coating, milking machines and other equipment in dairy sheds; vacuum impregnation of porous products such as wood or electric motor windings; air conditioning service (removing all contaminants from the system before charging with refrigerant); trash compactor; vacuum engineering; sewage systems (see EN1091:1997 standards); freeze drying; and fusion research. In the field of oil regeneration and re-refining, vacuum pumps create a low vacuum for oil dehydration and a high vacuum for oil purification. A vacuum may be used to power, or provide assistance to mechanical devices. In hybrid and diesel engine motor vehicles, a pump fitted on the engine (usually on the camshaft) is used to produce a vacuum. In petrol engines, instead, the vacuum is typically obtained as a side-effect of the operation of the engine and the flow restriction created by the throttle plate but may be also supplemented by an electrically operated vacuum pump to boost braking assistance or improve fuel consumption. This vacuum may then be used to power the following motor vehicle components: vacuum servo booster for the hydraulic brakes, motors that move dampers in the ventilation system, throttle driver in the cruise control servomechanism, door locks or trunk releases. In an aircraft, the vacuum source is often used to power gyroscopes in the various flight instruments. To prevent the complete loss of instrumentation in the event of an electrical failure, the instrument panel is deliberately designed with certain instruments powered by electricity and other instruments powered by the vacuum source. Depending on the application, some vacuum pumps may either be electrically driven (using electric current) or pneumatically-driven (using air pressure), or powered and actuated by other means. Hazards Old vacuum-pump oils that were produced before circa 1980 often contain a mixture of several different dangerous polychlorinated biphenyls (PCBs), which are highly toxic, carcinogenic, persistent organic pollutants. See also An Experiment on a Bird in the Air Pump Vacuum sewerage References External links Pumps Pumps Pumps 1642 introductions Gas technologies German inventions 17th-century inventions