Steam traps are special types of valves which prevent the passage of steam but allow condensate through. It works automatically and is used in steam heating lines to drain condensate without passing any steam. The benefit gained with a steam trap, is that steam is contained in the heating line until it condenses, thus giving up all of its latent heat.

Thermodynamic steam trap use pressure energy of the steam to close the valve which consists of a simple metal disc. The sequence of operation is shown in figure below.

Thermodynamic trap is classified as USMANI VALVES operated traps and it’s the most widely used trap in the oil and gas industry amongst all types. This thermodynamic trap has an extremely robust design and works on a simple mode of operation. It can operate at very high temperature and pressure. The means of operation for the trap is the dynamic effect of steam as it passes through the trap as shown in the sketch 1 below. The disc above the flat face inside the control chamber or cap is the only moving part in the trap.

• The functioning of the thermodynamic trap can be understood from the accompanying sketch above. During the initial startup cold air and Condensate lift the disc from the seat to pass radially outwards through the annular groove to the exit port (refer Figure-1, Sketch 1).
• As the Condensate approaches the accompanying steam temperature it tends to flash giving rise to the velocity of fluid passing under the disc and thereby causing a drop in the pressure. The flashed steam eventually filled in the control chamber, at the same time exerts pressure from above to push the disc down against the seat which snaps the flow passage shut to block the discharge of the condensate (refer Figure-2, Sketch 1).
• The Disc remains closed under the steam pressure of the flash steam of the control chamber for a while (refer Figure-3, Sketch 1).
• With lapse of time the flash steam in the control chamber condenses (by loosing heat to the surrounding atmosphere) to once again lift the disc under the upstream line pressure and allow the flow of Condensate.