TL;DR
Water hammer means condensate is pooling in the steam line and being picked up by high-velocity steam. Check that all drip legs are sized correctly, steam traps are discharging, and the system is warmed up slowly before opening the main steam valve.
What you might see
- loud banging or knocking in steam lines
- vibration in steam piping felt on adjacent structures
- condensate pooling at low points in steam lines
- trap discharge inconsistent or cold at drip legs
Likely causes
Condensate accumulation at low points in the distribution piping from missing or undersized drip legs
Failed-closed steam traps not discharging condensate from drip legs
Main steam valve opened too rapidly, pushing condensate slugs at high velocity
Piping slope reversed or insufficient (less than 1 in 40) preventing condensate drainage
Required tools
- Ultrasonic steam trap tester or IR thermometer
- LOTO kit
- Heat-resistant gloves and eye protection
- Replacement steam traps (correct type and orifice size)
Safety first
- Steam and near-boiling condensate cause severe scalding burns. Wear heat-resistant gloves and face shield when working near steam lines or testing traps.
- Water hammer can crack or displace piping and fittings. Inspect the affected piping for cracks or shifted joints after a severe hammer event.
Procedure
- 1
When starting from cold, open the main steam valve slowly over at least 5-10 minutes to allow the system to warm up and condensate to drain through the traps before full pressure is applied.[1]
- 2
Check all drip legs in the steam distribution system. Each drip leg should be at least the nominal pipe diameter in depth to provide a condensate reservoir.[1]
- 3
Test each steam trap at the drip legs using an ultrasonic detector or IR thermometer. A trap that shows upstream temperature but no discharge activity is failed-closed. Replace it.
Warning: Steam traps discharge near-boiling condensate. Wear heat-resistant gloves and eye protection when testing. - 4
Inspect the piping slope. Steam lines should slope at least 1 in 40 toward the condensate return or drip legs. A level or uphill line will accumulate condensate regardless of trap size.
- 5
After verifying trap operation and drip leg sizing, restart the boiler using the slow warmup procedure. Confirm hammer does not recur.
- 6
If hammer persists on a correctly installed and sloped system, consult a steam system specialist. The system may have been modified to create a low point with no drip leg.
Sources
Cleaver-Brooks CB Firetube Boiler Operation, Service, and Parts Manual, Cleaver-Brooks
Cleaver-Brooks CB Boiler Operation, Maintenance and Parts Manual, steam distribution and condensate management (general)
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