Jet pump apparatus

A jet pump apparatus for mixing a higher pressure gas from a higher pressure gas supply and a lower pressure gas from a lower pressure gas supply, the apparatus including an inlet section, an outlet section, a diffuser section and a mixing section, the inlet section including a higher pressure gas inlet and a lower pressure gas inlet, the mixing section including a plurality of separated mixing chambers, and the diffuser section including diffusers for receiving mixed gases from each of the mixing chambers, and the outlet section for receiving mixed gases from the diffuser section and conveying the mixed gases to a mixed gas outlet, and the inlet section including a higher pressure gas inlet duct which receives higher pressure gas from the higher pressure gas inlet, and a lower pressure gas inlet duct which receives lower pressure gas from the lower pressure gas inlet, and for each of the plurality of mixing chambers, there being a primary nozzle for introducing primarily higher pressure gas from the higher pressure gas inlet duct axially into a respective mixing chamber, and there being a secondary inlet for introducing primarily lower pressure gas from the lower pressure inlet duct axially into each of the mixing chambers, the higher pressure gas being derived from a compressor section of a gas turbine engine, wherein each of the diffusers of the diffuser section has a cross section which increases towards the outlet section;

• wherein the mixing chambers are each of circular cross section, and the mixing chambers are closely nested so that there is an axially extending spacing between the nested mixing chambers;
• and wherein exterior walls of adjacent diffusers at least at the larger diameter end of the diffuser are in contact.