求翻译：1.与电动机相比,在同等体积下，液压装置能产生更大的动力，也就是说，在同等功率下，液压装置的体积小、重量轻、结构紧凑，即它具有大的功率密度或力密度，力密度在这里指工作压力。是什么意思？

1 compared with the motor, the same volume, the hydraulic unit can produce more power, that is, the same power, hydraulics, small size, light weight, compact, that it has a large power density or power density, power density here refers to the work pressure.