Steam jet compressors are preferably used in vacuum process, because large volumes of steam can be efficiently compressed in a single way. This heat pumps used high pressure motive steam. This steam is brought to high velocity by expansion in the motive nozzle and then mixed with the suction steam to be compressed. Some of the kinetic energy is transferred to the suction flow.
In the diffuser the kinetic energy of the mixed flow is converted into pressure energy so that the total steam leaves the jet compressor with a pressure between suction and motive steam.