If a reciprocating compressor has a suction pressure of 65 psig and a discharge pressure of 120 psig, what is the compression ratio?

The compression ratio of a reciprocating compressor is determined by the ratio of the absolute discharge pressure to the absolute suction pressure. To calculate the compression ratio, first, it's important to convert the pressure readings from pounds per square inch gauge (psig) to absolute pressures. This is done by adding the atmospheric pressure, which is approximately 14.7 psi at sea level.

For the given suction pressure of 65 psig, the absolute suction pressure can be calculated as:

65 psig + 14.7 psi = 79.7 psia

For the discharge pressure of 120 psig, the absolute discharge pressure is:

120 psig + 14.7 psi = 134.7 psia

Now, the compression ratio is calculated by dividing the absolute discharge pressure by the absolute suction pressure:

Compression Ratio = Absolute Discharge Pressure / Absolute Suction Pressure

Compression Ratio = 134.7 psia / 79.7 psia

Performing this calculation results in approximately:

Compression Ratio ≈ 1.69

This value matches the choice provided as C, confirming it as the correct answer. Understanding how to convert gauge pressure to absolute pressure and the method for calculating the compression ratio is crucial for interpreting the operational capabilities