ZLYZInner and outer double brake system of type-I drum
（1） Working principle and shape structure:
Working principle: spring brake and hydraulic release are used for internal and external brakes. When the power is lost, the solenoid valve on the main oil circuit is in a normally open state. Due to the spring extension, the hydraulic oil in the oil cylinder returns to the oil tank along the oil path, causing the friction between the internal and external brake friction belt and the drum to produce braking torque. When the machine is working, the solenoid valve on the main oil circuit is closed, and the oil pump supplies oil to the oil cylinder, causing the piston rod of the internal brake cylinder to contract the compression spring and release the internal brake of the drum; at the same time, the piston rod of the external brake cylinder extends the compression spring to release the external brake of the drum, and the machine starts to work normally. Its outline structure is as follows:

2、 The characteristics of zlyz type drum internal and external braking system are as follows:
Compared with the ordinary disc brake system, its remarkable features are as follows:
  (1) The inner and outer double brake system of drum has compact structure and small volume, while the disc brake system has complex structure and large volume;      
  (2) The manufacturing cost of the inner and outer double brake system of the same specification is only 1 / 3 of that of the disc brake system;
  (3) It has high safety coefficient, and the braking safety of the double braking system inside and outside the drum. If one of the internal and external braking fails to work normally, the overall braking function will not be affected, and the braking is stable. However, if one side of the disc brake can not be used normally, the force will shift, resulting in the brake can not work normally, and the braking safety and stability are not high;
  (4) The braking torque of the inner and outer double braking system of the drum is large, and the braking torque of the inner and outer double braking system of the same specification is 4-5 times of that of the disc brake system;
  (5) The internal and external double braking system of the drum has the function of automatic over speed braking. If the transmission parts between the motor and the drum of the hoist are damaged or the high-speed braking fails, the hoisting weight of the hoist will suffer from over speed sliding. When the sliding speed reaches a certain value, the overspeed device installed in the double braking system inside and outside the drum will send out an alarm signal and make it automatically brake the drum to avoid The occurrence of dangerous accidents.
  (6) Through theoretical analysis and test data, the braking performance data of internal and external double braking system and disc brake system of the same specification are compared as follows: