How Compression Fittings Work, in Non-Technical Terms

Lead free compression fitting

Fittings are a general class of parts that, quite simply, connect tubular items such as pipes and hoses together. There are many types, but one of the most important to know about — and yet one of the trickiest to understand — is the compression fitting. Here’s a basic explanation, in non-technical terms:

How Compression Fittings Work

Compression fittings are used to fit two thin-walled pipes together. Those pipes may be made of the same material, or they may be made of two different materials, such as copper and PVC (a common combination in basic plumbing, although the applications for compression fittings go far beyond household use).

Compression fittings consist of two main parts: a compression nut that goes on the outside and a ferrule or compression ring that goes on the inside. Ferrules in small compression fittings are usually shaped as rings with beveled edges. When the outer compression nut is tightened, it compresses the ferrule around the pipe. Larger compression fittings generally use a flange with a ring of bolts, instead of a single compression nut, but work in essentially the same way. The resulting seal is highly resistant to leaks, which is why it’s the standard in the chemical, biotech, oil and gas, and semiconductor industries.

Why use a compression fitting, rather than simply soldering the two pipes together? The main reason is that compression fittings can be used to create a reliable connection in spots where soldering would create a fire hazard. Compression fittings can also be installed in tight spaces where soldering would be impossible or impractical.

A Note on Lead Free Compression Fittings

If you’re looking at your options for compression fittings, you’ll find that brass, an alloy of copper and zinc, is the premier choice. (That has to do with its malleability and ductility, its plasticity under both compressive and tensile stress.) But average brass compression fittings may have a small amount of lead added to the alloy. Although the percentage is typically quite low and probably wouldn’t hurt anyone, it’s been mandated that any potable water systems, or systems involving drinking water, use lead free brass fittings — just to be on the safe side. So that’s why you’ll get a choice of either normal or lead free compression fittings.

What’s your interest in compression fittings? Are you planning a project, looking for a distributor, or just curious? Join the discussion in the comments.

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