| A tubing failure is defined as one of two conditions. 1. The tubing wears out and breaks. It generally splits along the longitudinal axis where the largest amount of stress is being placed on the tubing (see diagram). A piece of tubing has a finite # of times it can be compressed before breaking. This is a function of the tubing material and the wall thickness to inside diameter (I.D.) ratio.  2. A loss of 50% of flow rate The tubing fatigues or loses its ability to snap back to its original shape when it is released from the rollers. The flow rate decreases significantly because the vacuum created behind the roller as the tubing regains its shape decreases with fatigue. Therefore the fluid will not be pulled through the pump head as quickly. Figure A shows a cross sectional area of tubing. Figure B shows the same piece of tubing compressed by the rollers in the pump head and Figure C shows the fatigued tubing. Like #1 above, this is also a function of tubing material and wall thickness to I.D. ratio. 
|  | Keeping these points in mind, here are some ways to increase the life of your tubing: 1. Slow down the drive speed This decreases the frequency that the tubing is being compressed. To maintain the same flow rate, use a larger tubing size. 2. Choose a thick-walled tubing This will increase the number of compressions required to wear the tubing out, and it will increase its memory capacity. e.g. size 25 and size 15 tubing both have the same I.D. and provide the same flow rate, but size 15 has a thicker wall and will last longer. 3. Select the longest life tubing formulation that is compatible with your fluid Norprene® and Pharmed® have the longest lifetimes, C-flex® and silicone have the next longest lifetime, Tygon® formulations have shorter life, and Viton® is generally the shortest lived (less than 250 hours at 100 rpm). 4. Reduce system pressure Tubing lifetime decreases significantly at higher pressures, especially tubing formulations such as C-flex and silicone which have low pressure ratings. 5. Reduce the occlusion This decreases the stress applied to the tubing every time it is compressed. 6. Avoid sharp tubing bends, especially near the pump head. When using Easy-Load® pump heads, run the tubing straight out of the pump head for at least 6-8". This will keep the tubing centered over the rollers. 7. Develop a preventative maintenance program Move the piece of tubing that is over the rollers 6-8" after a set number of hours before it reaches its failure point. Use the published charts in the Cole-Parmer® catalog or the Masterflex reference book to estimate the number of running hours before failure. |