Basics of Reciprocating Compressors - Thermodynamics

Hello everyone! We’re back with Article 12, It will be the last article in 2024. Best wishes to everyone in 2025 and I hope, it will be a more successful year

We’ll continue exploring the basics of reciprocating compressors, this time diving deeper into the thermodynamics of reciprocating compressors.

Understanding Compressor Thermodynamics

A reciprocating compressor's thermodynamics is crucial for basic troubleshooting and evaluating compressor performance.

One of the most well-known tools for understanding this is the PV diagram (Pressure-Volume diagram). This diagram illustrates the dynamic relationship between volume and pressure as it changes with respect to the crankshaft’s angle of rotation.

Key Phases in the PV Diagram

In a typical PV card, you’ll observe four key phases:

1. Suction: Where the fresh gas enters the cylinder.

2. Compression: Where the piston reduces the volume, increasing pressure.

3. Discharge: The high-pressure gas is released.

4. Expansion: The piston moves back, increasing the volume and reducing pressure.

What Can You Learn from the PV Card?

The area under the curve on the PV card represents the power consumption of the compressor. By analyzing the PV card, you can gain valuable insights into the compressor’s operation.

Furthermore, by comparing the actual PV card with the theoretical PV card, you can detect potential deviations. These deviations can help diagnose issues such as:

? Internal gas leakages

? Valve malfunctions

? Worn-out piston rings or pressure packing issues

you can also obtain from the diagram, the piston displacement, stroke, volumetric efficiency...etc.

The Importance of PV Card Analysis

Reading and analyzing PV cards requires experience and practice, as it’s a fundamental tool in diagnosing compressor performance issues. Over time, you’ll gain the necessary skills to pinpoint inefficiencies and identify the exact areas of concern within the compressor.

The next Article will be about cylinder valve types and their pros and cons, stay tuned for the first article in 2025.