Figure 1. So-called whispering power units do not rely on enclosures to muffle sound, they incorporate smarter design to keep noise as much as 20 dB(A) lower than standard power units.Noise in hydraulic systems can be created by many components. Pressure drop and turbulent flow create the energy, which is then transmitted — and often amplified — by other components or structural members. Many times, conflicting constraints amplify the situation. For example, cost constraints may drive smaller line sizes or structural members, which then have less mass to absorb the energy — and have a lower resonant frequency. Some other issues to consider:
● Minimizing pressure drops and line speeds are good hydraulic design guidelines anyway, but they must be emphasized when noise is an issue.
● Tank design and supporting structure must be considered carefully to minimize vibration transmission.
● Components known to have inherent noise or vibration are best isolated (or de-coupled) from supporting structure or rigidly mounted items.
● High efficiency and balanced electric motors, pulsation dampers, creative design of the tank and supporting structure, and axial-piston pumps are all features that can be incorporated.
● Pulsation dampers can help reduce pulsations inherent in the system. If the machine duty cycle is regular and specific, an accumulator drive circuit may be appropriate, which can greatly reduce the size of the pump and motor required. Because the motor and pump are usually the source of most of the HPU noise, a smaller motor-pump would operate more quietly. Of course, sizing the plumbing must be done carefully to minimize pressure drop and line noise.
Most noise-reduction practices involve inherent costs, so before specifying a maximum noise level, you may want to consider what is really necessary before being shocked at the cost of what was specified.
Accumulator charging circuits