Vibration Signatures of Reciprocating Compressors
Zhuang
Li,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: July 2007
Abstract
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.
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Introduction
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.
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