Compression Fittings
What is a compression fitting and how does it work?
A compression fitting connects tubing or pipe without welding or soldering. It typically consists of a fitting body, compression nut, and one or more ferrules. Tightening the nut compresses the ferrule against the tubing and fitting body, creating a mechanical grip and leak-resistant seal. Compression fittings are commonly used in plumbing, instrumentation, and industrial fluid systems.
What is the difference between single-ferrule and double-ferrule compression fittings?
Single-ferrule fittings use one ferrule to grip and seal the tubing.
Double-ferrule fittings use two separate ferrules: a front ferrule primarily responsible for sealing and a back ferrule that grips the tubing. Double-ferrule designs are commonly selected for demanding instrumentation and high-pressure applications, while single-ferrule designs may be suitable for less demanding systems.
Selection depends on the fitting's specifications, tubing material, pressure, and operating conditions.
What is the purpose of a back ferrule in a compression fitting?
The back ferrule grips the tubing and helps maintain a secure connection in double-ferrule compression fittings. As the fitting is tightened, the back ferrule transfers force to the front ferrule while limiting unwanted torque transfer.
This design promotes uniform compression, reliable tubing retention, and resistance to leakage. Back ferrules are particularly important in stainless steel instrumentation fittings and other demanding fluid systems.
Are compression fittings suitable for high-pressure hydraulic applications?
Certain compression fittings are engineered for high-pressure hydraulic and instrumentation systems, but not all compression fittings are suitable for these applications.
Pressure capability depends on fitting design, tubing material, wall thickness, temperature, and installation quality. High-pressure applications may benefit from properly rated double-ferrule fittings. Always verify the manufacturer's published pressure ratings and tubing compatibility before installation.
Why do compression fittings leak, and how can leaks be prevented?
Compression fittings may leak because of improper installation, damaged ferrules, incompatible tubing, contamination, or insufficient or excessive tightening.
To prevent leaks, use properly matched components, inspect tubing surfaces, ensure correct alignment, and follow the manufacturer's installation instructions.
Avoid overtightening, which can deform components and compromise the seal. Replace damaged components rather than attempting to repair them through additional tightening.
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