What is a Peristaltic Pump
A peristaltic pump is a positive displacement pump that moves fluid through a flexible tube by mechanically squeezing it, similar to how food moves through the digestive tract (peristalsis).
Core Components
- Flexible tubing
- Pump housing
- Rollers mounted on a rotating rotor
- Drive motor
Principle of Operation (Step-by-Step)
1- Tube Compression
- A roller presses the flexible tube against the pump housing.
- This compression completely closes the tube at that point.
2- Fluid Displacement
- As the roller moves forward, it pushes the trapped fluid ahead of it.
- The volume of fluid moved equals the internal volume of the tube being compressed.
3- Tube Recovery (Suction)
- Once the roller passes, the tube springs back to its original shape.
- This creates a vacuum that draws new fluid into the tube.
4- Continuous Flow
- Multiple rollers ensure there is always at least one compression point.
- This produces a smooth, continuous flow.
Key Operating Characteristics
Positive Displacement
-
- Delivers a known volume per revolution.
- Flow rate is proportional to rotor speed.
No Contact with Pump Parts
-
- Fluid only contacts the inside of the tubing
- Ideal for sterile, corrosive, or abrasive fluids
Self-Priming
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- Can draw fluid without pre-filling the pump
Reversible Flow
-
- Changing motor direction reverses fluid flow
Flow Rate Control
- (Flow rate depends on)
- Tube inner diameter
- Tube wall thickness
- Number of rollers
- Rotor speed (RPM)
Advantages
- Excellent for metering and dosing
- Handles shear-sensitive fluids
- Can run dry without damage
- Simple maintenance (tube replacement only)
Limitations
- Tubing is a wear part
- Pulsation may occur (reduced with more and or offset rollers)
- Limited discharge pressure compared to other pump types
Common Applications
- Chemical dosing
- Medical and laboratory devices
- Food and beverage processing
- Water treatment
- Pharmaceutical manufacturing
Primary Considerations when using a Peristaltic Pump
When using an automatic liquid filler with peristaltic pumps, the primary considerations focus on maintaining filling accuracy, and managing consumable components like tubing.
Fluid Characteristics and Compatibility
Viscosity
Peristaltic pumps are ideal for small volume, non-viscous liquids. For viscous fluids, performance may vary as flow rates often decrease with higher thickness; in these cases, slower RPMs and higher tube wall thickness are recommended to allow the tube time to rebound.
Chemical Compatibility
The liquid only contacts the tubing, making material selection critical. Use specialized compatibility charts for pump tubing.
Contamination Control
These pumps are preferred for pharmaceutical and biotech industries because they offer a clean product path and eliminate metallic contact.
Tubing Selection and Life
Elasticity and Fatigue
The tube is a consumable that suffers from “creep” or fatigue over millions of compressions. For consistent accuracy, use high-elasticity materials like platinum-cured silicone rubber.
Sizing
Correct inner diameter (ID) and wall thickness are essential. If the tube is too large, it may wrinkle and wear prematurely; if too small, the pump head may not grip it properly, leading to failure.
Replacement Schedule
Regular tubing replacement is mandatory to maintain precision, as flow decay occurs over time.
Filling Accuracy and Calibration
Calibration Protocol
Always calibrate using the actual product rather than water, as density and viscosity differences affect fill volume. Check and Recalibrate at periodic intervals to compensate for tubing break-in especially for the first 30 minutes of run time.
Pulsation Effects
The “pulse” created by rollers exiting the pressure area can cause flow variability. Advanced pump designs with multiple offset rollers can reduce and even eliminate these effects.
Nozzle Design
Various nozzle designs are available to increase flow while reducing the potential for dripping. For foaming or splashing, consider “bottom-up filling” where the nozzle rises as the container fills.
Operational Maintenance
Pump Head Care
Periodically wipe the rotor to remove debris. Use only manufacturer-recommended lubricants (typically silicone-based) on the exterior of the tubing to reduce heat and extend life.
Priming
Ensure the system is properly primed to remove air bubbles, which can cause significant filling errors.
Head pressure
High or low head pressure can prevent tubing from rebounding fully, or over inflating as tubing breaks in, significantly reducing accuracy and repeatability.
Peristaltic Pump – Accuracy vs Throughput.
Peristaltic pumps offer many advantages in flexibility when compared with other positive displacement pump methods. By selecting various tubing, you can alter the flowrate of the pump or increase the accuracy. However, the two variables work in opposition to one another, increasing flow rate reduces accuracy while the inverse is also true.
Tubing size is directly related to the pump flow rate and accuracy, impacting the performance of the peristaltic pump. Peristaltic pump design requires specific tubing parameters to function properly. Specific durometer, diameter and wall thickness is required to yield the best performance.
Tubing size refers to the inside diameter and wall thickness of the pump tubing. The inside diameter(ID) determines the amount of fluid pumped per revolution of the pump rotor, while the wall thickness and durometer determines the ability of the pump tube to return to its original shape after each pass of the pressure roller as well as the life of the tubing.
When selecting the appropriate tubing you need to consider the fill volume, desired production rate and required accuracy. These factors trade ML/min for accuracy. The optimal tubing will balance these parameters appropriate for the application.
In some applications that require higher accuracy (such as pharmaceutical), the role of pump tube size is even more prominent. At lower fill volumes(,10ml), maintaining an accuracy of even 1% becomes challenging and required smaller diameter, higher quality tubing.
When pumping faster is actually slower.
Peristaltic pumps function by rotating 2 or more rollers pinching rubber tubing along the circumference of the pump cover. This creates a suction that draws the liquid into and through the pump to the vessel you are filling. As each roller in the pump head passes along the pump tube, the peristaltic pump will pump a certain amount of fluid. The tubing needs time to recover its original shape to provide a cavity to draw in more liquid.
The recovery time of the tubing then becomes a critical factor in the performance and throughput of the pump. This is why tubing durometer and wall thickness are specified by various pump manufacturers; it is a design parameter of the pump. End users should follow the manufacturer’s recommendations when selecting pump tubing sizes to ensure proper system function.
When selecting pump speed, the product being pumped is also a factor. While flow rate does increase with pump speed, it is not linear. As pump speed increases there is less recovery time for the tubing, reducing the cavity volume. The net result is that while faster pump speed increases flowrate, the results are diminishing to a point where there is little to no improvement in flow rate. Add viscosity to the mix and you may actually see flow rate go down at higher speed!
Liquids that are water like, are very forgiving as there is little resistance to flow within the tubing. However, as viscosity increases even mildly, resistance increases and so does the time for the tubing to recover after each pass of the pinch roller.
You will find that there is an optimal pump speed that produces the greatest flow rate per revolution of the pump, with the added benefit of greater tubing life.