Uses and disadvantages of steam traps

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A steam trap is an automatic valve used in steam heating equipment, steam transmission pipelines, and steam-using devices. The condensate water generated by steam power generation is quickly removed from the device, preventing fresh steam from leaking and keeping the efficiency of the device at its optimal level. No steam trap, in any form or type, is universal. To select and install the ideal steam trap, consideration should be given to the structure and type of the steam-using equipment, the operating conditions and purpose, as well as the degree of sealing of the equipment. The key points for selection are mainly explained from the perspective of steam traps below. Terminology for steam traps: Since steam traps differ significantly from ordinary valves in terms of structure and performance parameters, and some of the specialized terms are prone to confusion, the following explains some of the key terms in order to help users understand steam traps better and select them appropriately. Mechanical steam trap: A steam trap driven by changes in condensate temperature. Thermostatic steam trap: A steam trap driven by changes in condensation temperature. Thermodynamic steam-water valve: A steam trap driven by the dynamic properties of steam and condensate water. Maximum allowable pressure: The highest pressure that a steam trap can sustain indefinitely under a given temperature. Maximum operating pressure: The highest pressure at the inlet of the steam trap under proper operating conditions, as specified by the manufacturer. Operating back pressure: The pressure at the outlet of the steam trap under operating conditions. Backpressure ratio: The percentage of the operating backpressure to the operating pressure. Maximum allowable temperature: The highest temperature that the steam trap housing can withstand permanently at a given pressure. Subcooling: The absolute value of the difference between the temperature of the condensate water and the saturated temperature at the corresponding pressure. Condensate drainage capacity: The maximum weight of condensate that a steam trap can drain within 1 hour under given pressure differences and at 20°C. Heat-condensed water discharge volume: The maximum weight of heat-condensed water that a steam trap can discharge within 1 hour under given pressure differences and temperatures. Steam leakage rate: The amount of fresh steam that leaks out of a steam trap per unit of time. No-load steam leakage: The amount of steam that leaks from a steam trap under conditions of fully saturated steam. Load-induced steam leakage rate: The amount of steam leaked by the steam trap at a given load level. No-load steam leakage rate: The percentage of no-load steam leakage relative to the maximum amount of heat-condensed water discharged at the corresponding pressure. Load condition steam leakage rate: The percentage of the steam leakage under load to the actual amount of heat-condensed water discharged during the testing period. Load factor: The percentage of the actual heat condensate discharge during the test period to the maximum heat condensate discharge at the test pressure. Capacity and safety factor of steam traps When selecting steam traps, it is a prerequisite to fully understand the design, purpose, and characteristics of the steam delivery pipes and various heat exchangers and other steam-using equipment that will be used, as well as to accurately determine the capacity of those devices themselves. If the capacity of the steam-using equipment is known, the capacity of the steam trap it requires can also be determined. To determine the capacity of a steam trap, it must be calculated using the following principle: Capacity of the steam-using equipment (amount of condensate generated) × safety factor = capacity of the steam trap. The safety factor is a margin of safety estimated to ensure that the steam trap can function properly even when there is a discrepancy between the actual amount of condensate generated by the steam-using equipment and the capacity specified, when determining the capacity of the steam trap. This safety factor is neither determined purely theoretically and cannot be calculated, nor does it entirely stem from empirical data. Generally speaking, the best way to determine the safety factor is to ask the manufacturer of the steam trap directly. If an inappropriate safety factor is chosen when selecting a steam trap, resulting in either an excessive or insufficient capacity for that trap, it can lead to very serious consequences. If the safety factor is too high, that is, if a steam trap with an excessive capacity is installed, the following disadvantages will arise: a larger capacity of the steam trap increases costs. In the case of steam traps with intermittent operation, an excessive capacity will lengthen the operating cycle of the trap, increase the average retention time of condensate, and reduce the capacity of the steam-using equipment. For steam traps that operate continuously (proportionally), such as float-type steam traps, the small opening degree of the valve disc means that an excessive capacity can cause scuffing on the valve seat. When high-speed fluid passes through a narrow gap, it causes erosion of the contact surfaces, resulting in grooves that damage the valve seat and lead to leakage. It shortens the lifespan of steam trap valves. Conversely, if the safety factor is too low, it will result in the capacity of the used steam trap being insufficient, leading to the following problems: an inability to adapt to changes in the load of the steam-using equipment, which significantly reduces operational efficiency. The condensate passing through the drain valve often reaches its maximum level, causing corrosive damage to the valve disc and seat. It shortens the lifespan of steam trap valves. Therefore, when selecting a steam trap, it is necessary to conduct thorough research on various aspects such as the type and capacity of the trap, while also seeking guidance from the trap manufacturers. Selection of steam traps: When selecting a steam trap, it is necessary to choose the most suitable type based on the type of steam-using equipment and the operating conditions. To this end, it is necessary to properly understand the characteristics and operating conditions of steam-using equipment. When determining the type of steam trap, it is necessary to understand the following items in detail in order to select a steam trap that meets the application requirements. The condensate load of steam-using equipment and the load characteristics of the condensate. Steam conditions: pressure, temperature, saturated steam, or superheated steam. Backpressure conditions: Discharge to the atmosphere or recovery of condensate water (what is the backpressure). Valve body material. Connection type. Safety factor. Others: Corrosivity of condensate water; possibility of water hammer; risk of freezing; any specific requirements regarding noise and environmental pollution; difficulty level of maintenance and inspection, etc. Furthermore, when selecting a steam trap, attention should be paid to the selection criteria for such traps, that is, choosing a type that meets the applicable requirements. Choose a capacity that suits the usage conditions. Choose good durability that meets the usage requirements. Choose products that are easy to maintain.