---
title: "Water cannon"
description: "A water cannon projects a high-pressure water jet onto boiler waterwall tubes to crack slag deposits by thermal shock. The rapid temperature differential between the cool water and the hot slag fractures the bonded slag layer, allowing the next portion to fall away. Water cannons are the standard cleaning tool for furnace slagging on coal-fired and biomass utility boilers."
canonical_url: "https://sylio.co/glossary/water-cannon"
last_updated: "2026-06-28T02:29:24.551Z"
---

A **water cannon** projects a high-pressure water jet onto boiler [waterwall](/glossary/waterwall) tubes to crack slag deposits by thermal shock. The rapid temperature differential between the cool water and the hot slag fractures the bonded slag layer, allowing the next portion to fall away. Water cannons are the standard cleaning tool for furnace [slagging](/glossary/slagging) on coal-fired and biomass utility boilers.

## Aimed shots, not sweeps

Modern *smart* water cannons (notably Clyde Bergemann) are computer-controlled to aim specific shot patterns at known fouling zones. Operators see a heat-flux map from radiant-section thermocouples; the cannon fires shots calibrated to the slag thickness in each zone. Compared with manual aiming, this dramatically reduces water consumption and tube-fatigue risk.

## Trade-offs

- **Tube fatigue** — repeated thermal cycling can crack tubes at the impingement zone over years of service
- **Water consumption** — substantial volumes of demineralised water needed
- **Slag knock-down hazard** — large fallen slag pieces can damage waterwall lower zones
- **Effective only on slag** — does not address dry friable deposits on convective surfaces

[Sonic horns](/glossary/sonic-horn) are not effective on furnace slag and water cannons are not effective on dry convective-pass deposits. The two technologies serve different zones of the boiler and do not directly compete.

## Related terms

- [Water lance](/glossary/water-lance)
- [Waterwall](/glossary/waterwall)
- [Slagging](/glossary/slagging)
- [Steam sootblower](/glossary/steam-sootblower)