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Reflux valve and air relief valve

Short answer

A reflux valve permits flow in one direction only, preventing reverse flow that could damage pumps or cause back-siphoning. An air relief valve automatically vents trapped air at high points to avoid air-lock and admits air when the pipe is emptied to prevent vacuum.

Write about the purposes of reflux valve and air relief valve with necessary sketches.

Reflux valve (non-return valve)

Purpose: to allow flow in one direction only and automatically prevent reverse flow.

  • On the delivery pipe of a pump, so that water does not run back to the pump when it stops, which prevents damage and loss of prime.
  • On pipes leaving a reservoir or tank, and in the house connection to prevent back-siphoning of dirty water.
  flow ->  _____hinge
  =======|\      |=======
         | \ flap|
  =======|__\____|=======
  Flap opens by forward flow, shuts by reverse flow

Air relief valve

Purpose: to release the air trapped at the high points of the pipeline, and to admit air to prevent a vacuum when the pipe is emptied.

  • Air in the line reduces the discharge, causes air-lock, pressure surges and vibration.
       air out
        _|_
       | o | float ball
   ====|___|====  pipe crest

When air collects in the body, the float drops and opens the outlet; once the air has gone, the water lifts the float and closes the outlet.

✓ Answer checked by Claude Opus 5.5 (high effort)

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