--- title: "Why Air Tubing Kinks and How to Stop It" canonical: "https://yuannaitube.com/air-tubing-kinking/" language: "en-US" --- RESOURCES # Why Air Tubing Kinks and How to Stop It By [YUANNAI TUBE]() Published 2026-11-09Updated 2026-11-09 ![Blue polyurethane tubing in a wide loop with one kinked section]() **Air tubing kinks when it is bent tighter than its minimum bend radius, bent right next to a fitting, twisted, or asked to move when it was installed as fixed piping.** A kink flattens the bore, cuts flow and weakens the wall. This guide explains each cause and shows, from our own model tables, how the **wall thickness** and outside diameter set the radius a tube can take. **Quick answer.** Keep every bend at or above the tube’s listed minimum radius, including the bend next to the fitting; avoid twisting and pulling; use **coiled tubing** where the line moves; and replace a tube that has kinked, twisted or been crushed. In our **PU tubing** the minimum radius is 2.5 times the outside diameter on models 0425, 0640, 0850 and 1065, and it rises when the wall gets thinner. ## Why tubing kinks - **The radius is too small.** SMC’s precautions state that if the bending radius is less than the minimum value, the fitting may be damaged, or the tubing may crack or be crushed. - **The bend is at the fitting.** The same document says the **bend radius** in the vicinity of the fitting should be at least the minimum bending radius of the tubing. A tube that leaves a fitting at a sharp angle is the most common place for a kink to start. - **The tube is twisted or pulled.** SMC warns against twisting, pulling, moment loads, vibration and impact on fittings or tubing, which can crush, burst or release the tube. - **The tube moves, but was installed as fixed piping.** SMC states that tubing other than **coiled tubing** requires stationary installation. Where the line has to move, use **coiled tubing** or follow the maker’s moving-use guidance. - **The tube is too short.** Tubing changes length under pressure, so a line pulled tight can be forced into a bend when it is pressurized. SMC asks for a sufficient length margin for this. ## How the radius is set: wall thickness and diameter The minimum **bend radius** in a data sheet is a tested value, and it depends on the outside diameter, the wall and the material. In our PU model table the radius follows a clear pattern. For the same 8 mm outside diameter, a thinner wall needs a larger radius: | YN-PU model | Outside × inside diameter | Wall | Min. bend radius | | --- | --- | --- | --- | | 0850 | 8 × 5 mm | 1.5 mm | 20 mm | | 0855 | 8 × 5.5 mm | 1.25 mm | 22 mm | | 0860 | 8 × 6 mm | 1.0 mm | 25 mm | | 1065 | 10 × 6.5 mm | 1.75 mm | 25 mm | | 1080 | 10 × 8 mm | 1.0 mm | 30 mm | The same holds for PE: the 8 × 5, 8 × 5.5 and 8 × 6 tubes are listed at 40, 45 and 50 mm. If a route is tight, choose the heavier wall for the same outside diameter, or a smaller outside diameter, rather than forcing a thin-wall tube around a corner. The full radius table by size and material is in [pneumatic tubing bend radius]() , and the two materials are compared size by size in [PU vs PE tubing]() . ## How to stop kinks 1. **Check the radius at design time.** Take the minimum **bend radius** for your model from the data sheet and check it against the routing, especially at fittings. 2. **Leave a straight run at each fitting.** Let the tube leave the fitting straight for a short length before it bends. Use an angled (elbow) fitting where the tube must turn at once. 3. **Support the line.** Clip or clamp the tube so that its weight does not pull it into a bend. Do not let it hang from a fitting. 4. **Allow length.** Cut the tube a little long so that pressure changes do not pull it tight (see [how to cut plastic tubing]() ). 5. **Do not twist the tube.** Push it straight into the fitting and release any twist along the run before you pressurize. 6. **Use the right construction for moving parts.** For moving equipment see the [coiled air tubing guide]() . 7. **Replace damaged tube.** SMC’s maintenance list includes twisting or crushing of the tubing as a reason to replace it. A kinked tube that has whitened or creased should not be put back in service. ## Is some tubing kink-resistant? Some manufacturers sell **polyurethane tubing** described as highly flexible and kink resistant; Festo’s PUN tubing is an example. That describes how well a tube tolerates bending, not an exemption from the minimum radius in the data sheet. Compare the radius figure for the exact model, as in the table above. ## Air tubing kinking FAQ Why does my air tubing keep kinking? The usual causes are a bend tighter than the minimum radius, a sharp bend at the fitting, twisting, or a fixed-piping tube that is being moved. Check the radius for your model first. How do I keep tubing from kinking? Keep bends at or above the listed minimum radius, leave a straight run at the fitting, support the line and leave enough length so it is not pulled tight. Does a thinner wall kink more easily? In our PU and PE model tables, for the same outside diameter, the thinner-wall tube has the larger minimum **bend radius**. For example the 8 × 6 PU tube is listed at 25 mm and the 8 × 5 at 20 mm. Can I straighten a kinked tube? A kinked section is deformed and weakened. SMC lists twisting or crushing of tubing as a reason to replace it, so cut out the damaged length or replace the tube. What can I use instead of straight tubing for moving parts? **Coiled tubing** is made for lines that extend and retract. See the [coiled air tubing guide]() . ## Sources and scope - [SMC, fittings and tubing precautions (bending radius near fittings, stationary installation, replacement)]() - [PU Tubing — English data sheet (v3-20261020)]() - [PE Tubing — English data sheet (v1-20261021)]() The radius figures are from the YUANNAI TUBE YN-PU and YN-PE model tables and apply to those models only. The routing suggestions are general practice. Confirm the minimum **bend radius** for your exact model before you route a line. Content review: [zhangkexin]() · Marketing Review scope: market information and document references. ## Tell us what your application needs. Send your dimensions, operating conditions and quantity. Let’s identify the right tubing for your project. 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