At present, the hydraulic clamping system is widely used in the machine tool industry. It is recognized by users for its large clamping force, convenient operation, and easy automation in cooperation with electrical appliances. However, in order to maintain the constant pressure of the system, the general tightening system makes the pump and motor run for a long time, which not only wastes valuable energy, increases the system heat, but also greatly reduces the service life of the hydraulic components. As a hydraulic accessory, the accumulator is more and more widely used in the hydraulic system of machine tools with the improvement of manufacturing technology. Therefore, in the hydraulic design of machine tools, the accumulator is used in the hydraulic clamping system and has received good results.

 （1） The working process of the accumulator used in the hydraulic clamping system

  As shown in Figure 6-1, when clamping operation is required, the section and 1 start, the hydraulic pump 2 starts to work, and part of the pressure oil enters the clamping cylinder 10, and the other part enters the accumulator 8 for storage. As the pressure rises, when the upper limit of the system pressure is reached, the pressure relay 6 sends a signal to stop the motor and hydraulic pump through the electrical control. At this time, the system pressure is maintained by the accumulator. With the leakage of the system, when the pressure drops to the lower limit of the pressure relay, the pressure relay sends a signal to start the motor and pump to supplement the oil pressure. The time from the stop of the hydraulic pump to the restart shall be determined according to the number of clamping cylinders in the system and the leakage of the system. According to experience, if the leakage control of the system is good, the interval time can reach 2~3 hours. This greatly reduces the running time of the motor and pump, reduces the heating of the system, and increases the service life of each element.

 （2） Type and parameter selection of accumulator

  Accumulators can be divided into gravity loaded, spring loaded and gas loaded. The gravity accumulator uses the potential energy of the hammer to store energy. The pressure generated by this accumulator depends on the weight of the hammer and the size of the plunger area. Spring loaded accumulator uses spring compression energy to store energy. The generation of the accumulator depends on the stiffness and compression of the spring. The working principle of the gas-loaded accumulator is based on Boyle's law.

  When in use, first charge the accumulator with air or nitrogen of predetermined pressure, and then under the pressure of the hydraulic pump, make the oil enter the accumulator through the oil hole to compress the air bag. The pressure of the air chamber and the oil chamber are always equal, so that the air bag is in a floating balance state. When the system needs oil, the oil is discharged under the action of gas pressure. When the system discharges excess high-pressure liquid, it is also stored in the accumulator by compressing the gas in it.

  The total volume of the accumulator is the inflation volume. It is very important to select the total volume of the accumulator correctly. The capacity is too small to meet the working requirements of the system. If the capacity is too large, it will increase the weight and size of the system.

 （3） Benefits of adding accumulator to hydraulic clamping system

  The addition of accumulator will bring the following benefits to the system;

 ①It can partially absorb the pulsation of the hydraulic pump and reduce the noise;

 ②Reduce the hydraulic impact caused by the end of the oil cylinder or the direction valve reversing;

 ③It can compensate the hydraulic pressure change caused by oil temperature change;

 ④When the pump or motor fails, the clamping work can still be completed for a long time.