Steam Trap Types: Thermodynamic, Thermostatic, Float and Inverted Bucket

A steam trap discharges condensate, air and other non-condensable gases from a steam system while keeping live steam inside. If condensate stays in the system, heat transfer slows down, corrosion increases, water hammer can occur and energy is wasted. Choosing the right steam trap type for each point is what keeps a steam system efficient. For the basics, read what is a steam trap and how does it work.

This guide compares the four most common types — thermodynamic, thermostatic, float and inverted bucket — with their operating principles, advantages and applications.

Steam Trap Types at a Glance

Thermodynamic Steam Traps

Thermodynamic traps use the difference in pressure and velocity between condensate and live steam. A disc rises when condensate arrives and lets it out; when steam arrives, the disc closes and keeps the steam in.

Advantages: compact and robust, resistant to water hammer and high pressure, works over a wide pressure range, easy to maintain, frost resistant outdoors. Limitations: may cycle noisily at low loads; the disc wears over time.

Applications: steam mains and drip legs, tracing lines, drying systems, irons and presses, superheated and high-pressure lines.

Thermostatic Steam Traps

Thermostatic traps sense the temperature difference between steam and condensate with a bimetallic element or a capsule. Cooler condensate opens the valve; when steam arrives, the rising temperature closes it.

Advantages: high energy efficiency, uses sensible heat of the condensate, quiet operation, excellent air venting. Limitations: slower response to sudden load changes; performance depends on correct installation.

Applications: tracing lines, air venting at equipment and line ends, sterilisers and small heaters, steam-jacketed pipes.

Float Steam Traps

Float traps work on the density difference: a float follows the condensate level and opens the valve accordingly, giving continuous discharge. Models with a built-in thermostatic air vent also remove air quickly at start-up.

Advantages: continuous, modulating discharge, high capacity, quiet, resistant to water hammer. Limitations: larger than other types; must be installed horizontally.

Applications: heat exchangers, ovens and cooking kettles, chemical and food plants, laundries.

Inverted Bucket Steam Traps

An inverted bucket inside the body floats when filled with steam and closes the outlet. When condensate arrives, the bucket sinks and opens the outlet. A small vent hole in the bucket lets air and steam escape slowly.

Advantages: robust mechanism tolerant of water hammer and dirty condensate, reliable continuous drainage, usually fails open (equipment does not flood). Limitations: slow air venting at start-up; needs a water seal, which can be lost in superheated steam.

Applications: process equipment and heaters, steam main drainage, older plants with dirty steam.

For condensate in compressed air lines, an air trap (auto drain) is used instead.

See all models on our steam traps page.

Why Choosing the Right Steam Trap Matters

The wrong trap causes energy loss, frequent failures and poor system performance. Consider:

• Operating pressure of the steam line
• Condensate load and flow
• Ambient conditions
• Corrosion risk
• Discharge speed and installation position

For a step-by-step method, read how to choose the right steam trap.

Steam Trap Failure and Testing

A trap that blows steam continuously has failed open and wastes energy. A cold trap, or equipment flooded with condensate upstream, means it has failed closed. For testing methods (visual check, temperature measurement, ultrasonic listening), read how to recognise a steam trap malfunction.