.boiler
Safety Valve Sketch, setting and Testing. Label all parts and materials
Safety v/v Setting
.bsvs .boiler safety valve setting
- Safety valve to be overhauled and reset at every survey
- At least 2 calibrated pressure gauge required
- Loosen lock nut, screw down the compression screw few more turns then previous setting. Measure the height make marking
- With all mounting in place, shut the main steam stop valve.
- Fire the boiler on auto
- Once boiler auto cut off, switch to manual. Rise the boiler manually till require set pressure
- At this setting, unscrew the compression till safety valve lift
- Fire the boiler continuously and check the safety valve lift at set pressure
- Stop the boiler and check safety valve sit firmly at seating and no leakage
- Safety valve now has been adjusted, tighten lock nut. This valve then had to be gagged
- Set the other safety valve in same procedure
- But this valve is usually set about 3% higher than the earlier valve
- Remove the gagging tool.
- Lift the safety valve with easing gear and confirm it sit firmly and no leakage.
boiler safety valve SOLAS requirement
.bsvr .boiler safety valve .svr .boiler safety valve regulation
- Each boiler (including exhaust gas boiler) is to be fitted with at least one safety valve and where the water-heating surface area is more than 46.5 m2, two or more safety valves are to be provided.
- Quick Estimation of heating surface area = Π x D x L x N (circumferential area of tubes)
≠ Π/4 x D2 x L x N (this is for flow calculation)
D = dia. of tube, L = length of tube,
N = total number of tubes
- Valve Size
- The safety valve bore must be between 19 to 100 mm
- (Some class/countries use the imperial system of ¾” to 4” example ABS)
2. Accumulation Pressure Test
- With the steam stop valve shut and the boiler burner firing continuously at full-load capacity, the maximum pressure built up in the boiler should not exceed 6% above the maximum allowable working pressure
- It is also conducted during the commissioning test.
Purpose: To ensure the safety valve relieving capacity matches the rated steam generation rate.
3. Safety Valves relieving capacity
- The aggregate relieving capacity of the safety valves must not be less than the evaporating capacity of the boiler under maximum operating conditions.
Purpose: Biggest safety valve is 100 mm bore.
100 mm bore = 50,000 kg/hr
If your maximum evaporation rate is 100,000 kg/hr, then you need 2 pairs of safety valves. ULCC/VLCC tankers have been known to have 2 pairs of safety valves
4. Easing Gear
- Each safety valve is to be fitted with an easing gear by which the safety valves can be operated from a safe platform either by hand or by mechanical means.
Purpose: – To carry out routine functional/ operational test of the safety valve
– To release excessive steam pressure in an emergency.
- Escape Pipe (Outlet of safety v/v)
- The area of the escape pipe must be equal or greater than the outlet area of each safety valve
- The pipe should be free of any restriction
Purpose:
- To prevent build-up of steam pressure in the escape pipe
- No valves to be fitted so that if the valve is shut, then safety valve becomes useless
Blowdown of safety valve:
Link: https://shipsengine.com/blowdown-meaning-of-a-boiler-safety-valve/
- Blowdown = Opening Pressure – Closing Pressure
- Too Little Blowdown
- Rapid opening and closing of the valve can cause the valve and seat to get damage Also called the ‘chattering effect’
- Too Much Blowdown
- Unnecessary loss of steam pressure
- Not economical as heat energy, water, boiler chemicals etc lost