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Purpose of valves; cutoff valve

Short answer

Valves isolate, regulate flow, prevent backflow, release air, relieve pressure, and drain lines. A cutoff (gate) valve fully opens or closes the line using a wedge gate moved by a screw spindle; it is not for throttling, and gives low head loss when open.

What are the purposes of valves in pipelines? Describe the working and function of the cutoff valve with a neat sketch.

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).

Cutoff valve (sluice valve)

A cutoff valve (sluice or gate valve) is used to stop or allow the flow completely; it is not used for throttling.

      wheel / spindle
          |
       __ | __
      |  [|]  |   <- gate (wedge) moves up and down
  ====|  | |  |====
      |__|_|__|
         body
  • Construction: a cast-iron body with a wedge-shaped gate (disc) moving across the flow by a screw spindle turned with a hand wheel.
  • Working: when the wheel is turned, the gate rises (valve open: full bore, little head loss) or goes down across the pipe (valve closed: tight shut-off).
  • Uses: at the beginning of branches, at intervals on the main lines (sectional valves), before and after pumps and meters.

✓ Answer checked by Claude Opus 5.5 (high effort)

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