Chapter 17. -COMPRESSED AIR PLANTS 



SOLENOID 



EXHAUST 



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Figure 17-10. 



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on centrifugal principles; most accurately, 

 perhaps, it might be called a rotary- centrifugal 

 compressor. ~ 



The rotary-centrifugal compressor is used to 

 supply low pressure compressed air. Because 

 this compressor is capable of supplying air that 

 is completely free of oil, it is often used as the 

 compressor for pneumatic control systems and 

 for other applications where oil-free air is re- 

 quired. 



The rotary- centrifugal compressor, shown in 

 figure 17-11, consists of a round, multi-bladed 

 rotor which revolves freely in an elliptical cas- 

 ing. The elliptical casing is partially filled with 

 high-purity water. The curved rotor blades 

 project radially from the hub. The blades, to- 

 gether with the side shrouds, form a series of 

 pockets or buckets around the periphery. The 

 rotor, which is keyed to the shaft of an electric 

 motor, revolves at a speed high enough to throw 

 the liquid out from the center by centrifugal 

 force, resulting in a solid ring of liquid revolv- 

 ing in the casing at the same speed as the rotor 

 but following the elliptical shape of the casing. 

 This action alternately forces the liquid to enter 

 and recede from the buckets in the rotor at high 

 velocity. 



To follow through a complete cycle of oper*- 

 ation, let us start at point A_. The chamber (1) is 

 full of liquid. The liquid, because of centrifugal 

 force, follows the casing, withdraws from the 

 rotor, and pulls air in through the inlet port. At 

 (2) the liquid has been thrown outward from the 

 chamber in the rotor and has been replaced with 

 atmospheric air. As the rotation continues, the 

 converging wall (3) of the casing forces the liquid 

 back into the rotor chamber, compressing the 

 trapped air and forcing it out through the 

 discharge port. The rotor chamber (4) is now full 



INLET 



DISCHARGE 



INLET. 

 PORT 



DISCHARGE 

 — PORT 



147.119 



Figure 17-11.— Rotary- centrifugal compressor. 

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