Hydraulic power pack pump noise reduction techniques
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.
What causes hydraulic power pack pump and motor noise?
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.
How to achieve hydraulic power pack noise reduction without acoustic enclosures
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.
Noise diagnosis
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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Engineering hydraulic power pack noise control measures
Vibration isolation
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.
Vibration damping
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/.
Hydraulic silencers
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.
Acoustic barriers or enclosures?
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.
Hydraulic power pack noise reduction made simple: the process
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.
- Noise analysis: use a free smartphone spectrum analysis app to check tonal content - or send a video clip to us email smartphone recordings to us for free analysis
- Diagnosis and ranking: rank the noise-radiating surface and vibration transmission paths and determine the frequency range over which attenuation is required
- Determine the best noise source control measures: select and implement the optimum noise reduction options for the dominant source(s) as described above
- Noise reduction check: check the tonal frequency content and the overall noise level
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.
The hydraulic power pack driving a baler was the cause of both occupational noise issues on-site and noise complaints off-site. Whilst the former was simply a case of the overall noise level at 87dB(A) requiring the use of hearing protection, the latter was a result of the highly tonal - and therefore annoying - nature of the noise. We designed engineering noise control modifications that not only cut the overall noise level to 76dB(A) at 1m (no PPE required), but also eliminated the tonal noise issue.
How was the hydraulic noise reduced?
The noise sources were ranked and modified as follows:-
- Vibration from the submerged hydraulic motor/pump unit into the oil tank: unit vibration isolated from the oil tank to reduce the high-frequency tonal noise
- Valve block vibration into oil tank: high-frequency vibration isolation
- Thin steel panels: damped
- Small local acoustic screen: to reduce noise traveling off-site
Care was taken to ensure that there were no vibration isolation short circuits.
These modifications cut the overall noise from the power pack by 9dB(A). In addition, care had been taken to address the off-site tonal noise problem. The major problem tones were reduced by up to 17dB (98%) as shown by this narrow band frequency analysis.
The engineering modifications were low-cost, easy to install using a local contractor and had no effect on normal operation, access or maintenance.
View detailed hydraulic power pack, pump and motor noise control guidance >
The 96 dB(A)Leq recorded from a 250 ton Rhodes billet hydraulic guillotine was cut by 17dB(A) – without using an acoustic enclosure. This was not only very low cost, but it also avoided the associated access, maintenance, and temperature issues.
Dominant hydraulic power pack noise reduced
Diagnosis showed that the overall noise from the guillotine was dominated by high levels of vibration transmitted from the hydraulic pump into the machine frame (and through rigid pipework to the remainder of the machine). In addition, there was also a significant transmission of impacts from the hydraulic valve bank.
The engineering solution was to mount the hydraulic motor-pump unit on a damped rigid frame that was then isolated from the machine body. The valve bank was also vibration-isolated from the machine frame using a tuned section of rubber-cork composite.
These modifications reduced the hydraulic power pack noise from 96 dB(A) down to 79 dB(A) at a fraction of the cost and without the operational and maintenance issues that would have been introduced by the previously proposed acoustic enclosure.
View detailed hydraulic power pack, pump and motor noise control guidance >
The manufacturer of hydraulic power packs for offshore use had to meet a very tight customer Buy Quiet noise purchasing specification. The unit had to include an acoustic enclosure within a very tight space for environmental reasons. In order to meet the requirements, we designed a combination of engineering control measures to reduce the power pack noise at source combined with an acoustic enclosure that included features to provide the required attenuation within significantly less space than a conventional soundproof box.
Hydraulic power pack noise sources and noise reduction features
The hydraulic power pack noise sources are listed below in rank order:-
- hydraulic pump and associated vibration
- oil cooler fan
- pump motor, including fan
The noise from each source was reduced at source as far as practical to ensure that the dimensions of the acoustic enclosure were within the space constraints without compromising cooling. The following were the design features:-
- hydraulic power pack pump noise: control at source using high-efficiency damping
- oil cooler fan noise: geometric features coupled with compact, bespoke silencing to provide high attenuation without compromising cooling
- acoustic enclosure panels: included high-performance damping and tuned acoustic absorbent.
The detailed design was developed in conjunction with SoundDampedSteel who supplied both the highly damped laminated steel used and the enclosure itself to our specifications.
This project was carried out entirely remotely (no site visit) by email and smartphone using streamed pictures from site.
View detailed hydraulic power pack, pump and motor noise control guidance >
