How is the compression ratio calculated for a compressor with a suction pressure of 30 psig and a discharge pressure of 125 psig?

To calculate the compression ratio for a compressor, you use the formula:

Compression Ratio = (Discharge Pressure + Atmospheric Pressure) / (Suction Pressure + Atmospheric Pressure)

First, it is important to convert the pressures from psig (pounds per square inch gauge) to psia (pounds per square inch absolute). This is done by adding atmospheric pressure, which is approximately 14.7 psi at sea level, to each of the gauge pressures.

For the given suction pressure of 30 psig:

• Suction Pressure in psia = 30 psig + 14.7 psia = 44.7 psia

For the given discharge pressure of 125 psig:

• Discharge Pressure in psia = 125 psig + 14.7 psia = 139.7 psia

Now substituting these values into the compression ratio formula, we get:

Compression Ratio = (139.7 psia) / (44.7 psia) ≈ 3.13

Therefore, the correct option is indeed 3.13, as it accurately reflects the relationship between the discharge and suction pressures, accounting for atmospheric pressure. This value indicates how much the compressor is increasing the pressure