액체에 의해 구동되는 용적형기관(액체 및 압축성유체용 용적형기관 f01; 액체용용적형기계; 유체압 액추에이터(actuator) f15b; 유체전동장치 f16h) positive-displacement engines driven by liquids (positive-displacement engines for liquids and elastic fluids f01; positive-displacement machines for liquids f04; fluid-pressure actuators f15b; fluid gearing f16h) 