The right steam trap removes condensate and non-condensable gases without allowing valuable steam to escape. Choosing the wrong trap can contribute to poor heat transfer, water hammer, higher energy use, equipment damage, and increased maintenance.
Steam trap selection should be based on the application, operating pressure, condensate load, temperature, air-venting requirements, installation environment, and maintenance needs. Mechanical, thermodynamic, and thermostatic steam traps each operate differently and are better suited to certain parts of a steam system.
Choose a steam trap by matching its operating principle and discharge characteristics to the application.
Continue below for a comparison of steam trap types and the operating factors that should guide final selection.
A steam trap is an automatic valve that removes condensate and non-condensable gases from a steam system while minimizing the loss of live steam.
Condensate forms as steam releases heat and changes back into water. If condensate is not removed effectively, it can reduce heat transfer, restrict steam flow, contribute to corrosion, and increase the risk of water hammer.
A properly selected steam trap helps:
| Steam Trap Type | How It Operates | Common Applications | Selection Considerations |
|---|---|---|---|
| Mechanical | Responds to the difference in density between steam and condensate. | Steam-using equipment, steam mains, drip service, and high-temperature tracing | Often selected when continuous condensate discharge and rapid response are important. |
| Thermodynamic | Uses the pressure and velocity differences between steam and condensate to open and close a disc. | Steam main drainage, tracing, drip service, and certain high-pressure applications | Compact and durable, but performance can be affected by surrounding temperature and weather conditions. |
| Thermostatic | Opens and closes in response to temperature. | Air venting, tracer lines, and applications where condensate subcooling is acceptable | Effective for air removal and energy conservation, but may allow condensate to remain in the line until it cools. |
The first step is determining where the trap will be installed and what it must accomplish.
Common steam trap applications include:
A trap that works well on a steam distribution line may not be the best choice for process equipment with a rapidly changing condensate load.
The trap must be able to discharge the expected condensate load under actual operating conditions. Selection should account for both normal operation and startup, when condensate loads may be significantly higher.
Consider:
Verify the steam pressure, condensate return pressure, operating temperature, and maximum allowable pressure for the application.
The available differential pressure across the trap affects discharge capacity. A trap should not be selected based only on the upstream steam pressure.
Air and other non-condensable gases can slow startup and reduce heat transfer. Applications that require rapid startup or consistent heating may benefit from a trap with strong air-venting performance.
Thermostatic elements are commonly used for air venting because they remain open while the system is cold and close as steam temperature is reached.
Steam traps may discharge condensate continuously or intermittently.
Installation position, available space, weather exposure, freezing risk, vibration, and access for maintenance can all influence trap selection.
Review:
The trap should be accessible for inspection, testing, cleaning, and replacement. Steam trap selection should also account for the facility’s maintenance capabilities and preferred testing methods.
Standardizing trap types where practical may simplify spare-parts inventory, technician training, and ongoing maintenance.
Mechanical steam traps respond to the difference in density between steam and condensate. A float or bucket moves as condensate enters the trap, opening or closing the discharge valve.
Free Float steam traps are commonly used on steam-using equipment, steam distribution lines, and high-temperature tracing applications.
Potential advantages include:
Inverted bucket traps use an internal bucket that rises and falls in response to steam and condensate.
Selection considerations include:
Thermodynamic disc steam traps use the pressure and velocity characteristics of steam and condensate to control a disc.
They are commonly selected because they are compact and can operate across a wide pressure range.
Common applications include:
Selection considerations include:
Thermostatic steam traps open and close based on temperature. Common designs include bimetallic, balanced-pressure, and expansion-type traps.
They are commonly used for:
Because thermostatic traps may hold condensate until it cools below steam temperature, they are not the best fit for every heat-transfer application.
A steam trap may fail open, fail closed, leak, or operate inconsistently. Common warning signs include:
Higher-than-expected pressure or temperature in the return line may indicate that a trap has failed open and is allowing live steam into the condensate system.
Water hammer may result from condensate accumulation, poor drainage, or steam entering a condensate return line. It can create noise, vibration, piping stress, and equipment damage.
A trap that remains cold during operation may have failed closed or become blocked. This can cause condensate to back up in the steam line or equipment, reducing heat transfer and increasing the risk of water hammer.
A failed-open or leaking trap can waste steam and increase energy consumption without creating an obvious visible leak.
Steam traps are commonly evaluated using ultrasonic testing and temperature measurements.
The TLV TrapMan system can use ultrasonic and temperature readings to help categorize trap condition and estimate leakage.
Steam trap selection is only one part of maintaining an efficient and reliable steam system. Proper sizing, installation, testing, condensate removal, pressure control, and maintenance all affect system performance.
MCE can support steam and flow control applications with:
Need help comparing steam trap types or selecting a trap for a specific application? Contact an MCE flow control specialist to discuss your steam system, operating conditions, and condensate-removal requirements.