By Eric Rentsch, Product Marketing Manager, Fluidics
Problems and solutions to common pump tubing issues
You can take all the necessary precautions and best practices to ensure you are using the appropriate tubing for your peristaltic pump. However, tubing issues, mostly driven by human error, can still occur.
Tubing issues can lead to pump inaccuracies, reduced pressure capabilities, or even loss of product through rupture. Each of these means higher costs for you. One the best practices to prevent tube rupture is to always load a “fresh” length of tubing into your peristaltic pump. When that is not an immediate possibility for you, here are some tips to help you find a quick solution to your tubing problem when things aren’t quite flowing your way.
1. Tube has longitudinal gash or a few external gashes
Your tubing has rotor scoring. Tubing is too far from center and is clamped onto the rotor disc. The pump drive overpowers the additional load from the friction created so the rotor disc will grind the tube. Depending on use, this can present in different way. If the application is long-term use, the tube may eventually rupture, but there will be only one breach in the tube. If the tubing is frequently adjusted there will be multiple gashes—but usually external. In this case the tubing may not rupture from rotor scoring, but the lifetime of the motor and the accuracy of the pump will be affected.
Tip for rotor scoring
Ensure tubing is not loaded onto the rotor disc and is centered for maximum accuracy. Most Masterflex® pump heads have spring-loaded tube guides on either side to assist centering the tubing on the rotor and mitigate tube walking.
2. Tube has many small to medium cracks inside the tubing walls
Your tubing has chemical degradation. The media being pumped is incompatible with the tube formulation. While the chosen tube and media combination may work in simple transfer applications the repeated occlusion or actuation of the tubing inside the pump head exacerbates the degradation inside the tube. This is presented by the internal cracks forming at the rotor strike site.
Tip for chemical degradation
Use tools such as the Cole-Parmer tubing compatibility database to find the right tubing. We recommend that you always test the tubing in the pump under actual temperature, vacuum, and pressure, or other operating conditions before continuous use. You can also call our technical application specialists at 1-800-323-4340.
3. Tube physically transfers along the direction of the pump flow
You are experiencing tube creep. The tube rollers are slightly pushing the tubing along the occlusion bed at every strike. Tube creep is annoying but does not necessarily indicate poor performance. Extra resistance may be in the rollers or a cleaning solvent may have been used on the tubing, causing it to stick. Alternatively, the tubing is no longer being fully occluded and is pushing pushed by the rollers instead of crushed in place.
Tip for tube creep
Use adjustable occlusion pump heads such as the Masterflex® L/S® Easy-Load® Pump Heads for High-Performance Precision Tubing or the Masterflex L/S® Easy-Load® II Pump Head for High-Precision Tubing. The adjustable occlusion will allow you to tighten down the tubing to prevent slipping from happening. The adjustable occlusion will also allow for better performance in pressure and viscosity applications. As a quick fix, zip ties or duct tape wrapped around the tubing at the inlet and outlet will prevent the tube from slipping as well.
4. Tube has become opaque after autoclaving
You are seeing trapped moisture. Due to the increased pressure and temperature, steam can become trapped inside the tube walls. In most cases this is only a visual defect.
Opacity is okay, assuming that this is just the steam absorbed in the tubing which can be common for this material type. The autoclave forces some water into the tubing. Because the tubing is clear and the tubing and water have different refractive indices, the light entering the tubing is scattered, which makes it look opaque.
Tip for trapped moisture
The tubing will dry over time, this can be accelerated using dry oven heat at 40 to 50°C for a few hours. This will help the tubing regain its original clarity.
5. Inaccurate pump volumes; motor RPM needs adjustments
Your tubing is not yet broken in. As the tubing is occluded inside the pump head, the tube structure relaxes slightly over time. This is due to the repeated deformation of the tube and the increase in temperature from the roller friction (as well as thermal increase from the compression). As the structure relaxes, its elastic memory reduces and so it does not snap back into place as readily, thus the fluid packet in each rotor rotation will decrease over time.
Tip for breaking in tubing
Break tubing in by running your pump at max RPM for 10 to 15 minutes prior to start of your application. Alternatively, Masterflex offers a flow controller which works in tandem with the Masterflex pump and an ultrasonic flow sensor to automatically adjust your pump speed for you. Another benefit of using a flow controller is that the pump performs real-time adjustments, resulting in zero time of inaccuracy.
Learn how to eliminate manual pump adjustments as your tubing ages.