In short, good condition traps can operate normally but still appear to be leaking steam because the vapor cloud often seen at the outlet of a trap is caused by the flash evaporation of condensate (flash steam).

Visual Example of Properly Discharging Trap Discharge from Free Float® traps on a Steam Main It's important to remember that this is not steam leakage, but condensate that has flash evaporated. As the flash steam diffuses, it turns into a vapor cloud, which can appear to be large in volume. This has a volume of roughly 2.7 m 3 (greater than the capacity of 2 large bathtubs). If a trap releases 10 kg/h of condensate at 1.0 MPaG to atmosphere, the amount of flash steam generated is about 1.6 kg/h. Condensate formed at higher pressure has a corresponding higher temperature, which creates a higher % of Flash and results in greater amounts of visible vapor. How Much Vapor Is Too Much?įlash steam vapor can appear to be a larger amount than it actually is because the difference in specific volume of flash steam compared to condensate may be over 1,500 times greater.

On the other hand, with flash steam, typically only a small percentage by mass of the high pressure condensate flashes into steam due to the exit pressure drop. The appearance of flash steam (by velocity and force) differs from live steam because when a trap is leaking live steam, the majority of the fluid exiting the trap is typically high pressure steam, which is invisible. Because of the pressure difference between the trap inlet and outlet, traps discharging hot condensate will always generate some flash steam. The vapor clouds at the outlet of traps appear when this flash evaporated steam (flash steam) condenses in the air to form tiny water droplets. Condensate discharged out of the orifice of a trap partially evaporates (flash evaporation) due to the pressure difference (illustration).

Steam coming out on top