Which is the correct ratio for a screw compressor among the following options?

Which is the correct ratio for a screw compressor among the following options?

• A. 20:1
• B. 4:1
• C. 6:1
• D. 8:1

Answer: (A)

The main idea here is the pressure ratio across a screw compressor—the discharge pressure (absolute) divided by the suction pressure (absolute). Screw compressors are designed to deliver a relatively large pressure rise in one stage to push ammonia up to condenser pressure while keeping the unit compact. In typical ammonia systems, the combination of low evaporating temperatures and the condenser pressures needed to reject heat results in a high pressure ratio, often around twenty to one. That makes a 20:1 ratio the best representation among common options. The smaller ratios reflect lower head pressures or different compressor configurations and don’t match the usual design targets for ammonia screw equipment.

The main idea here is the pressure ratio across a screw compressor—the discharge pressure (absolute) divided by the suction pressure (absolute). Screw compressors are designed to deliver a relatively large pressure rise in one stage to push ammonia up to condenser pressure while keeping the unit compact. In typical ammonia systems, the combination of low evaporating temperatures and the condenser pressures needed to reject heat results in a high pressure ratio, often around twenty to one. That makes a 20:1 ratio the best representation among common options. The smaller ratios reflect lower head pressures or different compressor configurations and don’t match the usual design targets for ammonia screw equipment.