Peristaltic Pump Tubing and Chemical Compatibility
Tubing is an essential part of any peristaltic pump. But users often choose unsuitable tubing for their applications because they fail to consider the compatibility between the tubing and the chemicals that will be pumped through it.
Choosing the wrong tubing can lead to several problems, including inaccurate results, tubing degradation, or damage to your pump. That is why it is vital to choose the tubing that is best suited to the specific conditions or your applications.
The following are some factors when selecting tubing for your peristaltic pump. You can click on each topic to go directly to that section.
- The importance of chemical compatibility of peristaltic pump tubing
- Additional peristaltic pump tubing parameters to consider
- Finding the proper tubing for your needs
The importance of chemical compatibility for peristaltic pump tubing
Compatibility between peristaltic pump tubing and the chemicals or fluids pumped through it is essential if you want to achieve the levels of performance and safety, you need in your lab. With so many tubing materials available, you can find compatible tubing for nearly any chemical or fluid.
While many suppliers provide chemical compatibility charts or databases for general-use tubing, engineers and technicians should use charts specifically designed for peristaltic pump tubing instead. That is because general-use tubing rated as suitable for any purpose with a given chemical might not withstand exposure to the same chemical when subjected to the physical stresses of peristaltic pumping. That could lead to tubing failure or leakage that damages pumps or creates a hazardous situation. Avantor’s tubing compatibility database allows you to select the chemical you will use to generate a list of compatible tubing choices.
When using chemical compatibility charts to evaluate tubing, check compatibility with each component of the solution, not just the main ingredient. Even trace levels of some acids or solvents, for example, can be enough to destroy pump tubing when the tubing is exposed to that solution for hours or days.
It is also important to remember that chemical resistance can decrease as operating temperatures increase. Chemicals that do not affect the tubing at room temperature could attack the tubing at elevated temperatures. Chemical compatibility charts should indicate the conditions, particularly temperature, used to determine compatibility.
Chemical compatibility charts typically rate tubing as follows:
- Excellent: Tubing should experience no chemical degradation
- Good: Tubing will likely experience some degradation
- Fair: Tubing may experience significant degradation
- Poor: Material is not recommended for applications
Immersion tests can help determine chemical compatibility
Immersion testing can provide helpful information if the chemicals you use are not listed on a compatibility chart or if the operating conditions at your facility are significantly different from those used to determine chemical-resistance ratings.
To conduct an immersion test, start by weighing a small piece of tubing is weighed, then measure its diameter and length. Then place the tubing in a closed vessel filled with the chemical you will use. Leave the tubing immersed in the sample for at least 48 hours.
Remove the tubing from the solution, rinse it, and let it dry. Weigh and measure the tubing and compare the results to your original measurements. You should also examine the tubing for signs of softening or embrittlement. Both indicate that the chemical you used has attacked the tubing.
After identifying potential tubing options, you should conduct pump tests to make your final choice. Install samples of each tubing in a pump and run it under your actual process conditions while you carefully monitor the results. If the tubing sample survives the test without discoloration, swelling, cracking, loss of flow, or other signs of deterioration, then it is compatible with the fluids and chemicals you use.
Whether you determine compatibility using a chart, a physical test, or a combination, keep in mind that careful analysis and testing will help ensure the best choice.
Additional peristaltic pump tubing parameters to consider
Peristaltic pumps provide contamination-free pumping and relatively low maintenance. However, engineers and technicians may overlook several important factors when they choose peristaltic pump tubing. The following are factors you should consider in addition to chemical compatibility.
Peristaltic Pump Pressure
Peristaltic pump applications typically have been limited by the pressure capabilities of the tubing. In the past, peristaltic pump tubing typically had working pressure ratings ranging from about 10 pounds per square inch (psi) to 40 psi. Softer materials, such as silicone, fell, at the low end of the range, while firmer materials, such as Norprene®, were at the higher end.
Advances in tubing formulation and technology have produced high-pressure materials that have expanded the working pressure range to as high as 125 psi. As new materials are developed, peristaltic pumps should be suitable for more high-pressure applications.
There are several sources of pressure in a fluid-handling system. For example, pressure may be generated as fluids pass through a filter, as they are pumped through flowmeters or valves, or by fluids pumping into pressurized reaction vessels. Before you choose tubing materials, be sure you have identified all pressure sources in your system and have an accurate reading of the total system pressure.
When you select tubing to use in a peristaltic pump, be sure the pressure in the system does not exceed the recommended working pressure of the tubing. If the pressure is too high, the tubing could swell, resulting in an improper fit through the pump head. That could cause excessive wear and tubing failure. If system pressure greatly exceeds what the tubing can handle, the tubing could even burst and spray fluid, creating a safety hazard.
It is important that applications remain within the manufacturer's pressure recommendations. If your system could exceed the maximum working pressure, you can install a simple pressure-relief valve or pressure switch to prevent excessive buildup. Pressure-relief valves vent the system to reduce pressure to a safe level. Pressure switches use an electrical relay to shut down equipment or sound an alarm when the system pressure exceeds a setpoint. Either method is a good safety precaution if system pressure could reach excessive levels.
Temperature
Be sure to consider the working temperature range of the tubing. Some materials, such as silicone, have a relatively broad temperature range and are well-suited to both high- and low-temperature processes. Other materials, such as Tygon® or C-Flex®, are designed for a narrower temperature range. Before selecting a material, you should identify the minimum and maximum temperatures possible in your system to be sure the tubing can operate safely within that range.
If a process will operate at elevated temperatures, you should consider the effect of temperature on the chemical resistance and pressure capabilities of your tubing. As temperature increases, the working pressure for a given tube may decrease.
Pump dimensions
Peristaltic pumps use rollers to compress and decompress tubing and move fluids through the system. That means the size of the tube can have a direct effect on the amount of fluid delivered.
Well-designed pumps are engineered to work with an optimum tubing size or range of tubing sizes, considering the tube's inside diameter and wall thickness. The inside diameter determines the amount of fluid delivered with each pumping cycle. The wall thickness affects the tubing's ability to spring back to its original shape after each compression. That can have a significant effect on the overall life of the tubing.
If the pump tubing is too small for the pump head, the pump head might not hold the tubing properly, and it could be pulled through the pump head. The pump's rollers might not be able to compress undersized tubing properly, leading to insufficient flow or complete failure.
On the other hand, if the pump tubing is too large, excess material could be pinched between the rollers and the pump head housing or occlusion bed. That could cause excessive wear and premature failure. When you choose a tubing size, follow the pump manufacturer's recommendations to ensure good performance.
Although some manufacturers provide tubing for use in peristaltic pumps with dimensions close to the pump manufacturer's recommended sizes, being close may not be adequate. The more important accuracy is in a process—as in chemical metering, for example—the more significant tubing dimensions become. Even small variations in tubing size can cause unacceptable deviations in flow rates or the amount of fluid dispensed. For optimal performance and accuracy, you should always use the exact tubing size recommended for the pump.
Tolerance
Tolerance is a measure of how much variation exists in tubing dimensions. The lower the dimensional tolerances, the less variation there is in pump tubing. Less variation means better consistency and repeatability.
Larger tolerances mean there are more significant variances in tubing dimensions. That can lead to unpredictable results or results that cannot be consistently replicated. Although close-tolerance tubing usually costs more than general-purpose tubing, the improved pumping performance is worth the extra expenditure.
Tubing life expectancy
Tubing made from some materials can better withstand the rigors of peristaltic pumping and can last longer than tubing made from less resilient materials. Longer-life tubing may be more expensive upfront but more economical in the long run because it needs replacement less frequently and reduces downtime and the cost of maintenance.
Pump tubing manufacturers often supply test data that shows the expected life of their tubing. It is important that engineers know the expected life for tubing and other materials so they can effectively design systems. Knowing the average life of tubing will also let engineers develop preventive maintenance plans that schedule tubing replacement before it fails. You can find life expectancy information in references such as Masterflex® literature.
Transparency
Transparency may be an important consideration when you choose tubing, depending on your pump application. Transparent tubing—such as Tygon or silicone—may be the best choice if lab workers must be able to monitor fluid flow or quickly check for air bubbles, particulates, contaminants, or other irregularities.
In other situations, such as light-sensitive fluids, tubing made from an opaque material would be a better option, such as Pharmed BPT.
Gas Permeability
You should be sure to consider a tubing’s permeability if you are using gas-sensitive fluids, such as solutions that must be protected from oxidation, or if you are using anaerobic cell cultures. Silicone tubing is generally among the most gas-permeable materials, while tubing made from thermoplastic materials tends to be relatively impermeable. The less permeable the material, the more your tubing will help prevent the problems that can occur by exposing fluids to air.
Regulatory Approval
Regulatory approval is essential in many applications and particularly in the pharmaceutical industry. Everything that comes in contact with the final product in pharmaceutical production must meet specific standards and guidelines. Many tubing materials are designed to meet various regulatory approvals, including those issued by the United States Pharmacopoeia (USP), European Pharmacopoeia (EP), U.S. Department of Agriculture (USDA), and National Sanitation Foundation (NSF).
The tubing manufacturer should be able to provide you with a certificate that confirms the tubing they produce meets the appropriate regulations for your use. That will help ensure that you can provide the requisite documentation to certify that your system complies with all applicable regulations.
Cost
When you are selecting which tubing to purchase, be sure to consider overall operational costs fover the long term. There is more to the cost of tubing than the initial purchase price. For example, tubing that costs $2.00 per foot and must be replaced every 500 hours is more cost-effective than tubing that costs only $1.00 per foot but requires replacement every 100 hours.
In addition, if poor-quality tubing ruptures, it could waste valuable fluids or cause extensive damage to your pump. That could mean costly downtime and expensive repairs or replacement for your pump.
With so many choices in pump tubing, finding the ideal tubing for an application might seem to be a daunting task. By carefully identifying your system requirements, using available tubing technical data, and working with tubing manufacturers or suppliers, you can identify the best tubing for your pump systems.
Finding the proper tubing for your needs
Masterflex® can help you meet your tubing needs. We can help you accurately size tubing for your pumpheads and advise you regarding hardness, material, transparency, and cost to choose the best tubing that best meets your needs.