Using the correct tubing is critical for the safe and proper use of peristaltic pump systems. When working with this type of pump system, the tubing needs to match the application and the pump. Too often, end users unknowingly select a tubing formulation unsuitable for their applications. Some even substitute general-purpose transfer tubing for tubing specifically designed for peristaltic pumps. Testing and then using the correct tubing in a peristaltic pump system can prevent hazardous situations such as harmful chemical leakage or tubing rupture.
With so many tubing types available, one type of tubing does not fit all applications. To select tubing that can help with safer pumping, the following factors should be considered: chemical compatibility, pressure, temperature, tubing size and life expectancy.
Tubing and chemical compatibility
The tubing material and the pumped fluid must be compatible. Many tubing suppliers provide chemical compatibility charts. However, it is important to use a chart designed specific to pump tubing instead of a chart that covers tubes intended for general use. Tubing that gets an acceptable rating for general contact with a given chemical may not withstand exposure to the same chemical when subjected to the physical stresses of peristaltic pumping. Failure to do so could result in tube failure and leakage, which could create a hazardous situation.
When using chemical compatibility charts as a guide, check each constituent of the solution, not just the main ingredient, against the material to be used. Even trace levels of some acids or solvents can be enough to destroy pump tubing when the tubing is exposed to the materials over hours or days.
It is also important to remember that chemical resistance decreases as temperature increases. Chemicals that have no effect on the tubing at room temperature could attack the tubing at elevated temperatures. The chemical compatibility chart must indicate which conditions, particularly temperature, were used to determine compatibility.
If a chemical is not listed on the compatibility chart, or if a plant’s operating conditions are significantly different from those used to determine the chemical resistance ratings, an immersion test can provide more useful information. This method can help determine chemical compatibility when no other information exists.
In an immersion test, a small piece of tubing is weighed, and its diameter and length are measured. The tubing then is immersed in a closed vessel with the chemical in question for a minimum of 48 hours. Afterward, the test piece of tubing is rinsed, dried, weighed and measured, and any changes are recorded. The tubing should also be examined for signs of softening or embrittlement, which indicate the chemical has attacked the tubing. However, be warned that even if tubing passes the immersion test, variations in temperature, pressure or concentration may cause tubing failure. Serious injury may result. Use suitable guards and/or personal protection when pumping chemicals.
Once a promising material or group of materials is identified, a pump test should be performed. A sample of each potential tubing in a pump should be run under a plant’s actual process conditions and the results carefully monitored. If the tubing survives the test without discoloration, swelling, cracking, loss of flow or other signs of deterioration, it is compatible with the fluid.
Whether suitability is determined using a chart, a physical test or a combination of the two, the final responsibility lies with the end user. Careful analysis and testing are best practices to help prevent pump damage and protect personnel and the facility.
The importance of pressure
When selecting a tubing material for use in a peristaltic pump, ensure 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 and result in an improper fit through the pump head, which causes excessive wear and tubing failure. If the system pressure greatly exceeds what the tubing could handle, the tubing could even burst and spray fluid, creating a safety hazard.
Pressure sources in a fluid handling system can vary. Backpressure can be generated by the fluid passing through a filter, by the fluid pushing through flowmeters or valves, or by the fluid pumping into pressurized reaction vessels. Before selecting a tubing material, be sure to identify all pressure sources in the system and have an accurate reading of the total system pressure.
Once a tubing material is selected, it is important the application remain within the manufacturer’s pressure recommendations. If the system may exceed the maximum working pressure, a simple pressure-relief valve or pressure switch can be installed to prevent excessive pressure buildup. A pressure-relief valve will vent to the atmosphere when the system pressure exceeds the setpoint, allowing the system pressure to drop back down to a safer level. A more sophisticated pressure switch uses an electrical relay to shut down equipment or sound an alarm when the system pressure exceeds the setpoint. Either method is a good safety precaution when system pressure could reach excessive levels.
Working temperature of tubing material
The working temperature range of a tubing material is another important consideration. Some materials such as silicone have a relatively broad temperature range and are well-suited to high- and low-temperature processes, whereas others are designed for use within a narrower temperature range. Before selecting a material, identify the minimum and maximum temperatures possible in the system, then ensure the tubing can operate safely within that range.
If a process will operate at elevated temperatures, consider the effect of temperature on chemical resistance and pressure capabilities. As temperature increases, the chemical resistance and working pressure for a given tube decreases.
Tubing size must fit the pump head
For safe pumping, always use the exact tubing size recommended for the pump. Because peristaltic pumps deliver fixed amounts of fluid with each pass of a roller over the tube, the size of the tube has a direct effect on the amount of fluid delivered. Thus, tubing dimensions (inner diameter, outer diameter, wall thickness) have a great impact on fluid handling system operation. Even a few thousands out-of-tolerance dimensions can have an impact on operational satisfaction and safety.
If the pump tubing is too small for the pump head, the pump head may not retain the tubing properly, and the tubing could be pulled through the pump head. The pump’s rollers also may not compress undersized tubing properly, leading to insufficient flow or even complete failure.
On the other hand, if the pump tubing is too large, the excess material can become pinched between the rollers and the pump head housing or occlusion bed, causing excessive wear and premature failure. When choosing a tubing size, end users should always follow the pump manufacturer’s size recommendations to ensure safe performance from the pump system.
Tubing life expectancy
Keep pump operators safe with preventive maintenance. Knowledge of the average tubing life will help to develop a preventive maintenance plan to ensure tubing is replaced before it fails. Pump tubing manufacturers should be able to supply test data to support their tubing life claims. A pump tubing supplier with extensive technical expertise can help make a well-informed decision about the right tubing material for an application.
With the numerous pump tubing choices available, finding the ideal tubing takes time. However, by carefully identifying the system requirements, using the available tubing technical data and working with a tubing manufacturer or supplier with specific application knowledge and experience, end users can identify the best tubing to help increase the safety of peristaltic pump systems.
Gregg Johnson is global senior product manager for Cole-Parmer’s Masterflex and Ismatec brands. He has worked in the pump industry for more than 30 years and specifically with peristaltic pumps for more than 19 years. Visit coleparmer.com for more information.