SPIRAX SARCO TSS 21 STEAM TRAP PMO 21BAR TMO 242◦C TMA 400 C 13:40

The string “PMO 21BAR TMO 242◦C TMA 400 C” describes the trap’s critical pressure and temperature ratings:

• PMO 21 BAR: Pressure Maximum Operating. The trap can continuously operate at pressures up to 21 bar(g) (approximately 300 psig).

• TMO 242°C: Temperature Maximum Operating. The maximum temperature of the medium (saturated steam) the trap can handle is 242°C. This correlates directly with the PMO of 21 bar, as 242°C is the saturation temperature of steam at that pressure.

• TMA 400°C: Temperature Maximum Admissible. This is the highest body temperature the trap can withstand, for example, during a superheat condition or a system heat-up. This is a very high rating, indicating a robust design suitable for demanding applications.

Key Features & Operational Principle

1. Working Principle: It operates on the thermodynamic principle. A single circular disc is controlled by the dynamic forces of steam and condensate.

   • On Start-up: Cold condensate and air lift the disc off its seat and are discharged freely.

   • When Steam Reaches the Trap: The high velocity of steam flowing under the disc creates a low-pressure area, drawing the disc down onto the seat. At the same time, steam pressure acts on the top of the disc, creating a sealing force. The trap closes.

   • Cycling: The trap remains closed until the pressure above the disc drops (as it cools and condenses), allowing the disc to lift and discharge the accumulated condensate. The cycle then repeats.

2. Compact and Lightweight: Its simple design has only one moving part (the disc), making it small, lightweight, and easy to install.

3. All-Stainless Steel Construction: The TSS 21 is typically made entirely of stainless steel, providing excellent resistance to corrosion, water hammer, and freezing.

4. Good Air Handling: It can purge air effectively on start-up, though it is not as efficient as a dedicated air vent under steady-state conditions.

5. Energy Efficient: When working correctly, it is a tight-shutting trap, minimizing live steam loss.

Typical Applications

The TSS 21 is a general-purpose trap suitable for a wide variety of applications, including:

• Steam Mains Drip Legs: A very common and suitable application.

• Shell and Tube Heat Exchangers

• Autoclaves

• Cylinder Dryers

• Process Air Heaters

• Tracer Lines (shorter lines)