The principle of a rotary, positive displacement blower is, as the drive shaft is rotated, the impellers turn in opposite directions with very finite clearances between each other and between the rotors and the casing. As each impeller passes the inlet, a measured quantity of air is trapped between the impellers and the casing. As the shafts continue to rotate, this “pocket” of air is transported around the casing to the discharge side of the machine, where it is then expelled through the port, against the pressure prevailing in the discharge line. When this occurs, a back flow of air into the “pocket” from the higher-pressure discharge line produces a constant volume pressure rise, causing a pressure pulse resulting in noise. As a “pocket” of air is expelled four times with each revolution of the drive shaft, or twice with each impeller, the fundamental frequency of the pressure pulse is four times the shaft speed. While most applications for rotary positive displacement blowers involve handling air, the machine also is capable of handling any number of gases, from hydrogen to steam to natural gas to ethylene or, of course, nitrogen. Proper attention must be given to seals as well as performance calculations and limitations, all of which will be discussed later. In addition, they perform very well under vacuum conditions as well as pressure.
Because of such a wide variety of products for every application, not all products are listed above, with new ones coming out every day. Please contact 1st Quality Air Inc., your compressed air experts for proper application.
