump under actual application conditions (fluid type, temperature, etc.).

    Most tubing materials have a break-in period, during which the shape memory of the tubing and the fluid flow rate adjust and stabilize. The length of this break-in period varies depending upon the tubing size and material. For high accuracy, operate a pump fitted with new pump tubing for at least 10 to 15 minutes before calibrating the flow through individual channels.

  • Manifolds

    It is possible to use the flow channels of multichannel pumps independently, or to manifold them together with Y-connectors. When a manifold is constructed to provide a common inlet or outlet for several tubes, it reduces the number of plumbing lines from the source or to the receiving vessel. When channels on the discharge side are combined, it increases the flow rate. With a special offset pump head, a combination of channels can reduce flow pulsation (Fig. 2). Remember to use larger diameter tubing on the single-channel side of the manifold (either upstream or downstream of the pump) so that you minimize pump cavitation and backpressure.

    Double-Y tubing assemblies using Masterflex® platinum-cured silicone tubing are available for these applications.

  • Type of Fluid

    Fluid considerations are the same for single and multichannel pump applications. Low-viscosity, water-like fluids move easily through many different sizes of tubing. Higher viscosity fluids may require larger diameter tubing and relatively slower pumping speed (rpm). Tubing with a higher ratio of wall thickness to inside diameter (thick-wall tubing) will generate greater suction lift (relative to thin wall tubing of the same ID) and is recommended for more viscous fluids.

Types of Persitaltic Pump Heads


Three types of pump heads adapt easily to multichannel applications: stackable single-channel heads, multichannel heads, and cartridge heads. Multichannel and cartridge heads provide for the maximum number of tubing channels within a relatively small space.

Frequent tubing changes greatly affect pump set-up and maintenance times. Some stackable pump heads must be dismantled or removed from the drive in order to replace the tubing. Other stackable head styles, including the Masterflex® Easy-Load® pumps and most cartridge and multichannel pump heads are easier to set up and service. Operators can remove and replace the tubing without dismantling the pump head.

  • Stackable Single-Channel Pump Heads

    You can add or remove stackable single-channel heads as needed for different applications. Stackable pump heads are therefore popular for applications that require the flexibility to frequently reconfigure the pump design. Stackable heads are preferred for larger tubing sizes, and when the application involves high suction lift and/or discharge pressure.

    Two or four stacked heads can typically be mounted on a drive depending on the driveÕs speed range and horsepower. The dual channel Masterflex® L/S® Easy-Load® II pump head can give you up to 8 channels with four heads stacked on a single drive (Fig. 3).

    You can mount individual pump heads with others of the same type or with pump heads that accept a different range of tubing sizes. This is a valuable benefit for proportional flow applications as it allows you to mix and match tubing sizes or pump head styles to get the proportional flow rates required. Proportional flow rates of over 100:1 are possible.

    Stackable pump heads that incorporate an offset roller design limit the torque loading on the drive circuit when two or more pump heads are mounted together. Stacked heads with offset rollers deliver slightly different volumes from channel to channel when used for short dispensing times/low volumes (depending upon the final position of the rollers). This limitation disappears when the pumps are running continuously or with dispense volumes of several hundred milliliters or more.

  • Multichannel Pump Heads

    Multichannel heads are the newest option for multiple channel applications. These pump heads combine many of the best features of both cartridge heads and stacked single-channel heads.

    These heads offer relatively low pulsation flow from two, four, or eight channels with no cartridges. They are also stackable for up to 32 channels depending on tubing size and formulation and drive power. Between-channel flow is synchronous with no adjustment of occlusion. These features give multichannel heads the configuration flexibility of stacked single-channel heads, as well as the synchronous flow and channel capacity of cartridge heads.

    Masterflex® L/S® multichannel pump heads are available for microbore tubing and for Masterflex® L/S® tubing sizes (Fig. 4).

  • Cartridge Pump Heads

    Cartridge pump heads accept a predetermined maximum number of channels—any number of these channels can be used, up to the capability of the head and the drive. Cartridge pump heads are available separately, or integral to the design of the pump. Masterflex® L/S® cartridge heads are of the modular type and can be mounted on most Masterflex® L/S® drives. Up to 12 individual channels mount on a single head with flow rates as low as 0.0005 mL/min per channel.

    Cartridge pumps have long rollers that provide synchronous fluid delivery between the cartridges. These pump heads also have a higher number of rollers than single-channel heads, which results in lower pulsation flow and higher accuracy at low volumes and low flow rates. These pumps are recommended for low volume/low flow rate fluid transfer applications.

    Cartridge heads with adjustable occlusion offer the highest between-channel accuracy of all pump head types. Fine adjustments to the occlusion in individual channels can effectively compensate for any minor variations in tubing dimensions that lead to slight variations in flow.

Pump Head Drive Selection


Select a drive with sufficient torque (and/or horsepower) and speed to meet the flow and pump head requirements. Drives that operate at a lower speed range typically offer greater torque and can drive a higher number of stacked heads and tubing channels.

Fixed-speed drives are fine for basic transfer applications. Different speeds and gear ratios provide a range of torque outputs and different tubing sizes allow for different flow rates.

Variable-speed drives let you adjust the flow rate simultaneously for all channels with the flow rate in the secondary channels proportionate to the first channel. A very wide range of flow rates are possible by adjusting drive speed as well as selecting different sizes of tubing.

Digital drives provide the most accurate and repeatable speed control and therefore the greatest flow rate accuracy. Depending on features and performance level, digital drives also offer display of flow rate, pump speed (rpm), dispense volume, and cumulative volume (total volume dispensed over multiple dispense cycles. Note that flow rate/volume display will typically be for only one channel unless a number of flowmeters have been built into the system.

Fluid Applications


Fixed-speed and fixed-occlusion pumps are popular for their flow rate repeatability, consistent tube loading, and general ease of use. Used with precision extruded tubing, these pumps can deliver fluids with an accuracy of 3 to 5% between channels. This degree of performance is adequate for bulk fluid transfer, heat exchangers, and ink transfer in printing applications to name a few. Complete Masterflex® I/P® fixed-speed pump systems that are washdown-rated for process applications are available in 3-channel and 4-channel configurations (Fig. 5).

Cartridge and multichannel pump heads are popular for accurate sampling, dispensing, and metering of fluids. The synchronous rollers provide coordinated fluid delivery between each channel in the pump head. Multichannel heads deliver between-channel flow accuracies in the range of 1.5 to 2%. With adjustable occlusion, cartridge pump heads can deliver flow accuracies of 1% between channels. Precise dispensing and metering, analytical techniques in research and quality assurance, and environmental sampling and monitoring require this high level of performance and accuracy.

Summary


Peristaltic tubing pumps offer a unique combination of fluid handling characteristics and configuration flexibility for multiple channel applications. A variety of interchangeable tubing sizes, tubing materials, pump heads, and drives allow you to customize your pumping system at the most economical price possible. Multichannel peristaltic pumping systems are being adapted to a wide variety of applications with tremendous savings in time, space, and resources
Written by Phil Nyren, Fluid Handling Product Manager for