How does an air ejector work?

• A. Steam passes through the nozzle where velocity increases and pressure decreases, causing suction.
• B. It relies on a mechanical pump to create suction.
• C. It uses electric fans to extract gas.
• D. It uses a vacuum pump powered by electricity.

Answer: (A)

At the heart of an air ejector is the idea that a high-velocity jet of motive fluid can create suction by entraining surrounding gas. When steam (the motive fluid) is forced through a nozzle, it speeds up dramatically. This rapid acceleration lowers the static pressure in and just behind the jet. That lower pressure region draws in the surrounding air or gas, which becomes entrained in the steam jet. The steam carries this entrained gas along, mixing it as it flows down the ejector. The combined stream then passes through a diffuser where its velocity drops and pressure is recovered for discharge. So the suction comes from the momentum transfer of the high-velocity steam to the surrounding gas, not from any mechanical pump or electrical device.

That’s why the option describing steam passing through a nozzle to increase velocity, which lowers pressure and causes suction, is the best choice. It does not rely on a separate mechanical pump, fans, or an electric vacuum pump.