Abstract: Noise is a frequent fault of hydraulic system.For a long time,the designers reduced the noise often by eliminating vibration,adding throttles and exhausts,strengthening maintenance and inspecting,etc.The hydraulic power unit is a very important part of industrial hydraulic system,and also an important noise source.In this paper,based on the structure analysis of the hydraulic power unit,the causation of noises produced by the hydraulic power unit is discussed,and the measures to reduce the noises are introd...