Safety valves

safety valves
classification
erection
parts
requirement
locations
testing

1. WELCOME

2. SAFETY VALVES

3. SAFETY VALVES
•To protect systems or vessels
from excessive pressure

4. According to construction
1) Dead weight
2) Lever type
3) Spring

5. According to operation
1) Pneumatic
2) Solenoid
3) Steam

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. Relief valve
To relieve excessive
pressure in system containing
incompressive fluids.
Generally have gradual lift
proportional to the increase in
pressure.
( oil & water)

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. Non-Reclosing PRV
- It is designed to remain open after
operation.

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. REQUIREMENT OF SAFETY
VALVE
- Proper functioning
- Opening at correct set pressure
- Correct blow down
- Proper mechanical operation &
Clean closure without leakage.

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. LOCATIONS
• Drum
• Super heaters
• Reheaters
• Aux. Steam headers
• Deaerators
• Oil heaters
• Soot blower systems

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. 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. FLUTTER
•Flutter is an abnormal, rapid
reciprocating motion of the safety
valve stem, in which the disc
does not contact the seat.

17. Blow down
Opening pressure – Closing pressure
----------------------------------------------- X 100
Opening pressure

18. Important codes governing
safety valves
1) IBR – 1950
2) ASME Sec- I Power
boilers
3) ASME Sec – VIII
4) BS - 756

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. - Each Reheater safety valves shall
discharge more than 20% of evaporation.
- All reheater safety valves combined
should be more than 100% evaporating
capacity.

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. PARTS OF SAFETY VALVE
Body , Yoke
Stem , Seat bushing, Spring,
Disc, spring retainer plates,
Compression screw,
Cross bar,
upper & lower rings

23. DISMANTLING

Ensure availability of tools
Availability of spares
Taking measurements
Thorough inspection
Check condition of stem,seat,
spring & disc.

24. OVERHAULING
Cleaning of all parts
Lapping of seat & disc
Spindle run out
Replace defective parts
Painting

25. ASSEMBLING
Use Molykote lubricant
Assemble as per sequence
Maintain recommended readings
Tightening of all bolts & Nuts.

26. UPPER RING ADJUSTMENT
- To shorten the blow down raise
upper ring.
- To increase the blow down
lower upper ring

27. LOWER RING ADJUSTMENT
- To obtain clean popping action
- To cushion the closing action of the
valve
- Reduces simmering

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. GAGGING
- Arresting the stem mechanically from
lifting.
- Do not gag in cold condition
- Gag at 80% of low set value pressure.

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. 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. - 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. 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. PROCUREMENT OF SAFETY
VALVE
- Inlet & outlet size
- Inlet & outlet construction
- Flow
- Medium details
- Blow down
- Set pressure
- Body material
- IBR requirement

35. ERECTION
- Flanged
- Welded – dismantling
- Preheating & post heating
- Verticality
- Vent pipe orientation
- Accessibility

36. THANK YOU