Figure 16-45.  A turbocharger installation on a reciprocating aircraft engine (top left side).  Figure 16-46.  roots blower found on older pressurized aircraft is gear driven by the engine. It pressurizes air as the rotors rotate very  close to each other without touching.  pressurized. Due to the low pressure establi shed in the  venturi by the bleed air flow, air is drawn in from outside  the aircraft. It mixes with the bleed air and is delivered to the  pressure vessel to pressurize it. An advantage of this type of  pressurization is the lack of moving parts.  [Figure 16-48]  A  disadvantage is only a relatively small volume of space can  be pressurized in this manner. Another method of pressurizing an aircraft using turbine  engine compressor bleed air is to have the bleed air drive a  separate compressor that has an ambient air intake. A turbine  turned by bleed air rotates a compressor impellor mounted  on the same shaft. Outside air is drawn in and compressed.  It is mixed with the bleed air outflow from the turbine and  is sent to the pressure vessel. Turboprop aircraft often use  this device, known as a turbocompressor.  [Figure 16-49] 16-27 The turbocharger incorporates a turbine,  which is driven by exhaust gases, and a compressor that pressurizes the incoming air. TURBOCHARGER Drive end cover Driving gear Rotor case Air inlet port Driving rotors Adjusting ring Extractor seal shell Rotary shell Extractor scroll Stub shaft Driving gear Ball bearing Abutrnent collar Simplified detail  of blower assembly