Disc steam traps are in the thermodynamic trap category that are actuated by the principles of thermodynamics and fluid dynamics.

Thermodynamic steam traps are phase detectors in that they can discriminate between liquids and gases, but they do not discriminate between steam and air or other non-condensable gases. Therefore, they have a reduced ability to bleed-off those gases. Small amounts of steam may also be passed.

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Disc steam traps utilize the heat energy in hot condensate and the kinetic energy in steam to open and close a valve disc. They are phase detectors, sensing the difference between liquid and gas or vapor. Disc steam trap is very lightweight and compact and contains only one moving part, the disc itself, these small devices are rugged.

During initial start-up, pressure created by cold condensate pushes the valve disc off the seating surface. This uncovers the inlet and outlet ports allowing discharge. As condensate reaches the inlet port (a restriction), it experiences a decrease in pressure and an increase in velocity (in accordance with the laws of fluid dynamics). If the condensate is very close to steam temperature, the lower pressure will cause it to flash into steam (in accordance with the laws of thermodynamics). The resulting high velocity flow beneath the disc, with its attendant localized pressure reduction under the disc, causes it to snap shut. Flow through the trap then stops until the pressure in the chamber over the disc decays sufficiently to allow the inlet pressure to force the disc off its seat. Condensate then flows through the trap until once again it reaches such a velocity and lowering of pressure that flashing occurs and the disc can snap shut. This cycle continuously repeats itself; the disc opening to allow the flow of condensate, and closing on high velocity flash steam.

Disc traps are most frequently used in light condensate load applications and are known as "hot" traps, i.e., quickly discharging very hot condensate immediately after it forms. The disc steam trap is very useful in many applications where space is limited. Because of its simple design and small size, disc steam trap offers advantages such as resistance to hydraulic shock, the complete discharge of all condensate when open and intermittent operation for a steady purging action.

Prior to selecting a steam trap for your application, review steam traps selection with its advantages versus disadvantages and additional steam trap types: Piston Steam Traps, Lever Steam Traps, Closed Float Steam Traps, Inverted Bucket Steam Traps, Open Bucket Steam Traps, Bimetallic Steam Traps, Bellows Steam Traps, Liquid or Solid Expansion Steam Traps (Wax Capsule Steam Trap), and Orifice Steam Traps.