Skip to main content

Purpose of valves; reflux valve

Short answer

Valves isolate, regulate, prevent backflow, release air, relieve pressure, and drain lines. A reflux (non-return) valve allows one-way flow: a hinged flap opens by forward flow and closes by weight and back pressure when flow stops or reverses, preventing backflow.

What are the purposes of valves in a pipeline? With a neat sketch, describe a reflux valve.

Purposes of valves in a pipeline

Valves are fitted in a pipeline to:

  1. start, stop or isolate the flow (for repair, cleaning, extension of the line),
  2. regulate the discharge and the pressure,
  3. prevent back flow (reflux valve),
  4. release trapped air (air valve) or relieve excess pressure (safety valve),
  5. drain the line (washout or scour valve).

Reflux valve

A reflux valve (also called 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 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 be drained back; at the foot of a suction pipe (foot valve); on rising mains and at service connections to avoid back siphonage.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Water Supply Engineering chapter 9 questions →