Pump noise/vibration

Giilich, J. F. 2010. Centrifugal Pumps, 2nd ed. BerUn/New York Springer. This handbook starts with an introduction to flnid mechanics, then moves immediately into pump types, characteristics, applications, operation, and performance. Also addressed are pump noise, vibration, and wear. 

During this period, additional data is collected, including data associated with motor amperage draw, pump curve performance, interface control, and operational baseline parameters, such as noise, vibration, and performance specifications are initiated. 

Hydrostatic transmissions are available where the pump and motor are combined in a single rigid unit, usually referred to as close-coupled transmissions. This produces a very compact drive that can be encased in a sealed housing to protect it from its environment. By eliminating external plumbing, close coupling reduces noise, vibration, flow losses, and leakage. 

Some noise components will appear at very specific frequencies. A pump will vibrate a dewar a few times every second, and an AC power line near a critical amplifier will introduce noise at the line rate - 60 cycles per second (see Figure 1.8). The more fundamental noise sources, however, will add some noise more or less uniformly at all frequencies. This is referred to as white noise, by analogy to the fact that white light contains all wavelengths (frequencies) of light. Even if the noise is not quite white. 

Uses. In architectural and industrial appHcations vibrational isolators are used to reduce transmission of vibration into building stmctures from rotating or reciprocating machinery, such as ventilating fans, pumps, chillers, industrial machinery, and the piping and ductwork coimected to this equipment (6). Vibration isolators also can be used to isolate vibration-sensitive equipment or noise-sensitive areas from sources of vibration. Examples are special pneumatic isolators to protect electron microscopes, and isolators used to support floating concrete floors in recording studios. 

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

Suction Limitations of a Pump Whenever the pressure in a liquid drops below the vapor pressure corresponding to its temperature, the liquid will vaporize. When this happens within an operating pump, the vapor bubbles will be carried along to a point of higher pressure, where they suddenly collapse. This phenomenon is known as cavitation. Cavitation in a pump should be avoided, as it is accompanied by metal removal, vibration, reduced flow, loss in efficiency, and noise. When the absolute suction pressure is low, cavitation may occur in the pump inlet and damage result in the pump suction and on the impeller vanes near the inlet edges. To avoid this phenomenon, it is necessary to maintain a required net positive suction head (NPSH)r, which is the equivalent total head of liquid at the pump centerline less the vapor pressure p. Each pump manufacturer publishes curves relating (NPSH)r to capacity and speed for each pump. 

Textile motors Crane motors Determining the size of motor Sugar centrifuge motors Motors for deep-well pumps Motors for agricultural application Surface-cooled motors Torque motors or actuator motors Vibration and noise level Service factors Motors for hazardous locations Specification of motors for Zone 0 locations Specification of motors for Zone I locations Motors for Zone 2 locations Motors for mines, collieries and quarries Intrinsically safe circuits, type Ex. f Testing and certifying authorities Additional requirements for ciritical installations Motors for thermal power station auxiliaries Selection of a special-purpose motor... 

The effects of cavitation are noise and vibration. If the pump operates under cavitating conditions for enough time, the following can occur ... 

Normally there is some connection between the airflow rate and noise and vibration generation. This could modify the building construction either to prevent spreading or to diminish the levels of noise and vibrations from the air-handling units. This naturally includes all parts of these units, i.e., fans, pumps, and valves (see Chapters 5 and 9). The demands on noise insulation also include the noise and vibrations from the process equipment, which often has a higher level of noise and vibration than the ventilation system. 

In another laboratory, a vacuum pump was installed on a shelf buUt into a two-foot knee-hole well above the floor level. It was out of the way, off the floor, and easy to service. Noise was substantially reduced by attaching rubber stoppers to the pump s base plate as vibration absorbers. Connection to equipment was through a hole in the work top. 

The fourth-order coherent Raman spectrum of a liquid surface was observed by Fujiyoshi et al. [28]. The same authors later reported a spectrum with an improved signal-to-noise ratio and different angle of incidence [27]. A water solution of oxazine 170 dye was placed in air and irradiated with light pulses. The SH generation at the oxazine solution was extensively studied by Steinhurst and Owrutsky [24]. The pump and probe wavelength was tuned at 630 nm to be resonant with the one-photon electronic transition of the dye. The probability of the Raman transition to generate the vibrational coherence is enhanced by the resonance. The efficiency of SH generation is also enhanced. 

In the above discussion it is assumed that the available NPSH in the system is adequate to support the flow rate of liquid into the suction side of the pump. If the available NPSH is less than that required by the pump, cavitation occurs and the normal curves do not apply. In cavitation, some of the liquid vaporizes as it flows into the pump. As the vapour bubbles are carried into higher pressure regions of the pump they collapse, resulting in noise and vibration. High speed pumps are more prone to cavitation than low speed pumps. 

When a pump and a Stokes laser beam coincide on the sample and their difference frequency matches a particular molecular vibrational frequency, then SRS appears in the form of a gain of the Stokes pulse intensity and a loss of the pump pulse intensity, as first observed by Woodbury and Ng in 1962 [170] and by Jones and Stoicheff in 1964 [171], respectively (see Fig. 6.1). SRS has long been recognized as a highly sensitive spectroscopic tool for chemical analyses in the condensed and gas phases [172, 173, 29, 174]. For example, a shot-noise limited SRS spectrum of a single molecular monolayer was demonstrated by Heritage and Allara in 1980 [175]. In this section, we discuss the fundamental properties and applications of SRS microscopy, as was first successfully demonstrated by Nandakumar et al. [20] and subsequently reported by several research teams [21, 12, 13, 22]. 

A monitor to detect bearing wear is available on some seal-less pumps but they generally don t offer complete monitoring of all internal bearings for axial and radial wear. Seal-less pumps typically run so smoothly and quietly that it is usually not possible to determine by vibration or noise if a bearing is badly worn. 

Compute the required speed reduction of the pump. When the liquid viscosity exceeds 600 SSU, many pump manufacturers recommend that the speed of a rotary pump be reduced to permit operation without excessive noise or vibration. The speed reduction ususally recommended is shown in Table 6.28. 

Vibrations, sound, and noise are other examples of common industrial hazards. The most common injury because of vibration is sound-induced hearing loss. The vibrations of machines, high-speed pumps, generators, boilers, and conveyers produce unwanted sound noise. The adverse effects produced by these sounds are as follows ... 

Everything about these two systems seemed to be identical — except that one pump performed perfectly, whereas the second operated with great noise and vibration. The troublesome pumping system was dismantled several times, but nothing wrong could be found. 

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