Inverted Bucket Steam Traps

How It Works

The inverted bucket trap uses a buoyant bucket that is open at the bottom and inverted (opening facing down) inside the trap body. When steam enters the trap, it fills the bucket, making it buoyant. The bucket rises and closes the discharge valve.

When condensate enters, it displaces the steam from the bucket. The bucket loses buoyancy, sinks, and opens the discharge valve. Condensate flows out. When steam arrives again, the cycle repeats. A small bleed hole in the bucket allows trapped steam to escape slowly, preventing the trap from air-binding.

Advantages

• Rugged and long-lasting: Few wearing parts, robust construction — can last 10+ years with proper maintenance.
• Good water hammer resistance: The bucket mechanism is more tolerant of water hammer than float traps.
• Clear failure mode: When it fails, it typically fails open — discharging steam, which is visible and easy to detect.
• Handles high pressure: Suitable for high-pressure steam mains and superheated steam (with a check valve).

Disadvantages

• Can air-bind: If the bleed hole is blocked, air accumulates in the bucket and the trap stops cycling. The system must have separate air vents.
• Intermittent discharge: Like thermodynamic traps, bucket traps cycle on/off — not ideal for applications requiring continuous condensate removal.
• Sensitive to back pressure: If condensate return pressure is high, the trap may not open. Needs sufficient differential pressure.
• Can lose prime: If steam pressure drops suddenly, the water seal can be lost, allowing steam to blow through.

Common Applications

Inverted bucket traps are commonly found on mainline drip legs, steam tracing lines, and older process equipment. They are being increasingly replaced by thermodynamic traps (for drip legs) and float traps (for process loads), but many are still in service and performing reliably.