Extremely easy operation and maintenance: Adjustment and maintenance works are very easy as basically the conventional power unit is used. Significant reduction of power consumption: With rotational frequency control, more than 40% of power consumption at pressure holding is possible compared to conventional hydraulic units. Low Noise: Especially the noise level at the full-cutoff is reduced. Discharge volume can be set to a certain volume at 50/60 Hz: Regardless the power supply frequency, the rotation speed at the maximum discharge volume can be set by the inverter within the range from 1500 to 1800 r/min. Continuous operation is possible even at breakdown of the pressure sensor or the inverter: Operation at a certain rotation speed is possible even without receiving a signal from the pressure sensor due to breaking of wire or malfunction of the pressure sensor. Incase of malfunction of the inverter itself, the same operation mentioned above is possible by reconnecting of the primary power supply to the electric motor.