WELCOME
SAFETY VALVES
SAFETY VALVES
• To protect systems or vessels from excessive pressure
According to construction
1) Dead weight
2) Lever type
3) Spring
According to operation
1) Pneumatic
2) Solenoid
3) Steam
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.
Relief valve
To relieve excessive pressure in system containing incompressive fluids.
Generally have gradual lift proportional to the increase in pressure.
( oil & water)
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.
Non-Reclosing PRV
- It is designed to remain open after
operation.
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.
REQUIREMENT OF SAFETY VALVE
- Proper functioning
- Opening at correct set pressure
- Correct blow down
- Proper mechanical operation &
Clean closure without leakage.
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
LOCATIONS
• Drum• Super heaters• Reheaters• Aux. Steam headers• Deaerators• Oil heaters• Soot blower systems
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
SIMMERINGThe 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.
FLUTTER
• Flutter is an abnormal, rapid reciprocating motion of the safety valve stem, in which the disc
does not contact the seat.
Blow down
Opening pressure – Closing pressure
----------------------------------------------- X 100
Opening pressure
Important codes governing safety valves
1) IBR – 1950
2) ASME Sec- I Power boilers
3) ASME Sec – VIII
4) BS - 756
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.
- Each Reheater safety valves shall
discharge more than 20% of evaporation.
- All reheater safety valves combined
should be more than 100% evaporating
capacity.
- 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
PARTS OF SAFETY VALVE
Body , Yoke
Stem , Seat bushing, Spring,
Disc, spring retainer plates,
Compression screw,
Cross bar,
upper & lower rings
DISMANTLING
Ensure availability of tools
Availability of spares
Taking measurements
Thorough inspection
Check condition of stem,seat,
spring & disc.
OVERHAULING
Cleaning of all parts
Lapping of seat & disc
Spindle run out
Replace defective parts
Painting
ASSEMBLING
Use Molykote lubricant
Assemble as per sequence
Maintain recommended readings
Tightening of all bolts & Nuts.
UPPER RING ADJUSTMENT
- To shorten the blow down raise
upper ring.
- To increase the blow down
lower upper ring
LOWER RING ADJUSTMENT
- To obtain clean popping action
- To cushion the closing action of the
valve
- Reduces simmering
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
GAGGING
- Arresting the stem mechanically from
lifting.
- Do not gag in cold condition
- Gag at 80% of low set value pressure.
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 %
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
- 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.
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.
PROCUREMENT OF SAFETY VALVE
- Inlet & outlet size - Inlet & outlet construction
- Flow - Medium details - Blow down - Set pressure - Body material - IBR requirement
ERECTION
- Flanged
- Welded – dismantling
- Preheating & post heating
- Verticality
- Vent pipe orientation
- Accessibility
THANK YOU
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