of a primary high-vacuum (HV) ejector and a secondary low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure. In operation a three-stage system consists of a primary booster, a secondary high-vacuum (HV) ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull vacuum to the lower intermediate pressure. Finally the booster is operated (in conjunction with the HV & LV ejectors) to pull vacuum to the required pressure. Construction materials Injectors or ejectors are made of carbon steel, stainless steel, brass, titanium, PTFE, carbon, and other materials. See also Aspirator (pump) De Laval nozzle Diffusion pump Giovanni Battista Venturi Gustaf de Laval Nozzle Surface condenser Venturi effect References Further reading External links Use of Eductor for Lifting Water Chemical equipment Fluid dynamics Pumps Locomotive parts Steam locomotive technologies