Steam Traps – Basic Features, Types & Applications

A steam trap is a control valve whose basic function is to allow condensate to flow, while preventing the passage of steam until it has given up its heat by condensing back to water; in other words, a steam trap is a self-contained valve which automatically drains condensate and discharges air and non-condensable gases from a steam-containing pipe or vessel. This ensures the steam system is able to operate efficiently, without the detrimental effects of unwanted condensate; this is particularly essential in temperature critical applications.

Failure to remove condensate from the steam system may lead to the following problems:

• Damage to the system and process equipment.
• Poor heat transfer.
• Poor quality or wasted product.

Steam traps are employed in a wide range of industries, for instance they are used in: paper mills, textile plants, plant mills, food processors as well as large building complexes with central steam heating systems like hospitals, colleges, and so forth.

Steam Trap Types

Steam traps can be classified into three basic types according to their mode of operation:

Thermodynamic Traps

These are steam traps that are actuated by the principles of thermodynamics and fluid dynamics. They are best suited for steam mains drainage because of their simplicity, robust construction and long life.

Mechanical Traps

These are steam traps that are actuated by a float, responding to changes in condensate level.

Thermostatic Traps

Thermostatic traps are actuated by temperature sensitive devices, responding to changes in condensate temperature. These types of traps are particularly used in applications where you would need to make use of the heat in the condensate such as sterilization. The thermostatic steam trap doesn’t open until the condensate temperature drops below the saturated steam temperature. This allows the heat in the condensate to be utilized before it is drained off, which in turn reduces the flash steam losses and can help to reduce the energy costs.

Let’s consider the following application where steam trap is used with a steam tracing system (i.e. a copper tube carrying low-pressure steam, bundled alongside one or more impulse tubes, enclosed in a thermally insulating jacket) to prevent the impulse lines from freezing:

Steam flows through the shut-off valve, through the tube in the insulated bundle, transferring heat to the impulse tube as it flows past. Cooled steam condenses into water and collects in the steam trap device located at the lowest elevation on the steam trace line. When the water level builds up to a certain level inside the trap, a float-operated valve opens to vent the water. This allows more steam to flow into the tracing tube, keeping the impulse line continually heated.

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