Safety valves

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safety valves
classification
erection
parts
requirement
locations
testing

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Safety valves

  1. 1. WELCOME
  2. 2. SAFETY VALVES
  3. 3. SAFETY VALVES • To protect systems or vessels from excessive pressure
  4. 4. According to construction 1) Dead weight 2) Lever type 3) Spring
  5. 5. According to operation 1) Pneumatic 2) Solenoid 3) Steam
  6. 6. Safety valves To provide immediate relief of over pressure by making rapid full opening for compressive fluids.( air, gases and steam) There should not be any isolation valve before safety valve.
  7. 7. Relief valve To relieve excessive pressure in system containing incompressive fluids. Generally have gradual lift proportional to the increase in pressure. ( oil & water)
  8. 8. Safety relief valve - It is an automatic pressure-relieving device whose open and close movements are fully controlled by source of power – such as air,steam and hydraulic. - It may be operated manually as desired at any pressure.
  9. 9. Non-Reclosing PRV - It is designed to remain open after operation.
  10. 10. Vacuum relief valve •Designed to admit fluid to prevent an excessive internal vacuum. •It is designed to re-close and prevent further flow of fluid after normal conditions have been restored.
  11. 11. REQUIREMENT OF SAFETY VALVE - Proper functioning - Opening at correct set pressure - Correct blow down - Proper mechanical operation & Clean closure without leakage.
  12. 12. As per boiler regulations, every boiler shall have the following mountings 1. Two safety valves 2. Two water level indicator 3. A steam pressure gauge 4. A steam stop valve 5. A feed check valve 6. Two feed pump 7. A Blow down valve
  13. 13. LOCATIONS • Drum • Super heaters • Reheaters • Aux. Steam headers • Deaerators • Oil heaters • Soot blower systems
  14. 14. CHATTERING - Rapid opening and closing of the valve is known as chattering. CAUSES - Insufficient blow down - More back pressure due to under size discharge piping - Insufficient steam flow to the valve - lifting with water
  15. 15. SIMMERING The valve is just about to open and has indefinite contact. An audible sound or visible escape of fluid between seat and disc at an inlet static pressure below the popping pressure and at no measurable capacity.
  16. 16. FLUTTER • Flutter is an abnormal, rapid reciprocating motion of the safety valve stem, in which the disc does not contact the seat.
  17. 17. Blow down Opening pressure – Closing pressure ----------------------------------------------- X 100 Opening pressure
  18. 18. Important codes governing safety valves 1) IBR – 1950 2) ASME Sec- I Power boilers 3) ASME Sec – VIII 4) BS - 756
  19. 19. General conditions for safety valves - Drum safety valves should be 75% of evaporating capacity - Super heater safety valves should be 50% of evaporating capacity - Both drum & super heater safety valves discharge capacity should be more than 100% evaporating capacity.
  20. 20. - Each Reheater safety valves shall discharge more than 20% of evaporation. - All reheater safety valves combined should be more than 100% evaporating capacity.
  21. 21. - Inlet connection should be welded for high pressure safety valves. - Safety valves should be full lift type. - Blow down should be 3 to 5 %. - Easy maintenance - No seat tightness problems - No Chatter problems - Economy
  22. 22. PARTS OF SAFETY VALVE Body , Yoke Stem , Seat bushing, Spring, Disc, spring retainer plates, Compression screw, Cross bar, upper & lower rings
  23. 23. DISMANTLING Ensure availability of tools Availability of spares Taking measurements Thorough inspection Check condition of stem,seat, spring & disc.
  24. 24. OVERHAULING Cleaning of all parts Lapping of seat & disc Spindle run out Replace defective parts Painting
  25. 25. ASSEMBLING Use Molykote lubricant Assemble as per sequence Maintain recommended readings Tightening of all bolts & Nuts.
  26. 26. UPPER RING ADJUSTMENT - To shorten the blow down raise upper ring. - To increase the blow down lower upper ring
  27. 27. LOWER RING ADJUSTMENT - To obtain clean popping action - To cushion the closing action of the valve - Reduces simmering
  28. 28. FILED TESTING • Use of hydro set unit • Full system pressure • Valve should be set with in 1% of set pressure • Valve should be hand popped at 75 to 80% of set pressure
  29. 29. GAGGING - Arresting the stem mechanically from lifting. - Do not gag in cold condition - Gag at 80% of low set value pressure.
  30. 30. FLOATING - Calibrated gauges are to be used. - Test and achieve within minimum number of pops. - Apply gag load finger tight only - Remove gags after floating - Bring Blow down between 3 and 5 %
  31. 31. MAINTENANCE • The recommended spares and tools are to be made available. • Flat lapping plate. • High temperature lubricant. • Lapping compound of grit size • 320 – general, 500- finishing & 1000 for polishing
  32. 32. - Step height shall be 0.635 MM, if it is less than 0.254 MM, seat cutting is to be done. - Spindle run out should be with in 0.177 MM.
  33. 33. SAFETY PRECAUTIONS - Don’t go near discharge side - Body drain and vent must be piped to safe area - Gag the valve during ring adjustment - Hand pop with 5 to 6 Mts safe rope) - Use ear muffs / hand gloves - Adequate access around the valve for maintenance works.
  34. 34. PROCUREMENT OF SAFETY VALVE - Inlet & outlet size - Inlet & outlet construction - Flow - Medium details - Blow down - Set pressure - Body material - IBR requirement
  35. 35. ERECTION - Flanged - Welded – dismantling - Preheating & post heating - Verticality - Vent pipe orientation - Accessibility
  36. 36. THANK YOU

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