Gaining the Swagelok tube fitting advantage
by Jeff Hopkins, on 10/2/12 5:00 AM
Swagelok gaugeable tube fittings and adapter fittings feature a strong grip with no torque, which produces a seal that stands up to hard use. [Updated Jan 2020.]
Tip: Download 34 Swagelok tube fitting performance product test reports, and info specific to several industries.
The two-ferrule mechanical-grip tube fitting
Sometimes you hear a term so often you forget about the meaning behind it. Take the term "tube fitting", for instance. Tube fitting is a general term used to describe categories of components whose purpose is to create a leak-tight connection between a piece of tubing to one or more additional pieces of tubing or other end connections in a fluid system.
The famous Swagelok two ferrule mechanical-grip tube fitting was introduced 65 years ago, and has been the standard ever since.
Wanted: 100% leak-proof fitting connection
System leakage most often occurs at the connections in a system, where fittings under stress can fail. Reliable fittings, then, are crucial. We do acknowledge there is no such thing as a fitting connection that is 100 percent leak-proof under every possible condition. But some designs are inherently better than others. Simple compression fittings, for instance, can't handle much pressure or vibration. Flare fittings can handle higher pressures, but require special flaring tools to prepare the tube.
With these limitations in mind, Swagelok developed the two ferrule mechanical grip fitting in 1947. Swagelok's patented back-ferrule geometry creates a fitting that performs remarkably well in three key areas:
- Tube grip for pressure containment
- Gas seal for leak tight performance
- Vibration resistance for protection from outside forces
Our illustration depicts a cross-section of the fitting in action. As the fitting nut is tightened, it drives the back ferrule into the front ferrule. Notice the "hinge" in the back ferrule. When the back ferrule is driven forward, it grips the tubing and the hinging action creates a large "colleting" region. The colleting region provides improved support to the tube behind the point of grip which protects the swaged area of the tube more effectively from system vibration and fatigue.
The back ferrule is specially hardened in a way that keeps the steel ductile and provides excellent corrosion resistance. Our illustration below portrays the action of the front ferrule. As it moves forward, it polishes the tube and the fitting body bevel which produces a leak-tight gas seal.
The big three
This video clip focuses on the importance of tube grip, gas seal, and vibration protection in tube fitting performance:
When are leaky fittings an option?
Never. A leaky fitting can be expensive and dangerous. In addition to wasting energy, they can hurt product quality and even cause injury. Fixing a leak means unwanted downtime and labor expense. As with many plant operations, prevention is the safest and most economical approach. So start by having the right fittings for the job, using a design that you can rely on.
Our engineers can check your compressed gas system and spot the leaks. We find leaks as small as 1 x10-3 cm3/s, tag and catalog them, and present you with a detailed report designed to help you act.
See how others use Swagelok in dozens of videos and written stories.
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