Upright vacuum cleaners take the form of a cleaning head, onto which a handle and bag are attached. Upright designs usually employ a rotating brushroll or beater bar, which removes dirt through a combination of sweeping and vibration. There are two types of upright vacuums; dirty-fan/direct air, or clean-fan/indirect air.The older of the two designs, dirty-fan cleaners have a large impeller (fan) mounted close to the suction opening, through which the dirt passes directly, before being blown into a bag. The motor is often cooled by a separate cooling fan. Due to their large-bladed fans, and comparatively-short airpaths, dirty-air cleaners create a very efficient airflow from a low amount of power, and make great carpet cleaners. Their 'above-floor' cleaning power is less efficient, since the airflow is lost when it passes through a long hose.Clean-fan uprights have their motor mounted after the bag. Dust is removed from the airstream by the bag, and usually a filter, before it passes through the fan. The fans are smaller, and are usually a combination of several moving and stationary turbines working in sequence to boost power. The motor is cooled by the airstream passing through it. Clean-air vacuums are good for both carpet and above-floor cleaning, since their suction does not significantly diminish over the distance of a hose, as it does in dirty-fan cleaners. However, their air-paths are much less efficient, and can require more than twice as much power than dirty-fan cleaners to achieve the same results.The most common upright vacuum cleaners use a drive-belt powered by the suction motor to rotate the brush-roll. However, a less common design of dual motor upright, often found in commercial vacuum cleaners, is available. In these cleaners, the suction is provided via a large motor, while the brush-roll is powered by a separate, smaller motor, which does not create any suction. The brush-roll motor can sometimes be switched off, so hard floors can be cleaned without the brush-roll scattering the dirt. It may also have an automatic cut-out feature, which shuts the motor off if the brush-roll becomes jammed, protecting it from damage.