Zhuang Li & Suri Ganeriwala
Vibration Signatures of Reciprocating Compressors
SpectraQuest Inc., 8227 Hermitage Road, Richmond, VA 23228
Published: July, 01 2007
This tech notes studies the vibration signatures of a reciprocating piston compressor. A brief introduction of the operation principle and noise and vibration sources is presented. Experiments were carried out on a Spectra Quest's machinery fault simulator MFS Magnum with a single-piston compressor driven by the belt drive. The compression cycle and the related behaviors of different parts, including piston, inlet and discharge valves, are analyzed in detail from the acceleration data. Both the FFT-based spectral analysis and joint time-frequency analysis were conducted to study the frequency contents.
Compressors are widely used throughout the world in industry, automobiles, household appliances, and medical devices, from refrigerators to air-conditioners, from oil pipeline to dentists' drills. The vibration properties are one of the major concerns in many compressor applications. A low-noise refrigerator is apparently desired at every home. Various compressor designs are used in different applications. There are two basic types of compressors: positive displacement compressors and dynamic compressors. In each category, compressors can be further classified into subcategories. The reader is referred to Ref 1 for more information of different types of compressors and a comparison of performance. This tech note concentrates on the reciprocating compressor because it is the most commonly used type. It is estimated that there are more than 400 million compressors in the United States.
Reciprocating compressors are the oldest type designed for mass production, and are still the most versatile compressor design even today. They are normally used for small volumetric flow rate requirements. Figure 1 illustrates a schematic of the structure of a single-piston reciprocating compressor. A crank translates rotation into a reciprocating motion of the piston through a connection rod. Air or other type of gas is taken into the compressor cylinder through an inlet valve, and compressed air is expelled through a discharge valve. The operation of a reciprocating compressor is similar to that of an internal combustion engine. As the piston moves upwards to compress the working gas during the compression stroke, the inlet valve closes and the discharge valve opens when the cylinder pressure exceeds the discharge pressure. After the piston has reached the top dead center, it begins the suction stroke. The discharge valve closes and the inlet valve opens when the cylinder pressure falls below the inlet pressure. The main noise and vibration source of a reciprocating compressor is the time-varying gas pressure pulsations created between the inlet and discharge valves
Figure 1. MFS Magnum.
Fig 2: Time waveform of a typical compressor acceleration signal.