Pneumatic fittings
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Frequently asked questions
Which tube dimension sets the push-in fitting size?
Push-in fittings are sized by the tube outside diameter, so 6x4 tube takes a 6 mm fitting. Metric and inch tube do not mix: 1/4 inch tube at 6.35 mm OD will not hold securely in a 6 mm fitting. The other end is chosen by the device port thread.
How do nickel-plated brass and polymer fitting bodies differ?
Polymer bodies are light and cheap, adequate for clean air on general machinery. Nickel-plated brass resists impact, heat and vibration better. Chemical, food or wash-down areas call for 316 stainless bodies.
Do pre-coated fittings need PTFE tape as well?
No. Many taper-thread fittings come with sealant pre-applied, and extra tape can stop the thread engaging fully or crack an aluminium port. Parallel G threads seal on a washer and do not rely on tape.
Why does tube pull out of a push-in fitting?
Common causes are an angled cut, tube not pushed fully to the stop, or tube of the wrong hardness. Use a proper tube cutter for a square cut and pull-test after insertion. Very soft thin-wall PU tube at high pressure also tends to pull out.
How do I remove tube from a push-in fitting correctly?
Press the release collet evenly into the fitting body and then pull the tube out, never yanking the tube before the collet is pressed. Always vent all pressure from the line first. The tube end scored by the gripping teeth should be cut back about 10 mm before reinserting.
Can push-in fittings be used for vacuum?
Most standard push-in fittings are rated for vacuum to around -100 kPa, but check the data for each series. Soft tubing may collapse under deep vacuum, so choose a stiffer grade or a thicker wall. Leakage at the port thread affects vacuum noticeably, so the thread must be well sealed.
How tight should a threaded fitting be in a port?
Tapered R threads seal by wedging, so hand-tight plus about one to two turns with a spanner is enough, and over-tightening easily cracks aluminium or plastic ports. Parallel G threads seal on a gasket or washer at the face, so tighten until the seal is compressed flat. Fitting makers usually publish torque values by thread size.
Should I use straight, elbow or swivel fittings?
Straight fittings have the lowest flow restriction and suit places with enough clearance. A 90 degree elbow is used where tubing must run close to the machine face, and a swivel type lets the tube direction be set after the thread is tightened. For continuously moving mechanisms, a dedicated rotary fitting lasts longer than an ordinary swivel elbow.
