raise fuel from the main tank to a small auxiliary tank, from which it flows by gravity to the carburetor. This eliminated the fuel pump which, in early cars, was an unreliable item. 1960–1990 Automotive vacuum systems reached their height of use between the 1960s and 1980s. During this time a huge variety of vacuum switches, delay valves and accessory devices were created. As an example, a 1967 Ford Thunderbird used vacuum for: Vacuum-assist brake servos (power brakes) use atmospheric pressure pressing against the engine manifold vacuum to increase pressure on the brakes. Since braking is nearly always accompanied by the closing of the throttle and associated high manifold vacuum, this system is simple and almost foolproof. Vacuum tanks were installed on trailers to control their integrated braking systems. Transmission shift control Doors for the hidden headlamps Remote trunk latch release Power door locks HVAC air routing - Vehicle HVAC systems used manifold vacuum to drive actuators controlling airflow and temperature. Control of the heater core valve Rear cabin vent control Tilt-away steering wheel release Other items that can be powered by vacuum include: Exhaust gas recirculation solenoid Power steering pump Fuel pressure regulator Modern usage Modern cars have a minimal amount of accessories that use vacuum. Many accessories previously driven by vacuum have been replaced by electronic accessories. Some modern accessories that sometimes use vacuum include: Vacuum-assist brake servos Positive crankcase ventilation valve Charcoal canister HVAC air routing Manifold vacuum in diesel engines Many diesel engines do not have butterfly valve throttles. The manifold is connected directly to the air intake and the only suction created is that caused by the descending piston with no venturi to increase it, and the engine power is controlled by varying the amount of fuel that is injected into the cylinder by a fuel injection system. This assists in making diesels much more efficient than petrol engines. If vacuum is required (vehicles that can be fitted with both petrol and diesel engines often have systems requiring it), a butterfly valve connected to the throttle can be fitted to the manifold. This reduces efficiency and is still not as effective as it is not connected to a venturi. Since low-pressure is only created on the overrun (such as when descending hills with a closed throttle), not over a wide range of situations as in a petrol engine, a vacuum tank is fitted. Most diesel