What are the types of traps?

　The proper name for a steam trap is a hydrostatic drain; it is also known as an automatic drain or condensate discharge device. These devices are classified into those used in steam systems and those used in gas systems. Mechanical steam traps (free-floating ball type, lever-ball type, inverted bucket type) operate on the principle of buoyancy. It can automatically distinguish between steam and water, and is commonly used in applications that require continuous drainage, involve large flow rates, and where the drained water needs to be collected for reuse. Among them, lever float type steam traps and inverted bucket type steam traps have complex structures, while the free float type steam trap has a simple structure and does not allow steam leakage; it is generally used for pipeline steam drainage or equipment steam drainage ； Thermodynamic (disk-type, pulse-type) traps utilize aerodynamic principles, with the pressure drop generated by the redirection of gas being used to open and close the valves. Used in applications with low flow rates, high differential pressures, and low requirements for continuity; it has a simple structure and suffers from pulsative leakage, and is generally used for pipeline drainage ； 　　Thermostatic traps (bimetallic, diaphragm, and bellows types) utilize the difference in temperature between steam and water to activate temperature-sensitive elements, thereby controlling the valve. It has low sensitivity, exhibits lag, and cannot function properly in pipes with pressure changes. It can be installed at the top of steam-using equipment solely for air exhaust; in terms of water drainage, it is commonly used for draining water from heat tracing pipelines ； 　　Pump-valve type traps feature a built-in pump and valve design, and are usually equipped with electric actuators. When draining water, there is no need to consider the pressure difference on either side of the trap, thereby enabling it to drain water from low pressure to high pressure. 　　Most steam traps can automatically identify steam and water (excluding thermostatic types), thereby achieving automatic steam prevention and water drainage. Driers are widely used in industries such as petrochemicals, food and pharmaceuticals, and power plants, playing a significant role in energy conservation and emission reduction. 　　When selecting a steam trap, it is not possible to choose it based on its nominal pressure, as the nominal pressure merely indicates the pressure level that the trap’s housing can withstand; there is often a significant difference between the nominal pressure of a steam trap and its operating pressure. Therefore, the drainage capacity of the steam trap should be selected based on the working pressure difference. The operating pressure difference refers to the difference between the operating pressure before the steam trap and the back pressure at the outlet of the steam trap. The back pressure behind the steam trap is calculated as follows: (when the condensate behind the steam trap is discharged into the atmosphere, the outlet back pressure of the steam trap is zero.) If the condensate discharged by the steam trap is collected together, the back pressure at the outlet of the steam trap becomes the sum of the resistance in the return pipe, the elevation height of the return pipe, and the pressure inside the secondary evaporator (return water tank). ） 　　

Thank you so much, moderator! That’s very comprehensive! I’ve learned it!

Thank you. Is there a schematic diagram?

The thermal dynamic and float-type steam traps that we have come into contact with in our projects

This post was last edited by mba_niu on 2013-7-26 09:25. See pages 361 and 166 of Professor Song Keké’s book \"Pressure Pipeline Design and Engineering Examples, Second Edition\". See page 458 of Professor Lu Peiwen’s “Valve Selection Manual”. There are diagrams, explanations of the principles, and examples of layouts; it’s explained very clearly. There are 4 types of mechanical steam traps that are commonly used, 3 types of thermostatic steam traps that are commonly used, and 2 types of thermodynamic steam traps that are commonly used. Each type has its own advantages and disadvantages, and the choice depends on the specific operating conditions.