An accumulator is a storage device in a hydraulic pump system. When the system needs energy, it converts heat within the system into compressive energy or potential energy, storing it. This compressive or potential energy is then converted into hydraulic or pneumatic energy, which is released when the system needs energy again, replenishing the system. In the event of a sudden increase in system pressure, it can absorb this energy, ensuring normal overall system pressure. Accumulators have two main uses:

　　① When the pressure changes, the required total flow rate is lower than the total flow rate of the hydraulic oil pump. The unnecessary total flow rate of the hydraulic oil pump is stored in the accumulator. When the total flow rate required by the load is higher than the flow rate of the hydraulic oil pump, liquid is released from the accumulator to make up for the insufficient flow rate of the hydraulic oil pump.

　　When the system is shut down but still needs to maintain a certain pressure, the hydraulic pump can be stopped, and the battery system will compensate to maintain the system pressure. The battery can also absorb pressure pulses from the hydraulic pump or absorb hydraulic shock pressures caused by the system. Pressure in energy storage devices can be generated by compressed air, a counterweight, or a torsion spring. Energy storage devices are correspondingly divided into vapor energy storage, liquid energy storage, and torsion spring energy storage. In vapor batteries, the gas directly contacts the liquid, called a gas-filled battery. It has a simple structure and large volume, but the liquid is prone to mixing with gas; it is commonly found in hydraulic presses.

　　Liquid-gas separation type, also known as liquid-gas separation type, usually uses gas or diaphragm for protection. The gas volume changes greatly, while the diaphragm volume changes little. It is commonly used in applications with fluctuating absorption pressure. The counterweight type has a larger volume and is mostly used in energy storage hot continuous rolling and other systems.