Which ratio would be incorrect when describing the standard three compressor types' compression ratios?

• A. 20:1
• B. 4:1
• C. 8:1
• D. 6:1

Answer: (D)

Compression ratio is how much the refrigerant’s pressure is increased from suction to discharge. The three common compressor types are suited to different pressure lifts, so each has a typical compression ratio range. Screw compressors are designed for moderate, steady pressure rises, commonly around 4:1. Reciprocating (piston) compressors can achieve higher pressure lifts, often about 8:1. Centrifugal compressors handle large volumes and, in multi-stage setups with intercooling, can reach high overall ratios, around 20:1. A ratio of 6:1 doesn’t fit these usual ranges for any of the three types, so it wouldn’t be described as a standard compression ratio for the three common compressor types. The other ratios align with the typical values for screw, reciprocating, and centrifugal units. Real-world ratios depend on suction and discharge pressures and system design.