The bulb injection machine is used for molding special equipment such as plastic products and nylon products. The working process of the injection molding machine has the functions of lifting, heating, clamping, injection, pressure keeping and mold opening. In a working cycle, the actual pressure and actual flow of the injection molding machine are varied, from large to small, sometimes almost zero. When the actual flow rate is small, the oil supply of the oil pump is far greater than the actual consumption of the load, and the supply exceeds demand. The surplus hydraulic oil under high pressure overflows through the overflow valve. The hydraulic oil under high pressure discharges a large amount of heat energy through the overflow valve, and this part of the dissipated energy is actually a part of the oil pump motor absorbing electric energy from the grid.