Flanged joint and reflux valve

Flanged joint

A flanged joint connects two pipes (or a pipe and a valve, pump or fitting) using flanges, which are circular plates fixed to the pipe ends by casting, welding or screwing. A gasket of rubber, rubber-fabric or lead is placed between the flange faces, and the flanges are bolted together, tightening the nuts evenly in turn (diagonally opposite bolts one after another).

             bolt + nut
          ___  |  ___
         |   |=+=|   |
  =======|   | | |   |=======
   pipe  | F |g| | F |  pipe
  =======|   | | |   |=======
         |___|=+=|___|
               |
            bolt + nut
     F = flange,  g = gasket

• Used for valves, pumps, meters and exposed pipes, and in pump houses and treatment plants.
• Strong, watertight and easy to dismantle; but costly, and being rigid it cannot take bending or misalignment.

Reflux valve

A reflux valve (also called a non-return or check valve) allows water to flow in one direction only and closes automatically when the flow tries to reverse.

   flow ->   _______hinge
   =========|\       |=========
            | \ flap |   (flap lifts for
   =========|__\_____|=========  forward flow,
        valve seat           falls shut on reversal)

• Construction: a cast-iron body with a flap (door or disc) hinged at the top, which rests on a seat. Forward flow pushes the flap open; when the flow stops or reverses, the weight of the flap and the back pressure press it onto the seat.
• Uses: on the delivery side of a pump, to prevent back flow when the pump stops and to protect the pump from water hammer; on pipes from a reservoir that must not drain back; at the foot of a suction pipe (foot valve); and on rising mains and service connections to prevent back siphonage.