GCAP Industrial Ammonia Refrigeration Practice Test 2026 – Complete Exam Prep

When calculating a compression ratio, the correct pressure scale to use is PSIA, which stands for pounds per square inch absolute. This is because the compression ratio is defined as the ratio of the absolute pressure of the gas at the discharge of a compressor to the absolute pressure of the gas at the inlet. Using absolute pressure values ensures that you account for the complete range of pressures, including atmospheric pressure, which is critical in achieving accurate calculations.

PSIG (pounds per square inch gauge) measures pressure relative to atmospheric pressure and can lead to inaccuracies when calculating the compression ratio if atmospheric pressure is not considered. The BAR and ATM scales, while valid pressure units, may not provide the accuracy needed when interpreting specific industrial scenarios and may involve conversions that complicate the calculation. Therefore, sticking with PSIA simplifies the process and ensures precision when determining the compression ratio.