Abstract: In an injection molding machine of the type comprising an injection cylinder, a feedback circuit for feeding back the oil in the rear chamber of the injection cylinder into the front chamber thereof and a booster cylinder, a pressure oil accumulator is connected to the booster cylinder through a valve for supplying pressurized oil for actuating the booster cylinder. A check valve is connected in parallel with the valve. When water hammer occurs at the end of the injection stroke the check valve opens to absorb the energy of water hammer by the accumulator.

Abstract: In a die cast machine of the type wherein the piston of an injection cylinder is advanced by pressure gas admitted into the rear chamber of the cylinder while discharging pressurized liquid in the fore chamber, and the piston is retracted by pressurized liquid admitted into the fore chamber while forcing the gas in the rear chamber back into a gas accumulator, a control valve device is provided in the path of the pressurized liquid discharged from the fore chamber, and the control valve device is controlled so as to vary the flow quantity of the discharged pressurized liquid in accordance with the position of the piston during its forward movement. There are also provided two gas accumulators which are connected to the rear chamber of the cylinder through a valve device which is controlled so as to adjust the rate of increase of the pressure applied to the molten metal at the final stage of the injection casting operation.