The tube is the last thing people think about on a pneumatic line. It’s also the first thing that fails.
I’ve seen machines stop for a tube that cost less than the coffee on the bench. Kinked, melted, cracked at a fitting. The fix is easy. The pattern is not. Most tubing failures are a material mismatch, not bad luck.
Two materials cover almost every air line: PU and nylon. They look similar in a coil. They behave completely differently in service. Here’s when to use which.
Does the line move?
PU wins anywhere the tube has to flex. Robot arms, moving cylinders, tool drops, anything that bends repeatedly. Polyurethane springs back and shrugs off abrasion.
Nylon is stiffer. It holds pressure better, but bend it tight and it fights back. Run nylon on a moving axis and you’ll chase fatigue cracks for months.
Heat and pressure come next
PU tops out around 60°C and handles roughly 1.0 MPa working pressure. Fine for a normal shop. Wrong near an oven, a motor, or a hot valve bank.
Nylon takes higher temperatures and keeps a bigger safety margin under constant pressure. Hot cabinet, high-pressure circuit, safety-critical air? Step up to nylon.
Colors do real work
Color coding is not decoration. Blue for supply, black for vacuum, red for high pressure or exhaust. When a tech can trace a line by color in three seconds, downtime drops.
Sizes: trust the numbers, not your eyes
Pneumatic tubing is sized by outside diameter. Metric runs 4 mm up to 16 mm OD, plus inch sizes like 1/4 and 3/8. The OD has to match your fitting exactly. A loose tube leaks. An oversized tube cracks the body.
Replacing an old line? Read the numbers printed on it or measure the OD with calipers. Guessing gets you a second trip to the shelf.
Check the cut before blaming the tube
Most “the tube keeps blowing off” calls are bad cuts, not bad material. A diagonal end leaks and works loose inside a push-in fitting. Cut square, push until it bottoms out, give it a tug.
Still unsure? Send us the application, the pressure, and whether the line moves. We’ll name the material, the OD, and the color in one reply. Tube is cheap. Downtime is not.
Browse PU, nylon, and PE tubing at cnruichen.com/air-tubing/ or email [email protected].