Which of the following is NOT a typical compression ratio for any of the three specified compressor types?

• A. 20:1
• B. 4:1
• C. 8:1
• D. 6:1

Answer: (D)

Compression ratio is how much the pressure of the refrigerant is increased from suction to discharge. Each compressor type has a practical operating window where it performs best, and the three common ammonia compressor families are typically designed around certain overall ratios rather than any single mid-range value. Some setups achieve about four-to-one, others are designed to reach closer to eight-to-one with multiple stages, and only specific high-stage configurations push toward the very high end, like twenty-to-one. A six-to-one ratio doesn’t align with the standard envelopes for any of these three types, so it isn’t considered a typical operating ratio. In practice, engineers select the stage count and design to hit the ratio that matches the chosen configuration and efficiency goals.