Inverted bucket steam traps operate using a simple mechanical principle based on buoyancy. Inside the trap is an upside-down “bucket” connected to a valve.

When steam enters the trap, it fills the bucket, causing it to float.

As the bucket rises, it pulls the valve closed, preventing live steam from escaping.

A small vent hole in the top of the bucket allows air and non-condensable gases to pass through during start-up, ensuring the system warms up quickly and efficiently.

As condensate forms and replaces the steam, the bucket loses buoyancy and begins to sink.

This downward movement opens the valve, allowing condensate to discharge.

Once the condensate has been expelled and steam re-enters the trap, the bucket floats again and the valve closes.

This cyclical action means inverted bucket steam traps only open in the presence of condensate and remain tightly sealed when steam is present, delivering zero steam loss in normal operation.

Their rugged, all-mechanical design makes them exceptionally resistant to water hammer, dirt, and harsh operating conditions.

Spirax Sarco Inverted Bucket Steam Traps are trusted across industry for one reason: they keep working where others fail. Designed to handle water hammer, vibration, and dirty condensate, these traps are ideal for high-pressure and demanding steam services. The HM Series in cast iron provides dependable performance on plant mains and general duties, while the S and SF Series offer compact, maintainable solutions with integral strainers for smaller pipe sizes and distribution lines.

For heavier industrial environments, the SCA Series carbon steel inverted bucket traps deliver robust in-line performance across a wide pressure range, with part codes such as SCA15, SCA30, and SCA40 covering everything from light process loads to high-demand plant applications. In vertical and high-pressure duties, the IBV range takes over. Options include IBV Series C in carbon steel, IBV Series C-LF2 for low-temperature services, and the IBV Series Z in alloy steel for superheated steam and extreme conditions. Each IBV variant is engineered for rapid valve closure with no steam loss, making models like IBV-C, IBV-LF2, and IBV-Z ideal for refineries, power plants, and critical process systems.

Whether it’s an SFA8 on a small branch line, an SCA30 on a process drain, or an IBV-Z on a high-pressure main, Spirax Sarco inverted bucket steam traps provide mechanical reliability that thrives under pressure—delivering long service life, zero steam loss in operation, and dependable condensate removal across the toughest steam environments.