Vacuum pumps mechanically generate a consistent vacuum used in various vehicle systems, most notably diesel engine turbocharger control, brake boosters, and emissions control. Typically engine-driven, these pumps replace or supplement engine intake manifold vacuum lost in modern engine designs. Internal designs utilize rotating vanes, lobes, or pistons to create a sealed chamber and draw vacuum. Output is measured in inches of mercury (in. Hg) or kPa, with capacities varying based on application demands. Many units incorporate check valves to maintain vacuum during pump inactivity and some feature integrated reservoirs for supplemental volume.