Appliance Design - July 2008 - (Page 28)

MOTORS & PUMPS MOTORS & PUMPS Air and vacuum pumps come in a wide range of sizes, from small to large. Airing the Options Defining air pressure or vacuum needs is key to specifying the right pump. F by david c. droege David C. Droege is OEM Product Specialist at Thomas Products Division, Gardner Denver, Sheboygan, Wis. 28 applianceDESIGN July 2008 or engineers designing pressurized air or vacuum systems, it’s important to understand that no single air-pressure or vacuum technology is optimal for all applications, as illustrated by the comparisons shown in Fig. 1 and Fig. 2. To help narrow down the choices, engineers can peruse charts for flow, pressure, and vacuum that are widely available from pump manufacturers. Before starting the process, however, it is helpful to be acquainted with the chief characteristics of the most common pump technologies used by equipment designers. WOB-L piston: This technology possesses high pressure and vacuum capabilities relative to the compact size and light weight of the unit. It delivers moderate to high air flows, depending on the design, and is very efficient, especially compared with similarly sized diaphragm pumps. The pump is relatively quiet and easily serviceable, and has a dry-running (oil-less) design for very clean output. Modern seal materials and simple design contribute to long, service-free life, especially at lower pressures. The intake air must be filtered and should be generally dry. The pump is not suitable for full-pressure restarts. Rotary vane: This pump has the highest air flow relative to physical size, but is not applicable to high-pressure applications. It can be oil-lubricated or oil-less, and provides the smoothest air flow that is free of pulsation. Its simple design contributes to long life, but it is less efficient than piston or diaphragm pumps. The pump exhibits a characteristic whine, especially in smaller sizes, and its vane debris can contaminate output air. It is not suitable for full-pressure restarts. Articulated piston: This type is generally chosen for heavy industrial applications that require the longest life, especially where fullpressure restart is required. It offers high pressure and vacuum with high flows and can be oil-lubricated or oil-less. The pump’s noise can be an issue, and it is relatively heavy and higher priced. Its intake air must be filtered and dry. Diaphragm: This style works best for lower pressure or moderate vacuum at lower air flows. The design is tolerant of aggressive media, including liquids. It has quiet operation and may have lower pulsation than some piston pumps. The pump is available in many sizes and price points for application flexibility. It has a generally oil-less design for clean air www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - July 2008

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