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Pipe joints; expansion joint

Short answer

Joints connect pipes and allow for thermal expansion. An expansion joint uses a spigot sliding inside a stuffing box with packing compressed by a gland, allowing the pipe to lengthen or shorten while staying watertight.

Why are pipe joints required? Describe the expansion joint with a neat sketch (how does it work?).

Why joints are required

  1. Pipes are made in limited lengths (3–6 m), so they must be joined to form a long line.
  2. To connect pipes with fittings, valves, pumps and meters, and to change direction or diameter.
  3. To keep the line watertight, allow small movements, and permit repair and replacement.

Expansion joint

An expansion joint lets a pipeline lengthen or shorten with temperature changes without damaging the pipe or leaking. It is used on long, straight, exposed pipelines (such as on bridges) and near valves and pumps.

  pipe ==[ socket | packing | gland ]== pipe
                      ^ bolts
         spigot free to slide in the socket

Working

  • One pipe has a plain spigot end; the next has a special socket (stuffing box) containing a rubber or lead packing.
  • A gland ring pressed by bolts compresses the packing around the spigot, so the joint is watertight.
  • When the temperature rises, the pipe expands and the spigot slides further into the socket; when it falls, it slides out. The packing stays tight in both cases, so the pipe is free from temperature stress.

✓ Answer checked by Claude Opus 5.5 (high effort)

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