Module 08 · Condensate Recovery4 min read
Water Hammer in Steam Systems: Causes and Cures
Water hammer is the bang in a steam line, and it is a warning. It means water is where it should not be, moving faster than it should. The loud ones break fittings and can injure people; the quiet ones loosen joints over months.
You'll learn
- Distinguish the two main kinds of water hammer
- Identify the causes in a steam system
- Know the damage it does
- Prevent it by design and operation
Before this: Main drainage and warm-up load, Return lines and condensate pumps
BeginnerThe idea in plain words, and where you meet it. No maths.
Two kinds of hammer
- Slug hammer: condensate collects in a steam main, the fast-moving steam picks up a slug of it and throws it at a bend, valve or closed end. The slug stops suddenly and the impact bangs.
- Condensation-induced hammer: steam meets cold water, condenses suddenly, and leaves a void. Water rushes in to fill it from both sides and collides. Common where steam enters a pipe or vessel partly full of cooler water.
Both happen fastest on start-up, when mains are cold and full of condensate, and in return lines and heat exchangers where steam and water meet.
IntermediateThe formula, its units, and a worked example on real plant numbers.
Causes
| Cause | Where |
|---|---|
| Undrained low points and sags | Steam mains and branches |
| Drain traps sized on running load only | Mains at every cold start |
| Opening steam valves fast into a cold, wet main | Boiler stop valve, branch valves |
| Failed-closed traps flooding equipment | Heat exchangers, coils |
| Undersized or uphill return lines | Trap discharge and return lines |
| Stalled heat exchangers | Temperature-controlled equipment with lifted returns |
| Carryover from the boiler | Mains after load surges |
ExpertThe fine print: where the simple model breaks, and what it costs.
Cures
- Drain mains properly: slope with the flow, full-size drip legs at every low point and riser, traps sized for warm-up load.
- Warm up slowly: open the main stop and branch valves gradually with drains open; some plants fit small warm-up bypass valves.
- Eliminate sags: support mains at proper intervals so that they cannot form pockets.
- Fix stall: fit pumping traps or pressure-powered pumps where temperature-controlled equipment cannot drain against its return.
- Size and route returns correctly: for flash volume, sloping down, without high-pressure discharges into low-pressure lines.
- Keep the boiler from carrying over: correct TDS and water level, and gradual loading.
Key takeaways
- Slug hammer: steam throws condensate into fittings. Condensation hammer: steam collapses in cold water.
- Undrained mains, fast warm-up, flooded equipment, poor returns, stall and carryover cause it.
- Cure by drainage sized for warm-up, slow start-ups, no sags, correct returns and fixing stall.
- Hammer is a warning of real damage, not just noise.