US Patent 6964162 Hydraulic pressure generating apparatus

A hydraulic pressure generating apparatus includes a hydraulic oil feed line for feeding hydraulic oil with high pressure from an oil tank to a hydraulic pressure control system of a generator by an oil feeding pump unit, a hydraulic oil return line for returning drain oil from the hydraulic pressure control system to the oil tank, and a circulation line for circulating and purifying the hydraulic oil of the oil tank by a circulating pump unit. In such apparatus, the hydraulic oil is flame resistant hydraulic oil which is hardly deteriorated by direct heating, and the flame resistant hydraulic oil is heated by a heater disposed in the oil tank.