Shanghai Jiapeng analyzes the factors affecting the performance of peristaltic pump tubing

The pump tube is one of the important components of a peristaltic pump, and the end user often misplaces the tubing, making it unsuitable for the desired application. Some users even use ordinary pipes instead of peristaltic pump tubes, causing disastrous consequences. With the increasing number of pump tubes on the market, it is also difficult to select pump tubes.

Peristaltic pumps are gaining popularity due to their pollution-free pumping characteristics and the need for less maintenance. However, when designing or purchasing a peristaltic pump system, many engineers often overlook an important component, the pump tube of a peristaltic pump.

Chemical compatibility:

The pipe must be chemically compatible with the fluid to be pumped in order to have good pumping performance and safety performance. With the increasing number of tubing on the market - some peristaltic pump models have up to 15 available tubing - so users can always find a suitable tubing that is chemically compatible with a particular fluid.

Many pump tube suppliers offer chemical compatibility tables. However, engineers should be aware that chemical compatibility tables specific to pump tubing should be used instead of chemical compatibility tables for common tubing. Because ordinary pipes have only general contact with chemicals, and peristaltic pump tubes are in contact with chemical fluids under pressure conditions, the chemical compatibility level of ordinary pipes cannot be equal to the chemical compatibility level of peristaltic pump tubes. Therefore, only the pump tube should be referred to, not the chemical compatibility level of the general pipeline and related materials, otherwise the pump tube will be ineffective or damaged and leaking, resulting in damage or dangerous accident of the pump.

When referring to the chemical compatibility table, the end user should take each component of the solution, not just the main component, for compatibility check with the pipe to be used. Some acids or solvents can cause enough damage to the pump tube even after a few hours or a few days of contact with the pump tube. The end user should check each chemical in the solution to ensure it is compatible with the selected pump tubing.

Also keep in mind that the chemical resistance of the pump tube decreases with increasing temperature. Some chemicals do not affect the pump tube at room temperature, but when the temperature rises to a certain level, it will cause damage to the pump tube. Certain chemical conditions must be specified in the chemical compatibility table, especially temperature limits, to determine chemical compatibility.

If a chemical is not listed in the chemical compatibility table, or if the operating environment conditions of a plant differ too much from those specified in the table, a immersion test can be used to obtain more reliable information. This method can be used if there is no other information to refer to when determining chemical compatibility.

The immersion test procedure is as follows: Take a small pump tube and weigh it, measure the diameter and length. The pump tube was then placed in a closed container containing the relevant chemicals for 48 hours. The tube was taken out, washed and dried, weighed and measured, and the amount of change measured twice before and after was recorded. The pump tubing should also be inspected for signs of softening or embrittlement, which indicate that the chemical has caused damage to the pump tubing. A pumping test can be performed after one or several tubes are preselected. Each candidate pump tube sample should be put into trial operation under the actual environmental conditions of the factory, and the test results should be closely observed. If the pump tube does not show discoloration, swelling, cracking, loss of fluidity, or other signs of deterioration after the test run, it is proven to be compatible with the fluid.

Please keep in mind that in order to select the right pipe, whether it is to check the compatibility table, to do the physical test, or to use the two methods together, the ultimate responsibility should be borne by the end user. Careful analysis and testing can ensure correct test results, thus avoiding pump damage and ensuring personal and property safety.

The chemical compatibility between different pipes and solutions varies greatly. But there are also some materials that are extremely resistant to most chemicals. For example, Viton fluororubber pump tubing is resistant to a wide range of inorganic chemicals and even some organic chemicals. As another example, a polytetrafluoroethylene (PTFE) pump tube is compatible with almost all chemicals. However, the Teflon pump tubing is a rigid tubing that requires a dedicated pump head. In applications where a variety of corrosive chemicals are to be pumped, tubing that is resistant to a wide range of chemicals should be the best choice.

pressure

The advent of high-pressure pump tubing has expanded the range of applications for peristaltic pumps to unprecedented applications, including filtration.

The pressure source of a fluid delivery system can vary. Back pressure is created when pushing fluid through a filter, or pushing fluid through a flow meter or valve, or pumping fluid into a pressurized reaction vessel. Before selecting the pipe, the user should first make sure that all the pressure sources in the system have been clarified and the measured values ​​of the total system pressure have been obtained. When selecting a pump tube for a peristaltic pump, the user should ensure that the pressure in the system does not exceed the recommended working pressure of the pump tube. If the pressure is too high, the pump tube will swell and will not work well with the pump head, resulting in excessive wear and failure. When the system pressure greatly exceeds the bearing capacity of the pump tube, the pump tube may even burst and spray fluid, which may endanger safety. Once a pipe has been selected, use it to ensure that the pressure is maintained within the pressure range recommended by the manufacturer. If the system exceeds the maximum working pressure, a simple pressure relief valve or pressure switch can be installed to prevent accumulation of excess pressure. The function of the pressure relief valve is to vent to the atmosphere when the system pressure exceeds the set value, so that the system pressure drops to a safe level. A more complicated pressure switch can also be used, which will turn off the device or sound the alarm through a relay when the pressure exceeds the set value. Both of the above methods are beneficial for safety when the system pressure exceeds the safety line.

temperature

The operating temperature range of the pump tubing is another important factor to consider. Some pipes, such as silicone rubber, have a wide temperature tolerance range and are suitable for high temperature and low temperature processes. Some pipes such as Tygon® and C-Flex® are suitable for a small temperature range. The end user should first determine the highest and lowest temperatures in the system before selecting the pipe, and then ensure that the selected pump tube is safe to operate in this temperature range. In applications where temperature is to be gradually increased, the end user should consider the effect of temperature on the chemical resistance and pressure capacity of the pump tube. When the temperature is increased, the pressure capacity of the pump tube is reduced.

size

As each roller in the pump head presses through the pump tube, the peristaltic pump pumps a certain amount of fluid, so the size of the pump tube is directly related to the pumping flow, that is, the operation of the fluid delivery system is greatly affected. The pump tube is the key part to consider when designing a high quality peristaltic pump. The optimum size or optimal size range of the pump tubing needs to be calculated. The dimensions here mainly refer to the inner diameter and thickness of the pump tube. The inner diameter determines the amount of fluid pumped per revolution of the rotor, while the thickness determines the ability of the pump tube to return to its original shape after each rolling. This ability greatly affects the service life of the pump tube. The size of the pump tube is too small relative to the size of the pump head, the pump head can not hold the pump tube, the pump tube will be pulled out of the pump head; and the size of the pump tube is too small, the roller in the pump head can not hold the pump tube, This will result in insufficient pumping flow or complete failure. If the pump tube is too large, the excess tubing will wrinkle between the roller and the pump casing or between the roller and the bite bed, resulting in excessive wear and premature failure. When selecting the pump tube size, the end user should follow the manufacturer's recommendations to ensure that the system functions well. In some applications where higher accuracy is required (such as chemical dosing pumps), the size of the pump tubing is even more pronounced. A slight deviation in size will cause the flow or dispensed deviation to be too large to qualify. Although some manufacturers offer pump tubing sizes that are “close” to the recommended sizes and “look the same”, there are often gaps. Therefore, in order to achieve the best performance and working accuracy of the pump system, the user should use the size of the pump tube that is exactly the same size as the manufacturer recommends.

tolerance

The tolerance is the allowable error of the pump tube size. The smaller the tolerance, the smaller the performance deviation of the pump tubing and the better the consistency and repeatability. The greater the tolerance, the more unstable the performance of the pump tubing. Some pump tubing have very small manufacturing tolerances and their dimensional deviations are tightly controlled during extrusion. Pump tubing with smaller manufacturing tolerances is slightly more expensive, but it is worth the cost of pumping performance.

Average life of the pump tube

The conditions faced by peristaltic pumps are relatively harsh, so tubes with better internal quality, especially those with better resilience, will have a longer service life. In the long run, the longer the pipe life, the lower the operating cost. The fewer the number of pump tube replacements, the lower the maintenance costs and downtime. The less likely the pump tube is leaking and bursting. In short, the longer the pump tube life, the lower the total pumping cost. Pump tube manufacturers should provide test data to demonstrate their declared pump life. Some manufacturers have published relevant information in their manuals. In any case, engineers should be aware of the average life of the pipe when designing a system to help the end user develop a preventive maintenance program that can be replaced before the pump tube fails. Pump tubing suppliers with a wealth of technical knowledge can provide users with useful information for specific applications in order to select the right pump tubing material.

transparency

Whether a transparent pipe should be used depends on whether the operator needs to observe the condition of the fluid in the pipe at any time and whether the fluid is sensitive to light. If the operator needs to observe the fluid, bubbles, particles, pollution, etc. in the pipe at any time, use transparent pipes such as Tygon polyethylene or silicone rubber; if the solution is not suitable for exposure, use opaque pipe.

Air permeability

For some gas-sensitive fluids, such as oxidizing fluids, or anaerobic cell culture fluids, users should consider the permeability of the piping. In general, silicone tubing has the highest air permeability. Therefore, for fluids that are not suitable for contact with gases, pipes with lower air permeability should be used.

Regulatory license

For the pharmaceutical industry, regulatory certification is critical. In this industry, every item that comes into contact with the final product must meet specific standards and guidelines. To this end, many pump tubing materials have been developed in strict accordance with regulatory requirements. These regulations include the United States Pharmacopoeia (USP), the European Pharmacopoeia (EP), the US Food and Drug Administration (FDA), the US Department of Agriculture (USDA), and the National Sanitation Foundation (NSF). Of course, it is not enough to only claim that a certain material meets certain regulations. The pump tube manufacturer shall provide the user with a certificate certifying that the pipe complies with the regulations according to the user's requirements. This allows the user to provide the necessary certificates to demonstrate that the pump system complies with the necessary regulatory approvals.

cost

Cost is almost a factor to consider when developing a project plan. As with other components, the user should evaluate the overall cost of the alternative pump tubing. For example, a pump tube costs $2 per foot and needs to be replaced every 500 hours. The other pump tube costs $1 per foot and needs to be replaced every 100 hours; the former is more cost effective than the latter. Sudden rupture of the low quality pump tubing can result in loss of valuable fluid or damage to the pump, resulting in costly downtime and extensive repairs, or even replacement of the entire pump. Therefore, the cheapest pump tube is not necessarily the most economical choice. It would not be possible to pick an ideal pump tube in a wide variety of pump tube markets. However, by carefully studying system requirements, referring to relevant technical specifications, and maintaining close communication with pump tube manufacturers or suppliers with application knowledge and experience, the pump tubing that best fits the relevant pump system can be selected.