Hydraulic power pack pumps, hydraulic motors and associated plant are common noise problems for both occupational noise and as a source of environmental noise complaints. From the perspective of noise, they are usually badly designed as pump and valve vibration is radiated as high levels of noise.
Acoustic enclosures as noise control for hydraulic power packs and pumps cause maintenance and operational problems. There are better alternatives that don't cause increased temperatures (forced ventilation is usually required) and hidden oil leaks.
The low-cost, innovative engineering noise control measures described below can cut noise at source by 10dB - 20dB without the issues associated with acoustic enclosures.
Hydraulic pump and motor noise is dominated by the oil pressure pulsations created by the pumping action (as oil is incompressible). This generates very high forces causing vibration to be transmitted into the surrounding structures and pipework from which it is radiated as sound. The noise generated has a characteristic signature with a "toothcomb" of pumping frequency tones over a wide frequency range as shown here.
The key is an accurate diagnosis of the noise-generating mechanisms and vibration transmission paths as described below. It is then possible to determine the optimum retrofit engineering vibration isolation and damping noise control modifications.
The efficacy of this approach is demonstrated by the 9dB(A) noise reduction achieved on this baler hydraulic power pack without any form of enclosure and without any effect on maintenance or normal operation. In fact, the reduced levels of vibration also reduce the likelihood of pipe/joint fatigue and oil leaks.
The diagnostic process involves carrying out a narrow-band frequency analysis - this can even be done by using a free smartphone app - coupled with an accurate ranking of the sound power of each of the noise-radiating surfaces using a combination of noise and vibration measurements. This ranking is then used to prioritise the noise reduction treatments, starting with the dominant source and then working down the ranked list. This process eliminates any guesswork and ensures that the most cost-effective solution is implemented.
Hydraulic noise control
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Where it is difficult to use power pack noise for detailed diagnosis (the tonal source generates standing waves), we use vibration measurements to determine the ranked transmission paths. Typically, it is the pump and/or the valve block that are the dominant vibration sources. It is then possible to design simple retrofit vibration isolation measures based on the frequency analysis. This ranges from very simple compressible gaskets to more sophisticated isolation depending on the application. It is important to ensure that there are no vibration short circuits.
Where environmental noise nuisance is an issue (low levels of tonal noise in offices etc or off-site), then it is more common that the methods used to connect pipework to buildings or other structures are also evaluated.
Tonal hydraulic pump and motor vibration is transmitted into structural elements that radiate the sound. Where practical, vibration isolation is usually more effective than damping. However, high-efficiency damping applied to the radiating surfaces can also be a simpler and very effective way to cut vibration and hence noise levels, either replacing thin panels or retrofitting to the vibrating elements. https://sounddampedsteel.com/laminated-metal-how-does-it-work/.
In some cases, the installation of a carefully chosen inline hydraulic silencer can be used to reduce the pressure pulsations transmitted down high-pressure pipes to reduce the noise generated further downstream. The design of the silencer must take into account the line pressure and flow and the frequency range of the problem pulsations.
Whilst controlling vibration to reduce noise is the best approach, local acoustic barriers can provide additional attenuation. They can even be used instead of source control where noise radiation in only one direction is an issue.
Acoustic enclosures, however, should only be used as a last resort for the reasons detailed above. If they are installed, great care must be taken to ensure that there is adequate ventilation as noise enclosures are inherently very effective thermal lagging. We have encountered instances where the enclosure performance is very poor as the power pack pipework noise (pipework that is outside the enclosure) is a substantial noise contributor, highlighting a lack of proper diagnosis.
We recommend this simple procedure to evaluate the best noise control measures for any project involving hydraulic power packs, pumps and motors. Alternatively, you can delegate the whole process to us as a turnkey service.
We provide the initial steps (1, 2 and 3) as a free service for an accurate diagnosis and to provide the costed noise control options. This is followed by detailed recommendations for implementation by local contractors to minimise costs. Typically, no site visit is necessary, so the service is available anywhere in the world) via remote control of noise.