A steam trap's most important job is to quickly discharge condensate that has formed in steam distribution lines, steam tracers, and in steam-using equipment. A steam trap must also be able to save energy by preventing steam leaks and by discharging non-condensing gases such as air.
Steam traps are classified into different categories based on their construction and operation principles, and there are several different models of steam traps. Consult the links below to narrow down your choices and find the steam trap that best suits your purposes.
1. How Application Affects Selection
2. Safety Factor and Life Cycle Cost
Detailed information on choosing steam traps is provided on the pages linked above, so those details will be omitted on this page. This page explains the type of applications that each variety of steam trap is suited for to inform your choice of trap.
Three Categories of Steam Trap Based on Operation Principles
Each model of steam trap has its own characteristics, and differences in traps' operating processes directly relate to whether or not they are suitable for a particular application. Steam traps can be divided into three different types based on their operating principles:
Mechanical Steam Traps
Mechanical steam traps (also referred to as “density traps”) include Free Float®, lever float, and inverted bucket steam traps. Mechanical traps operate by utilizing the difference in density between steam (or air) and condensate.
For more information on how mechanical traps work, consult the following article:
How Mechanical Traps Work: A Look at their Mechanism and Merits
Thermodynamic Steam Traps
There are two varieties of thermodynamic steam trap: the thermodynamic disc and piston types. Thermodynamic steam traps operate by utilizing the difference in kinetic energy between high velocity steam (a gas) and slower moving condensate (a liquid).
For more information on disc traps, consult the following article:
How Disc Traps Work: A Look at their Mechanism and Merits
Thermostatic Steam Traps
These include bi-metal, balanced pressure, and expansion thermostatic traps. Thermostatic traps operate by utilizing the difference in temperature between condensate that is close to steam temperature and sub-cooled condensate (or low temperature air).
For more information on how bi-metal type thermostatic traps work, consult the following article:
How Bimetal-Type Thermostatic Steam Traps Work: A Look at their Mechanisms and Merit
Applications of Each Type of Steam Trap
Applications Suited to the Free Float® Type
Free Float® steam traps are typically the first choice for removal of condensate from steam-using equipment, steam distribution lines, and high temperature tracing applications.
A Free Float® steam trap can immediately discharge condensate when it enters the trap body, thus preventing condensate build-up and reducing the risk of water hammer in the steam distribution line. These traps increase the operating efficiency of the equipment by enabling steam to contact all of the heat transfer surface area. Additionally, Free Float® traps are highly energy-efficient because the valve discharge orifice is covered by a constant water seal, which prevents steam from leaking out of the trap body.
In contrast, inverted bucket type traps typically include an internal weep hole to bleed off steam (or air) continuously and with each cycle. The weep hole is usually small enough to prevent significant steam loss, but it removes only a limited amount of air, which can hinder system start-up or heat transfer on equipment. Additionally, the intermittent action of the inverted bucket trap makes it typically respond slower than the Free Float®, which operates immediately due to its self-contained buoyancy over water.
Unlike Free Float® steam traps, which are designed for the float ball to rise completely out of the path of flow through its orifice, lever float traps typically pull their valve head back from the seat. Flashing condensate passing through the orifice may pull the valve head towards the seat, reducing the lever float trap’s flow or causing intermittent flow. For these reasons, the Free Float® is the most advanced design of mechanical steam trap.
Free Float® and lever float steam traps are the only types of trap that constantly contain both steam and condensate in the body. Since steam is always present, these models are suitable for service in freezing conditions, provided that the discharge drains to atmosphere and that the body does not deform from freezing. Conversely, inverted bucket traps must maintain a suitable water seal at the bottom of the bucket, and so these types can be prone to freezing damage.
