Compression fittings are mechanical connectors used to join pipes and tubing without the need for soldering or specialized tools. They consist of a fitting body, a compression nut and a ferrule (also called an olive) that compresses around the pipe to create a watertight seal.

How they work

When assembling a compression fitting, the nut and ferrule slide over the pipe. The pipe is inserted into the fitting body until it seats against a shoulder. As the nut is tightened, it forces the ferrule to grip and compress the pipe. This compression creates friction and deforms the ferrule slightly, forming a seal between the fitting body and the pipe.

Materials

• Brass: Most compression fittings are made from brass and are used with copper or metal tubing.
• Plastic ferrules and inserts: For plastic tubing (such as polyethylene or PEX), a plastic sleeve and a brass insert are used. The insert supports the tubing so the ferrule can compress without collapsing the tube.

Advantages

• No heat required: Compression fittings are ideal where open flame soldering is impractical or prohibited. They are convenient for repairs or retrofits.
• Reusable bodies: The fitting body can often be reused if the ferrule and nut are replaced.
• Quick assembly: Requires only basic tools (wrenches) and minimal training. Connections can be made in tight spaces.
• Versatility: Available in various sizes (e.g., 1/4 in., 3/8 in., 1/2 in.) and configurations (straight, elbow, tee) to connect copper, CPVC and some plastic tubing.

Considerations

• Proper alignment: Pipes must be cut square and fully inserted into the fitting. Misalignment can cause leaks.
• Avoid over‑tightening: Tighten the nut only enough to stop leaks. Excess force can deform the ferrule and cause leaks or damage.
• Not for vibrating systems: Compression fittings are less suitable for areas subject to vibration or movement, as repeated movement can loosen the seal.

Installation tips

1. Cut the tubing cleanly and square using a pipe cutter. Remove any burrs.
2. Slide the compression nut and then the ferrule onto the pipe. For plastic tubing, insert the stiffener into the tube.
3. Push the pipe fully into the fitting body until it seats.
4. Hand‑tighten the nut, then use a wrench to tighten an additional one half turn. Avoid using PTFE tape or pipe compound on the threads; the seal forms on the ferrule.
5. Turn on water and check for leaks. If a leak persists, tighten the nut slightly more.
6. If disassembling, replace the ferrule with a new one; reused ferrules may not seal properly.

Compression fittings provide a convenient, solder‑free option for connecting plumbing lines, making them popular for do‑it‑yourself projects and professional installations alike.