The Low volume-high velocity (LVHV) exhaust system is a unique application of exhaust which uses small volumes of air at high velocities to control dust from portable hand tools and machining operations. Control is achieved by exhausting the air directly at the point of dust generation using close-fitting, Custom-made hoods. Capture velocities are relatively high but the exhaust volume is low due to the small distance required. For flexibility, small diameter, light-weight plastic hoses are used with portable tools. This results in very high duct velocities but allows the application of local exhaust ventilation to portable tools which otherwise would require larger flow rates and large dust sizes when controlled by conventional exhaust methods. The resulting additional bene-fit is the reduction of replacement air requirements.
This technique has found a variety of applications although its use is not common. Rock drilling dust has been controlled by using hollow core drill steel with suitable exhaust holes in the drill bits. Air is exhausted either by a multi-stage turbine of the size generally used in industrial vacuum cleaners or, in the case of one manufacturer, by the exhaust air from the pneumatic tool which operates a Venturi to withdraw air from the drill. Some applications use flexible connections to a central vacuum system to aid in the control of graphite dust at conventional machining operations. One-to two-inch diameter flexible hose was used with simple exhaust hoods mounted directly at the cutting tool. In a similar application for the machining of beryllium, a central vacuum system utilizing 1.5-inch I.D. flexible hoses was employed. The exhaust hoods were made of Lucite or transparent material and were tailor-made to surround the cutting tools and much of the work. Exhaust flow rates vary from 120-150 cfm with inlet velocities of 11,000-14,000 fpm. In another application, a portable orbital sanding machine has been fitted with a small exhaust duct surrounding the edge of the plate. A fitting has been provided to connect this to the flexible hose of a standard domestic vacuum cleaner.