Steam Traps

What Is a Steam Trap? Function, Operating Principle and Types

A plain-language summary of what a steam trap does in a steam system, why it is needed, and the basic operating principles of mechanical, thermostatic and thermodynamic traps.

ORFA Technical TeamUpdated: Oct 30, 20263 min read

What is a steam trap – steam trap on a steam line

In industrial plants, steam is a powerful energy carrier used for heating, drying, sterilisation and many other processes. As steam gives up its heat it condenses into water, known as condensate. So, what is a steam trap? A steam trap is an automatic valve that discharges condensate and air from a steam system while preventing steam from escaping.

This article explains, at a basic level, what a steam trap does, why it is needed, how it works and the main types.

What Does a Steam Trap Do?

Condensate forms continuously in steam lines and steam-using equipment. If it is not removed, it covers heating surfaces, collects at the bottom of pipes and causes a range of problems. A steam trap discharges this condensate automatically, delivering these benefits:

Energy efficiency: Prevents heating surfaces from waterlogging and stops live steam escaping, so steam energy is used efficiently.
Less corrosion: Condensate combined with air, especially dissolved oxygen and carbon dioxide, accelerates corrosion. Removing condensate and air reduces this risk.
Equipment protection: Prevents condensate from accumulating in equipment and reduces the risk of failure.
Process safety: Reduces the risk of water hammer caused by condensate in the lines being picked up by the steam.

How Does a Steam Trap Work?

Every steam trap has a mechanism that can tell steam and condensate apart. Steam traps fall into three main groups according to the physical property used for this:

Group	Difference it detects	Example types
Mechanical	Density difference between steam and condensate	Float, inverted bucket
Thermostatic	Temperature difference between steam and condensate	Balanced pressure (capsule), bimetallic
Thermodynamic	Difference in flow behaviour (velocity and pressure) of steam and condensate	Disc thermodynamic

Types of Steam Traps

Float steam traps

Condensate collecting in the body lifts the float and opens the discharge valve. They discharge condensate continuously as it forms and are unaffected by sudden and wide pressure changes, making them ideal for temperature-controlled systems.

Thermostatic steam traps

They respond to condensate temperature, opening when condensate cools below saturation temperature and closing when steam arrives. They make some use of the sensible heat in condensate and vent air well.

Thermodynamic steam traps

Incoming condensate lifts the disc and is discharged. As hot condensate passes to the lower-pressure outlet, flash steam forms; its high-velocity flow under the disc lowers the pressure there, while steam filling the chamber above the disc presses it onto the seat and closes the trap. They stand out for their compact, robust construction.

Tip: No single trap type suits every application. Mains drainage, heat exchangers, tracer lines and sterile processes may each need a different type; consider pressure, condensate load and application together when selecting.

Where Are Steam Traps Used?

Drain points and ends of steam mains
Heat exchangers, heater batteries and tanks
Drying cylinders, presses and irons
Tracer lines
Sterilisers and autoclaves

Frequently Asked Questions

What happens without a steam trap?

Condensate builds up on heating surfaces and in pipes; heat transfer falls and the risk of water hammer and corrosion rises. A valve left open to drain condensate would also pass live steam, causing serious energy loss.

Which steam trap type is used most?

There is no single right type. Thermodynamic traps are common for mains drainage, float traps for heat exchangers and thermostatic traps for tracer lines; selection should always be based on the application.

Do steam traps also remove air?

Many do. Thermostatic traps vent air well, and float traps usually include a thermostatic air vent. Where large amounts of air collect, a separate air vent may also be used.

Conclusion

Steam traps are essential components for using steam efficiently and safely. By discharging condensate and air while holding back steam, they save energy, protect equipment and improve process safety. Browse all trap types in our steam traps product group, or ask the ORFA technical team for help choosing the right one.

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