5 Considerations for Selecting Tubing in Fluidic and Pneumatic Systems
In any fluidic or pneumatic system, tubing is the conduit that supports system performance, safety, and longevity. As such, it’s not some interchangeable component, but an essential tool, the size and composition of which matters deeply to the efficiency and safety of your system. The following list of considerations are designed to help you ask the right questions about your system so you can make the right decisions about your tubing.
1. Material Compatibility
At the heart of selecting proper tubing is understanding the demands of your application. In many cases, your application will determine the material needed for your tubing. Medical and food and beverage applications, for example, involve contact with potable water, significantly impacting your tubing options. For these specific examples, look for “medical-grade tubing (USP VI)”, “FDA Approved”, or “NSF Certified”.
The compatibility of the tubing material with the media flowing through it is crucial to avoid potential issues. When referring to a chemical compatibility chart, prioritize materials with an A or B rating as they demonstrate good resistance to solvents, acidic or base chemicals, and other materials. Poor chemical resistance may cause tubing materials to break down, leading to leaching, chemical reactions, and potential failure. Operating pressures and temperatures further compound these issues.
NOTE: Not all compatibility charts use the same rating system. Refer to the chart legend for guidance.
It is always best to start with tubing chemical compatibility or compliance requirements. Luckily, we offer many reference materials to help with this process.
2. Tubing Dimensions
Tubing has two simple dimensions: Outer Diameter (OD) and Inner Diameter (ID). When selecting tubing, both are often provided, but the OD is typically seen as the primary dimension.
OD is particularly important if you’re connecting to Push-In or Compression fittings as this is how these fittings are sized. If you have a ¼" OD tube, then you need a ¼" fitting.
The opposite is true if you use Barbed Fittings. The ID of the tube is what you need to match for the proper sized fitting.
Another important dimension is Wall Thickness. This is the difference between the OD and ID divided by 2. Typically, a thicker wall provides higher pressure capabilities but can impact the flexibility of your tube.
3. Operating Parameters
The operating pressure of a system will matter to the material and wall thickness of your tube. Higher pressures demand a larger wall thickness, a harder durometer, or reinforcement.
Temperature can be a factor, especially as pressures increase. In some cases, tubing subjected to temperatures above 150F will expand, leading to flow rate issues, dislodged fittings, or increased risk of burst.
Lastly, if you have a vacuum application such as a suction cup system, chances are you need a completely different tubing solution compared to simple fluidic applications. Tubing that is too thin or too soft could collapse during a vacuum. Look for reinforced tubing, a bigger wall thickness, or tubing specifically made for vacuum applications.
4. Flexibility & Hardness
The bend radius of tubing provides an idea of at which point the tube is likely to kink, reducing flow. If you have a tight workspace or need to route tubing along a particular path, it helps to plan for the bend radius. One way to address this is by using a different fitting. Instead of using a straight fitting and bending it to an extreme, consider an elbow. If there is movement needed, consider a swivel fitting to help reduce strain on the tube itself. Stresses caused by a severe bend can lead to fitting failure as well, so choose your connection point wisely.
A durometer rating is a comparative value of hardness between various elastomers and plastics. A softer durometer tube will be much more flexible than a harder durometer but may not be able to handle as high a pressure. The durometer will also factor into what fittings you are able to use in your system. Check out our dedicated durometer post.
5. Tubing Connections
Lastly, not all tubing and fitting options are compatible. For instance, higher durometer tubing does not work well with single or multi-barbed hose barbs. For a hose barb to properly seal, and retain under pressure, the tubing needs to stretch over the barb and seal against the fitting. Softer durometers are best for barbed connections. If leaks or retention are a concern due to higher pressures, a clamp offers peace of mind.
Push-in fittings are designed to grab onto harder tubing and often include internal sealing surfaces such as an O-ring. A softer durometer would give too much, impacting the fitting's ability to retain and seal. Because of this, we suggest pairing harder durometers with push-in fittings.
Compression fittings work with a wide range of tubing materials since the mechanical properties of this design capture the tube, delivering both sealing and retention. Ferrules, or tubing inserts, help this fitting work with a wide range of durometers.
Selecting the right tubing for a fluidic or pneumatic system involves considering various factors, such as material compatibility, dimensions, operating parameters, flexibility, hardness, and connections. To narrow your tubing options to those that best meet your needs, start by fully understanding the demands of your application. This will not only help determine the best tubing for your system but also other fittings and flow control choices too.
Our product team and account executives are available to assist you with product selection, identification, and general guidance. Our production team offers tube cutting and tube assembly services to help streamline your processes. Ask our account executives for more details.
