Steam & Condensate Introduction
WHY ARE STEAM TRAPS REQUIRED? The purpose of the steam trap is to allow Condensate (water that is formed from the condensed steam) and air, to be discharged from the steam system while preventing the loss of live steam. The steam trap is a special type of valve which opens when condensate and air are present and closes when steam tries to pass. CONDENSATE: (condensed steam or water): Any time steam releases its heat energy (latent heat), the steam condenses back to water. This water is therefore referred to as condensate. This transformation of steam back to liquid condensate will occur in a radiator heating a room, in a heat exchanger making hot water, in a pipe transferring the steam over long distances, or in any process that uses steam. If this condensate is not continuously removed, the radiators, heat exchangers and piping will fill with condensate (water). The removal of condensate from the steam system, while preventing the loss of live steam, is therefore the primary function of the steam trap. AIR: Before the steam is turned on and the system is cold, air will exist in all the steam pipes and process equipment, such as radiators and heat exchangers. This air must be bled from the entire system to allow the steam to enter and reach its intended designated process. The air is actually pushed thru the system by the incoming steam and automatically bled thru the process traps at the end of the steam lines or special air vents at the high points in the system. This bleeding of air from the system allows the steam to enter. GENERAL APPLICATION CATEGORIES for STEAM TRAPS: DRIP APPLICATIONS: Drip applications refer to removing the condensate that forms in the steam main and steam supply lines as opposed to condensate that forms at the actual process (heat exchanger, jacketed kettle, radiator, etc.). When steam loses its heat energy due to radiation losses through the pipe walls, condensate forms in the pipes. This condensate needs to be continuously removed, and it is therefore common to have steam traps placed 150–300 feet apart throughout the piping system. Traps used for this application are referred to as drip traps and have small condensate capacities as opposed to process traps. Drip traps are not normally relied upon to discharge the air from the system. Air removal is performed by the process traps and air vents located throughout the system. The most common trap choices for drip applications are the Thermodynamic style for line pressures over 30 PSIG, and Float & Thermostatic style for line pressures up to 30 PSIG. Inverted Bucket (IB) style traps are also commonly used for drip trap applications. The orifice of the IB is mounted at the top of the trap which makes them less susceptible to failure from dirt and pipe scale when compared to other trap types. PROCESS APPLICATIONS: Process applications refer to removing condensate and air where the actual process using the steam is taking place. This process could be a heat exchanger making hot water, or a radiator heating a room, or anything else that requires the use of steam. Traps used for process applications require larger condensate handling capability in contrast to steam traps that are used for drip applications. Traps used in Process applications also need to be able to discharge large amounts of air present in the system at start-up. The most common trap choice for process applications are Float & Thermostatic traps since they do an excellent job of discharging condensate and air. Thermostatic traps make a good choice for process applications since they also do an excellent job of discharging air and condensate. In contrast, the lack of air venting capability of the Thermodynamic and Inverted Bucket traps, make these trap types a less desirable choice for most process applications.
Common Types of Steam Traps
Shown below are some of the most common types of steam traps; Float and Thermostatic, Thermodynamic, Thermostatic, as well as a Thermostatic Air vent. Other common steam trap types are the Inverted Bucket and the Bi-Metal. In the following diagrams, other system components such as control valves and regulating valves are often required to control steam pressure and process temperatures. (Some piping components may not be included in the diagrams for simplification purposes.)
Thermostatic Trap Thermodynamic Trap Float &Thermostatic Trap Thermostatic Air Vent
Contains a float-operated valve to discharge condensate, and a thermostatic air vent which discharges air, but will close when steam is present.
Contains a thermostatic element which allows air and condensate to be discharged, but closes when steam is present.
Contains a disc and seat arrangement which allows condensate to be discharged, but will close when steam tries to pass through.
Air Vents are used in steam systems for the removal of air and other non- condensable gases. They are placed at the end of steam mains and directly on process equipment.
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