TL;DR
A lifting safety valve means the pressure controls failed to cut the burner at the operating setpoint. Inspect the operating pressure control and high-limit control for proper setpoint and contact operation. Do not attempt to adjust or prevent the safety valve from lifting.
What you might see
- safety valve lifting and discharging steam
- boiler pressure rising above the operating pressure setpoint
- operating pressure limit control not cutting the burner at setpoint
- burner running continuously past the normal cutout point
Likely causes
Operating pressure control set too high or its contacts not opening at the setpoint
High-limit pressure control failed or set above the safety valve setpoint
Safety valve lifting at set pressure due to normal operation, then not re-seating cleanly
Pressure gauge reading incorrect, leading to a wrong setpoint adjustment
Required tools
- LOTO kit
- Calibrated test pressure gauge
- Multimeter for pressure control contact test
Safety first
- A boiler with a lifting safety valve is over-pressure. Keep all personnel away from the steam discharge area.
- Never block, bypass, or tamper with a safety valve. This creates an explosion hazard and is a regulatory violation.
- After any safety valve lift, have the valve inspected and tested before returning the boiler to service.
Procedure
- 1
Do not interfere with the safety valve while it is lifting. The safety valve is the last line of protection.
Warning: Never wire, block, or weight a safety valve open or closed. This is illegal and creates an imminent explosion hazard. - 2
Observe the boiler pressure on the calibrated pressure gauge. Confirm whether the operating pressure limit control has opened its contacts and cut the burner.
- 3
If the burner is still firing above the operating cutout setpoint, manually trip the burner from the emergency stop.
Warning: Do not attempt to reduce boiler pressure by opening blowdown valves or increasing steam load to process. Allow the safety valve to control pressure. - 4
Lock out the burner after the manual trip. Allow the boiler to cool before any electrical inspection.
- 5
Inspect the operating pressure control: verify its setpoint, clean the contacts, and check that the contacts open cleanly at the set pressure using a calibrated test gauge.[1]
- 6
Inspect the high-limit pressure control for the same. Both controls should be tested and calibrated annually by a qualified boiler technician.[1]
- 7
After the pressure controls are verified or replaced, have the safety valve inspected by a valve service shop. A safety valve that has lifted may not re-seat correctly and should be replaced.
- 8
Document the event in the boiler log and notify the facility manager and the boiler insurance inspector.
Sources
Cleaver-Brooks CB Firetube Boiler Operation, Service, and Parts Manual, Cleaver-Brooks
Cleaver-Brooks CB Boiler Operation, Maintenance and Parts Manual, pressure control system and safety valve maintenance (general)
View source
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