Guidelines for Typical Process Applications
Depending on the application, a process steam trap will probably have to handle heavy startup loads, often followed by smaller running loads. The trap's function is to drain the process equipment and thus ensure that effective heat transfer is achieved(through latent heat). A few guidelines for optimum results include:
- Provide an adequate size process connection from equipment;
- Locate trap below the equipment (water runs downhill);
- Use good piping practice to ensure that clean condensate is presented to the trap;
- Include air vents and vacuum breakers as necessary for effective equipment operation.
Why Choose a Thermostatic Steam Trap?
Thermostatic traps react to changes in temperature and therefore discriminate very well between steam and cooler noncondensible gases. They can rapidly purge air from a system, especially on cold startups. These traps can be installed in various positions to match piping. Most commonly, actuation is by means of a bimetallic element or a bellows-like capsule filled with a vaporizing liquid. Thermostatic traps respond more slowly to changing conditions due to the heat energy of the condensate inside the trap which is slow to dissipate, thus causing some time delay. Insulating thermostatic traps aggravates this situation. To improve responsiveness, these traps should be mounted at the end of a cooling leg in an area where air can circulate freely and a distance from the collection pocket to match condensate load.
Profile of a Process Application-Gravity Drainage, Shell and Tube Heat Exchanger
Tubes, coils or jackets are used with heat exchangers, tanks or vats for heating liquids in either batch or continuous operation, typical of shell and tube heaters. Equipment is generally protected from the weather and typically features a single coil. Heavy startup loads, followed by smaller running loads are to be expected, but without the extreme swings of weather-exposed equipment. Adequate air venting is most important as the equipment is often run on daily or weekly schedules. Tendency is for total shutdown of equipment following completion of run or batch. Lack of proper venting can cause condensate to be drawn back into the heat exchanger coils. Air in a heating system significantly reduces its efficiency. Air is a very poor conductor of heat and air filming on pipes and heat exchanger tubes reduces the heat transfer rate through their metal walls. Also, steam mixed with air contains fewer BTUs at a given pressure than steam alone. It is the function of a steam trap to aid in venting air from a steam system, but auxiliary thermostatic air vents are often required. Open to cooler air and closed to hotter steam they greatly speed up the air purging process. When frequent startups and shutdowns are the rule, rapid air purging is a significant factor. Thermostatic traps are often favored for their good air handling characteristics on startup.
Pilot Operated Traps
As the name implies, these traps are actuated by a thermostatic pilot valve which drives the main valve. The pilot, which can either be bimetallic or bellows actuated, is in essence a working mechanism similar to that used in bimetallic or bellows traps respectively. Therefore the operating characteristics of pilot operated traps are basically the same as those of the pilot. Pilot operated traps are process traps that offer a dual capacity range. Small condensate loads are handled by the pilot and when the load exceeds its capacity, the main valve opens. An additional advantage of these traps is that they are relatively small in size and lightweight, yet can handle large quantities of condensate. They are a practical alternative to large heavy mechanical traps. Yarway pilot operated traps offer the following advantages:
- Simple construction
- Small size and weight
- Easy to maintain as installed
- Excellent air handling capability
- Energy efficient
Bellows Technology
Yarway offers two bellows technology products for process applications utilizing the FTE (Filled Thermal Element):
- Series 151 Dual Range Steam Trap
- Series AV-5 Thermostatic Air Vent
With the Series 151 trap, the FTE acts as the pilot. This means that by opening or closing its internal valve ?as the condensate temperature changes ?the pilot determines whether the main valve is open or closed. If the condensate load is very low, then the total flow is passed through the pilot only. With the AV-5 Air Vent, the FTE thermostatic bellows opens and closes in response to temperature changes. Steam is prevented from discharging through the vent and only air and subcooled noncondensible or cool condensate can therefore be discharged. All Yarway bellows traps deliver consistent features such as:
- Three-year warranty
- Pressure assisted fail-open design
- Hardened stainless steel valve and seat.
- Withstands superheat
- Efficient air and noncondensible removal
- Shuts tight on steam
- Compact and lightweight
Bimetallic
Yarway offers two bimetallic thermostatic steam traps for process applications:
Bimetallic traps utilize the sensible heat in the condensate in conjunction with line pressure to open and close a valve mechanism. The bimetallic elements are usually in the form of small discs which are arranged to produce an increasing closing force with increasing temperature. This closing force is opposed by line pressure. Since the line pressure is a major force balancing component, this balance is also affected by back pressure. Back pressure in a closed return system provides an additional closing force which, since it opposes the supply pressure, produces a lower opening temperature than the same trap discharging to atmosphere.
Bimetallic steam traps offer the following advantages:
- Ruggedly designed to withstand water hammer
- Energy efficient
- Self-draining
- Resistant to freeze damage
- Capable of temperature adjustment
- Can be mounted in any position
- Primary fail mode is open
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