TL;DR
Identify whether the noise comes from the combustion side (burner, air blower, or flue gas ductwork) or the steam/water side. Combustion pulsation needs air-fuel ratio adjustment. Steam-side banging is water hammer.
What you might see
- rumbling or pulsating noise from the combustion chamber
- banging noise from the steam side of the boiler
- high-pitched whining from the combustion air blower
- vibration in flue gas stack or breeching
Likely causes
Combustion pulsation from an unstable flame caused by incorrect air-fuel ratio
Water hammer in the steam distribution system (see the water-hammer procedure on this machine)
Worn combustion air blower bearings or an imbalanced blower wheel
Thermal expansion noise from piping or refractory expanding and contracting
Required tools
- LOTO kit
- Combustion analyzer
- Contact stethoscope or steel rod for noise isolation
- Vibration meter
Safety first
- Do not attempt to open the burner housing or inspect the combustion chamber while the boiler is firing.
- Lock out the burner completely before rotating the combustion air blower by hand.
Procedure
- 1
Identify the noise type and location. Use a contact stethoscope or a piece of rod held to the surface to isolate whether the noise comes from the combustion chamber, the steam drum, or the air blower.
- 2
If the noise is a rhythmic pulsation from the combustion chamber synchronized with the firing cycle, check the air-fuel ratio setting with a combustion analyzer (see the excessive-fuel-consumption procedure on this machine).
- 3
Check the combustion air blower. Lock out the burner and rotate the blower wheel by hand. Roughness or wobble indicates worn bearings.[1]
Warning: Lock out the burner completely before rotating the blower wheel by hand. - 4
Measure combustion air blower vibration with a vibration meter at the blower bearing housing. Compare to baseline.[1]
- 5
If the noise is a banging on the steam side, follow the water-hammer diagnosis procedure on this machine.
- 6
Inspect flue gas ductwork, stack breeching, and damper blades for loose fasteners or worn blades that can resonate at certain flow rates.
- 7
If combustion pulsation cannot be resolved by air-fuel adjustment, contact Cleaver-Brooks service. Severe pulsation can cause refractory damage and stress the pressure vessel.
Sources
Cleaver-Brooks CB Firetube Boiler Operation, Service, and Parts Manual, Cleaver-Brooks
Cleaver-Brooks CB Boiler Operation, Maintenance and Parts Manual, burner noise and combustion stability troubleshooting (general)
View source
More guides for Cleaver-Brooks CB / CBLE
How to reduce excessive fuel consumption on a Cleaver-Brooks CB boiler
Excess fuel use is almost always excess air in the combustion process or degraded heat transfer surfaces. Run a flue gas analysis to set the air-fuel ratio correctly, then check for scale and soot.
How to diagnose flame failure on a Cleaver-Brooks CB boiler
Most flame failure lockouts are a contaminated flame detector (UV cell or flame rod), a failed igniter, or a fuel supply problem. Clean the flame detector first. It fixes the fault in the majority of cases.
How to fix low steam pressure on a Cleaver-Brooks CB boiler
Low steam pressure with the boiler at full fire means heat transfer is degraded, most often from fireside soot or waterside scale. Compare flue gas exit temperature to baseline: a rise of more than 10 degrees C per 100 hours indicates fouling.
How to respond to a safety valve lifting on a Cleaver-Brooks CB boiler
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.
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