Understanding Compression Fittings: A Comprehensive Guide

What Are Compression Fittings?

Compression fittings are mechanical connectors used to join two pipes or tubes together without welding, soldering, or adhesives. They seal by compressing a ferrule (olive) onto the tube as the nut is tightened, creating a secure, leak-resistant connection.

In one sentence

A compression fitting seals when tightening the nut forces the ferrule to “bite” and compress onto the tube and fitting body.

How Do Compression Fittings Work?

Compression fittings create a seal through a straightforward tightening process. As the nut tightens, it pushes the ferrule onto the tube and into the fitting body, forming a mechanical seal.

Insert the pipe or tube: Push the tube into the fitting body until it seats fully.
Position the ferrule (olive): Slide the ferrule over the tube in the correct orientation.
Tighten the nut: Tightening compresses the ferrule, which grips the tube and seals against the body.

Tip

Compression fittings are ideal where you want a strong seal without heat—and where future disconnection may be needed.

Key Components of a Compression Fitting

A typical compression fitting includes three main parts:

Fitting body: The main connector that forms the sealing surfaces.
Compression ring (ferrule / olive): The ring that compresses to grip and seal on the tube.
Compression nut: Tightens onto the body to compress the ferrule.

Benefits of Compression Fittings

Compression fittings are popular because they’re practical, reliable, and easy to service:

Ease of installation: No soldering, welding, or special hot work required.
Serviceable connections: Can be disassembled for maintenance or modifications.
Leak-resistant seal: A correctly fitted ferrule provides a dependable seal.
Versatility: Suitable for many tube materials (commonly copper, brass, steel—some types also suit plastic).
No heat or chemicals: Safer in environments where flames or adhesives are unsuitable.

Common Applications of Compression Fittings

Compression fittings are used across a wide range of systems and industries, including:

Plumbing systems: Water lines, taps, valves, and general pipework connections.
Gas systems: Gas appliance lines where a reliable seal is essential.
Hydraulic systems: Tube connections where serviceability is important and pressures are appropriate.
HVAC / refrigeration: Copper tube connections in HVAC lines and equipment.
Instrumentation: Controlled flow systems for liquids and gases in industrial or lab settings.

How to Install a Compression Fitting: Step-by-Step

Correct installation is key to preventing leaks and avoiding damage. Use this checklist:

Cut the tube cleanly: Make a straight, square cut with a proper cutter where possible.
Deburr the edge: Remove sharp edges so the ferrule seats correctly.
Fit nut and ferrule: Slide the nut on first, then the ferrule (ensure correct orientation).
Seat the tube fully: Push the tube into the fitting body until it bottoms out.
Tighten correctly: Hand-tighten, then tighten with a spanner—avoid overtightening.
Test for leaks: Pressurise the system and check; tighten slightly if needed.

Safety note

Always isolate and depressurise the system before working on fittings—especially on gas or hydraulic lines.

Common Mistakes to Avoid

Overtightening: Can deform the ferrule and damage tube, causing leaks.
Reusing ferrules: Ferrules often deform during installation—replace them if the joint is dismantled.
Incomplete insertion: If the tube isn’t fully seated, the seal may fail.

Maintenance and Longevity

Compression fittings are durable, but periodic checks help prevent failures:

Inspect periodically: Look for weeping, corrosion, and movement or vibration at joints.
Replace worn components: If a fitting leaks after years of service, replace the ferrule (or the full fitting if needed).