How Steam Ejectors Work
Steam ejectors use steam or gas instead of moving parts to compress a gas. In a jet or ejector, a relatively high-pressure gas, like steam or air, expands through a nozzle. The steam or air converts that pressure or potential energy to velocity or kinetic energy. The jet of high-velocity steam or gas entrains the gas to be evacuated or pumped in the suction of the ejector. The resulting mixture enters the diffuser where velocity energy is converted to pressure at the ejector discharge.
Ejectors that use air as motive are often called air ejectors or air jets. Air is often employed on small ejectors when steam is not available. When paired with a NASH liquid ring vacuum pump, they can use the air from the room or the pump exhaust as motive air to increase the vacuum level the pump is capable of reaching. This is often used in applications such as deaeration when the vacuum system must be able to pull down to the vapor pressure of the water that is being degassed. Air jets of this type are convenient because no steam or pressurized air source is required to make it work, just the vacuum pump.
