Pipe joints; socket and spigot joint

Why pipe joints are required

Pipes are made in short lengths (3–6 m), so joints are needed to connect them into a long line, to join fittings and valves, to change direction, and to keep the line watertight while permitting repair or replacement.

Socket and spigot (bell and spigot) joint

This is the common joint for cast iron (CI) and ductile iron (DI) pipes. One end of each pipe is a socket (bell) with an enlarged inner diameter, and the other end is a plain spigot.

     socket (bell)            spigot
   __________________    ___________
  /  ______ lead ___ \  /          \
 |  | yarn   |lead |  |<----spigot enters
  \__|_______|_____|__/
        gap about 10 mm

Making the joint

1. The spigot of one pipe is inserted into the socket of the previous pipe and centred, leaving an annular gap of about 10 mm. Pipes are laid with the sockets facing uphill.
2. The gap is filled to about half its depth with spun yarn (hemp) or gasket, rammed (caulked) tightly.
3. The rest is filled with molten lead poured at once and caulked, or with a cement mortar (1 : 1) in some cases. A rubber ring can also be used (push-on joint).

Features

• Merits: easy and quick to make, flexible to a few degrees of deflection, and it takes a small settlement.
• Demerits: it cannot resist the longitudinal (pull-out) thrust, so thrust blocks are needed at bends and dead ends under high pressure; skilled labour is needed for lead jointing; lead is costly; and the joint is difficult to dismantle.