SAFETY VALVE ON BOILER

Regulation for Safety Valve -:

1. There are 2 safety valves. Both the safety valves are to be set at a pressure not exceeding 3% of the normal working pressure .
2. The safety valves must be capable of releasing the maximum amount of steam the boiler can evaporate,while still keeping within the 10 percent accumulation of pressure rule.
3. Boiler safety valve is set to lift at any pressure, but not more than 3% above working pressure. Also the safety Valve re-sits at 5% below working pressure.

Safety Valve Setting Procedure:


1. The boiler comprises of 2 safety valves set at different lifting pressures. The valve, which is to be set at lower pressure, is locked in position by the “gagging tool”.

2. The valve not to be set is gagged when the boiler pressure reaches 80%. 

3.Raise the steam pressure and simultaneously tighten the gagging tool. Care must be taken not to over-tighten the gagging tool as it may lead to bending of valve spindle or other problem.

4. If due to insufficient tightening leakage of steam occurs, decrease the pressure until the leakage stops and then retighten the gag.

5. Operated hand-easing gear at about 90% of the set pressure of the valve. If the valve lifts before or after the set pressure, decrease the boiler steam pressure to 90% of the safety valve setting and then adjust the setting screw accordingly. 

6. If setting of safety valve pressure is required to be increased, tighten the setting screw and vice versa. Ensure to tighten the locking screw each time the setting procedure of safety valve pressure is performed.


Difference between safety valve and relief valve 


Safety valve

1) A safety valve is a device designed to actuate automatically to release excess pressure. 

2) A safety valve has a pop up action and open immediately. 

3) Setting pressure is just above the working and not more than 3% above the approved working pressure. 

Relief valve

1) It is used to limit the pressure in the system within specific limit.

2) Opening is proportion to the increase in pressure (gradual action).

3)Setting pressure is 10% above working pressure . 


Marking on safety valve 

1. Manufacturer’s name 

2. Serial number 

3. Inlet diameter 

4. Operating pressure 

5. Discharge capacity 

6.  Safe working pressure 

7. Blow off pressure


Boiler safety valve checks &  attention during overhauling

1. Checked its valve and valve seat for wear, cavity corrosion and any fault.

2. They should be grounded properly but maker’s limit must be maintained such as width of seating, clearance betweenvalve lip and seat. 

3. Valve chest must be cleaned condition and drain line clear. 

4. The spring should be hammer tested for any fracture and check for corrosion.

5. Free length islimited to 0.5 % of original free length. 

6. The spindle should be hammer tested for any crack and its straightness. 

7. The guide plates and bushes are checked for uneven wear and have sufficient clearance to allow free movement of spindle.

8. The compression nut and cover bush’s threads are carefully checked it for any sign of wear and ttear 

9. The easing gear should be checked in good order including bearings, cable pulley, and connecting links.

10. Connecting pin should be a free fit in the lid  and pin should not bent or pinhole gone out of shape 

11. All safety valves are to be set to operate under steam a little above   working pressure not greater than 3% above the approve working pressure of the boiler. 

 

WHY SAFETY VALVE IS FITTED IN TWO NUMBERS

To make sure that the positive discharging of higher steam pressure from boiler efficiency. 

WHY FITTED IN ONE VALVE CHEST 

- To reduce stress by hole on pressure vessel (boiler) 

- To minimize the numbers of cutting hole on boiler to save it's strength.

FUNCTION OF EASING GEAR 

Easing gear is fitted basically to allow for manual operation of the safety valve, in case of failure to open when the boiler has been over pressurized. It has mainly two  purposes.

  1. To manually operate the safety valve.
  2. To regularly test the safety valve

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