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Pressure relief valves

Short answer

Pressure relief valves protect pipelines from water hammer and excessive pressure by automatically opening at a set limit to discharge water. A spring-loaded valve lifts off its seat when pressure exceeds the setting, then closes when pressure drops, preventing bursts.

Why are pressure relief valves necessary? Describe with a neat sketch.

Why pressure relief valves are necessary

Sudden closure of valves, the stopping or starting of pumps, or any rapid change in flow produces water hammer (a high-pressure wave), and pressure can also become too high in low-lying parts or in pumping mains. High pressure may burst the pipes, joints and fittings, or damage pumps. A pressure relief (safety) valve opens automatically when the pressure goes above a set limit, discharges the excess water and protects the pipeline. It is also used on the delivery side of pumps and where water hammer is expected.

Construction and working

          adjusting screw
              |
           [spring]
              |
        ___ [plug] ___
   =====|__ valve seat __|===== pipe
               |
          discharge pipe -> drain
  • A spring-loaded (or dead-weight) valve sits on a seat on a branch connected to the pipeline.
  • The spring is adjusted to the maximum allowed pressure.
  • When the pressure in the pipe exceeds this value, it lifts the valve off its seat and water escapes through the discharge pipe, so that the pressure goes down.
  • When the pressure falls below the set value, the spring closes the valve again.
  • A relief valve is placed near the pump delivery or at the points of high pressure; the discharge is led to a drain.

✓ Answer checked by Claude Opus 5.5 (high effort)

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