Positive-displacement blowers (Fig. 1) are often used to move air ranging in pressures from slighdy negative to about 15 psig (-1 bar) positive. These rotary-lobe machines are typically used for polymer powder or pellet transfer and come in different sizes. A number of models with 10-, 12- and 14-in. shaft center to shaft centers are among the most widely used versions. Drives for these blowers include direct-connected motors as well as a number of gearbox and belt arrangements. Many positive-displacement blowers are oil-splash lubricated, while some of the larger ones are forced-feed lubricated.
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