Clear steps for Boiler Safety valves major overhauling

 Boiler Safety valve major overhauling steps

  • Cleaning of safety valve
  • Complete dismantling of safety valve.
  • Cleaning, polishing & buffing of parts.
  • Thorough inspection of all parts.
  • Seat & disc lapping
  • Spindle run out (bend) checking
  • Spring checking for any abnormalities like crack, bend, reduced tension etc
  • Lapping of both disc & seat.
  • Inspection of upper & lower ring teeth for damage/crac
  • Measurement & re-assembly.
  • Inspection of discharge pipe connection. If there is telescopic discharge pipe, then ensure a gap of minimum 10 mm for thermal expansion.


1-After seat & disc lapping, place lower nozzle ring on seat & level both the faces

Questions & Answers on Safety valves

2-After leveling, turn the lower ring by 3 notches in clockwise direction.

For example if Safety valve’s operating pressure is 117 kg/cm2, then 117 kg/cm2/42.4 kg/cm2 = 2.75 Appx. 3 Nos i.e 42.4 kg/cm2 for every notch (For more details, refer manufacturing data)

 Then lock the lower ring by inserting lower set screw

3- Take measurement from seat top to guide (89-90mm)                                          

4-Then measure the length of upper ring (it should be same as seat top to body top) & place it into the body

5-Fit disc to spindle then place disc with disc holder & spindle into the body & lock it by set screw

6-Put a body on spindle & lock the spindle by split pins & adjust the lift ,to increase the lift , rotate the lift stop collar clockwise & to decrease the lift, rotate the collar in anticlockwise direction. For every one full rotation, 1.58 mm lift can be adjusted.

7-Then fit the lower spring washer & helical compression spring

8-Then fit upper washer & yoke assy. thrust bearing & spindle lock nuts 

Basic concepts of safety valves


To increase the blow down: Lower the upper ring by 7 notches for 1Kg/cm2

To decrease the blow down: Raise the upper ring by 7 notches/1 Kg/cm2

To reduce shimmering: Raise the lower ring by one notch up, if not adjusted again rise one notch up. This is allowable till ring levels seat top.


 Power plant Safety QnA

 Boiler calculations for Boiler exam operation engineer (BOE)

 Attemperation & related calculations



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