Steam within a heat exchange device is impacted by the presence of condensate and air in the same space, which causes the energy transfer of heat to become less efficient. A steam trap is an automated device designed to remove condensate from a steam-containing enclosure while retaining live steam at the same time, giving the live steam more surface to maximize heat transfer efficiency.
By removing condensate, steam traps allow it to be collected and re-used. This function helps reduce fuel costs, reduce costs associated with fresh water and water treatment requirements, and increases energy savings by reducing the energy lost from the boiler during the blowdown process.
Depending on the size of steam plant and amount of boilers and heat exchange related auxiliary equipment, a system can contain dozens of steam traps which operate based on temperature, density or velocity. Primary designs include thermostatic steam traps, thermodynamic steam traps, ball float steam traps and inverted bucket steam traps.
Thermodynamic steam traps (also called disk traps)
How it works: Condensate and air enter the trap, causing pressure which raises a disc and allows them to be quickly discharged. Steam or flash steam flowing through the trap increases velocity and pulls the disk closed. Condensation of the flash steam decreases chamber pressure causing the disc to open. The cycle is repeated and regulates the cycling rate.
Thermodynamic steam traps are offer simple operation and can be used with high pressure and superheated steam applications over a wide range of operating pressures.
Thermostatic steam traps
How it works: A temperature sensitive element (bellows or bimetallic strip) expands and contracts due a difference in temperature to open and close a valve which releases condensate and air.
A thermostatic steam trap will not open until the condensate temperature drops below saturated steam temperature. Condensate heat can be used before it is drained which can reduce energy costs.
Ball float steam traps
How it works: As condensate enters the trap, a float raises and opens the main valve. Arriving steam then closes the valve preventing the passage of live steam. The steam condenses, causing the float to rise and allowing condensate to be released. As the unit drains, the ball drops and the valve closes.
Inverted bucket steam traps
How it works: Steam enters the trap below an inverted bucket which is submerged. This steam gives buoyancy, causing the bucket to float and close a discharge valve. Condensate entering the trap formed by radiant heat loss causes the bucket to lose buoyancy and sink, opening the trap valve to discharge condensate.
Ball float and inverted bucket steam traps are classified as mechanical by design, used in process applications requiring immediate condensate removal or those where temperature fluctuations are undesirable or problematic.