Noise; How is it created?
Noise is a by-product of inefficiency caused by the conversion of energy from one form to another. Nearly every component of a hydraulic system is likely to be associated with noise.
- Electric Motors – The predominant noise generator within the electric motor is the cooling fan. In many cases the electric motors’ cooling fan is louder than the pump.
- Pumps – Most hydraulic pumps are actually a series of pumps contained within one body. Piston pumps contain several pistons, vane and gear pumps each contain several pumping chambers. Each pumping chamber sweeps fluid from the reservoir and transports it to the pumps’ outlet port. Several pumping chambers combine to produce total pump output flow.
Energy is stored in the fluid as it changes state from low pressure to high. If this fluid is decompressed rapidly, energy is released and noise is one of the by-products. The more rapidly this fluid is decompressed the more likely that noise will be produced.Pump manufactures go to great lengths to provide each pumping chamber with gradual decompression, thus rendering the pump quiet, or more quiet than otherwise.When air is introduced to the pump inlet (cavitation) all bets are off. Lots of bad things can happen when air is introduced into a hydraulic system, excessive pump noise being only one.
- Pump/Motor Couplings – Pump to motor misalignment can dramatically add to the overall noise level of the hydraulic system. So can windage -just ask your dog.
The pump/motor combination is generally the highest noise generator with a hydraulic system, but other components can generate substantial noise as well.
- Pressure Control Valves – Rapid decompression of fluid within a pressure control valve can create objectionable noise.
- Flow Control Valves – Noise can be created within these valves as fluid rapidly changes directions. The orifice action can also produce a “whistling” effect.
- Directional Control Valves – The same characteristics associated with flow control valves can also become apparent in directional control valves.
Noise; Can it be eliminated from a hydraulic system?
No
Noise; How can it be minimized within a hydraulic system?
Special attention to the mechanical layout and design of the hydraulic system is crucial to minimizing noise such as:
- Stout reservoir design
- Placing the pump beneath the reservoir fluid level
- Reduce pump RPM
- Do not use pump suction strainers
- Do not under-size the pumps’ inlet line
- Use few if any elbows, couplings or unions in the pump inlet line
- Mount the pump directly to the electric motor
- Make all pump connections with hose rather than pipe or tube
- Utilize resilient mounts on the electric motor feet
- Keep fluid velocities throughout the system to acceptable limits (do not under-size piping)
- Support your plumbing, don’t just let it hang
- Apply shrouding with sound dampening material
- Pulsation dampeners in the pump outlet lines
- The use of accumulators can sometimes reduce overall noise
Noise; Some examples
Noise level is considered to have doubled for every 3 additional dBA, so every decibel you can take out counts.
Referring to the chart on page 6, you can see the dramatic effect of adding two noise generators (pump + motor, two pumps, etc.). In Example “B”, the pump alone produces 72 dBA; however, adding the noise from the electric motor increases the system noise level to about 77.4 dBA. This is almost 4 times as loud as the pump alone!
Sound enclosures – can eliminate several decibels depending on the application
Elbows – each elbow in a pump suction line can be responsible for up to 1 decibel in additional noise
Motor Shock Mounts – can eliminate 1 – 2 decibels
Pulsation Dampeners – small in-line accumulators that can eliminate up to 1 – 2 decibels depending on the application
Motor Fans – In our example # 2 on page 4 you can see that the electric motor has added 5.4 decibels to the overall noise level of the system. Almost all of this is from the motors’ fan. Fan motor noise can be eliminated or greatly reduced by:
- Using ODP motors which usually use only very small fans
- Using Integrated Motor Pump assemblies (IMP’s). There are no fans involved with the electric motor. The motor is actually cooled by the hydraulic fluid passing through the motor windings.
Conclusion
We must all be conscious of noise in the work environment. There are limited measures that can be taken to reduce noise and improve sound quality on existing systems. The best way to address this pollutant is during the system design, component selection and construction.
When in doubt, consult your local fluid power professional.