Lets Know about Relief Valve and Safety Valve


  • Mounted  in bottleAir, Heat exchanger, hydrophore, positive displacement pump.
  • let say if we set pressure at 30 bar, then safety valve lifts at slightly above above set pressure i,e. 30.1 bar.
lifting of relief valve is gradual according to the pressure.
        (example) - Set value, 30 bar
              30.1bar - will open slightly.
              35bar     - will open full.
     Relief valve is directly proportional to the pressure increase.

  • If pressure decreases bellow the set value then valve closes. 


  • Mounted in boiler economiser, superheater, (can also be used in gear pumps and screw pumps.
  • let say, boiler operated at 7 bar pressure.
          safety valve opens at set pressure, if set pressure is 7 bar then safety valve opens              at 7 bar.
         safety valve sits at 3 to 4% below the set valve pressure.
  • For example if 7 bar is set pressure then valve sits at 4.5 bar.
  • This is done by lip - 
  • The function of lip is creates extra lift so that there is enough pressure drop when the safety valve lifts or safety valve blowdown.

  • In safety valve the blowdown period is large when compared to blowdown period of relief valve.
  • I.H.L(Improved High Lift ) safety valve -wasting piston is provided which creates extra lift.
  • Both lip & wasting piston create enough pressure difference.

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