Steam ejectors (also known as Ejectors, Eductors, Jet Pumps, Velocity Spools or simply SJP's) are devices that use the energy from a high-pressure fluid to boost the pressure of a low-pressure fluid to an intermediate level, and may be used to boost the pressure of liquids, gases or multi-phase flows.
In all cases a stream of fluid from a high pressure source, often called the "HP" or "motive" flow is discharged into a small volume, or vessel, that is connected to a low pressure supply, or reservoir, of fluid. This HP stream is not just fired into the vessel from a side connection, but rather is introduced via a penetrating nozzle and directed, in a very precise and optimised way, at the outlet nozzle within which there is a venturi tube in order to induce flow from the LP piping.
It is the pressure let down of this HP flow, and subsequent mixing of the HP and LP streams, that will generate high noise levels, often in the region of 90 to 100 dB(A), but in the very worst cases up to 115 dB(A).