Fitting Union

Image provided by Ferris State University

Unions are used to join two lengths of pipe or a pipe and fixture without having to turn or dismantle either run of pipe. A union is similar to a coupling, except it is designed to allow quick and convenient disconnection of pipes for maintenance or fixture replacement. While a coupling would require either solvent welding or being able to rotate all the pipes adjacent as with a threaded coupling, a union provides a simple nut transition, allowing easy release at any time.

Dielectric Unions are used to separate dissimilar metals (such as copper and galvanized steel) to avoid the damaging effects of electrolysis. When two dissimilar metals are placed in an acidic solution (most tap water is mildly acidic), they will form a battery and generate a voltage. If the two metals touch and conduct, the flow of current from one metal to the other will cause a movement of ions from one to the other, dissolving one metal and depositing on the other. A dielectric union breaks the electrical current with a plastic liner between two halves of the union.

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