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Reflux valve with sketch

Short answer

Without a reflux valve, backflow would damage the pump, empty the rising main, cause water hammer, and allow pollution. A reflux (non-return) valve is a cast-iron body with a hinged flap that opens for forward flow and closes automatically when flow reverses, preventing backflow.

Why is a reflux valve necessary? Describe it with a neat sketch.

Why a reflux valve is necessary

Without a reflux valve, water flows back when pumping stops or the pressure fails. This makes the pump run backwards (damage), empties the rising main and loses prime, creates water hammer, and allows polluted water to flow back into the supply. A reflux valve prevents these by closing automatically on reverse flow.

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)

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