A compressor in which a supersonic velocity is imparted to the fluid relative to the rotor blades, the stator blades, or both the rotor and the stator blades, producing oblique shock waves over the blades to obtain a high-pressure rise. But sometimes the supersonic compressor may produce shock waves that obtain a low pressure rise. In this case, the compressor fails to reach its maximum potential.
Single-stage compressors raise the fluid pressure from inlet to discharge on each working stroke of the piston in each cylinder. Two-stage compressors use one cylinder to compress the fluid to an intermediate pressure and another cylinder to raise it to final discharge pressure. When more than two stages are used, the compressor is called a multistage unit.
Vertical and horizontal compressors may be single-cylinder or multicylinder units. The angle type is multicylinder with one or more horizontal and vertical compressing elements. Single-frame (straight-line) units are horizontal or vertical, double-acting, with one or more cylinders in line with a single frame having one crank throw, connecting rod and crosshead.
In the lobed rotary compressor, fluid is trapped between two or more rotors held in fixed relationship to each other. Rotation of the impellers reduces the volume in which the fluid is trapped, producing a pressure rise. Fluid is discharged when the rotors pass the outlet port. Either two or three rotors are used.
In the sliding-vane rotary compressor, fluid is trapped between vanes as the rotor passes the inlet opening. Further rotation of the rotor reduces the volume of the space in which the fluid is trapped. Fluid pressure rises until the discharge port is reached, when discharge occurs.