It eventually reinvented itself as a maker of vacuums and steam cleaners. They are essentially small canister vacuums strapped onto the user's back. In June, 2008, Dirt Devil introduced a line of cordless handheld vacuums with AccuCharge Technology. Specialized shop vacuums can be used to suck up both dust and liquids. Positive displacement pumps are the most effective for low vacuums. PowerBot robotic vacuums by Samsung have also been sold on Amazon.com since 2014. Kirby's vacuums made until 1919 were made by Frantz Premier. Some oils and greases will boil off in extreme vacuums. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. In 1906 James B. Kirby developed his first of many vacuums called the "Domestic Cyclone". In practice, RHEED systems are operated under ultra high vacuums. This is commonly done by industrial vacuums that suck up all the sediment. But higher-quality vacuums are possible. Mercury, as a housewife, vacuums the floor and sings the first verse. Filterless central vacuums are completely immune to such failures.