Pipe joining methods — plain-end cast iron pipes: Which joint is commonly used to join plain (unflanged) ends of cast iron pipes in water-supply systems?

Introduction / Context:
Joining methods for water mains must provide watertightness, allow some misalignment tolerance, and be maintainable. For plain-end cast iron (or ductile iron) pipes, a mechanical sleeve coupling is often preferred where bell-and-spigot or flanges are not available.

Given Data / Assumptions:

• Pipe ends are plain (no flanges, no socket).
• Objective: quick, reliable connection with field assembly.
• Moderate pressure service typical of distribution mains.

Concept / Approach:
The Dresser coupling is a sleeve with followers and gaskets that compress onto the plain pipe ends to form a tight seal. It accommodates small axial movement and angular deflection, facilitating repair and insertion. Socket and spigot joints need a bell end; flanges require factory flanging; expansion joints serve thermal movement but are not the basic plain-end connector.

Step-by-Step Solution:

Verification / Alternative check:
Field practice shows Dresser-type couplings are standard for repairs, tie-ins, and transitions, including across small diameter differences with proper gasket selection.

Why Other Options Are Wrong:
Flanged joints need flanges; socket and spigot require a bell; flexible/expansion joints are specialty fittings, not general plain-end connectors; lead-caulked bell-and-spigot presumes a socket.

Common Pitfalls:
Reusing old gaskets; misalignment beyond coupling capacity; inadequate surface preparation causing leaks.

Final Answer:
Dresser coupling joint