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• Basics of Steam
• Heating with Steam
• Steam Heat Transfer
• Steam Partial Pressure #1: Why the Temperature Doesn’t Rise
• Steam Partial Pressure #2: Air Removal (Part 1)
• Steam Partial Pressure #3: Air Removal (Part 2)
• Steam Trap Losses - what it costs you
• Types of Steam and Their Applications
• Vapor and Flash Steam
• Various States of Steam
• Steam Trap
• Insulating Traps
• Steam Locking and Air Binding
• Temperature Control Trap Precautions
• The History of Steam Traps #1
• The History of Steam Traps #2
• Trap Back Pressure
• Trap Installation Orientation
• Traps and Orifices Part 1
• Traps and Orifices Part 2
• What is a Steam Trap?
• Condensate Recovery
• Stall Phenomenon #1: Causes & Resulting Problems
• Stall Phenomenon #2: Methods for Preventing Stall
• Piping / Other
• Bypass Valves
• Check Valve Installation and Benefits
• Condensate Recovery Piping
• Pressure Reducing Valves for Steam
• Types of Valves and Their Applications
• Air Trap
• Preventing Clogging of Air Traps
• Removing Condensate from Compressed Air

Vapor and Flash Steam

Difference between vapor and flash steam

Vapor: The diffused reflection of light off the small water droplets of steam in the air appears as a white cloud. In other words, vapor is water in a liquid state floating in the air.

Steam: A colorless transparent gas formed when water in a liquid state is converted into gas through the transfer of the latent heat of steam.

Thinking that vapor = steam is not a problem in normal daily life, but for industries involving the handling of steam, it is very important to make the distinction between the two.

Vapor released from traps

Why is vapor released from traps? If condensate has a higher heat-content than does saturated water at atmospheric pressure, then some of the condensate released from the trap will turn back into steam the moment it hits the atmosphere.

Immediately this condensate-turned-steam (flash steam) condenses in the air, forming tiny water droplets that appear to the eye to be vapor being released from the trap. So though the amount will differ depending upon the discharge temperature, traps discharging hot condensate will always generate some vapor.

OK, but why sometimes lots of vapor?

When large amounts of vapor are seen at the trap outlet, it is sometimes mistakenly thought to be due to steam trap failure or steam leakage. How much flash steam appearing as vapor is actually being released?

An example: If a trap releases 10 kg/h of condensate at 1.0 MPaG to atmosphere, the amount of flash steam generated is roughly 1.6 kg/h. This has a volume of roughly 2.7 m³ (greater than the capacity of 2 large bathtubs). As the flash steam diffuses, it becomes vapor and can understandably lead to the impression that there is a very large quantity of vapor. We must remember that this is from flash steam and not from steam leakage.

Discharge from free float traps on steam mains

What looks like steam leakage even from traps that are operating normally is actually flash steam. The state of condensate and flash steam discharge varies as condensate rates fluctuate.