Rotary mechanism control is a decisive criterion for the evaluation of mobile crane. To ensure that the load is independent of other actuating components is the most basic requirement, so the independent hydraulic circuit is preferred.The rotary circuit of QUY50 crawler crane produced by xuzhou heavy machinery is composed of fixed pump, 6 way directional valve and fixed motor and is controlled by hydraulic pilot proportional.After several years of market test, its performance is more stable, the product is more mature.Its principle is shown in the figure below:

When working, first open the rotary solenoid valve 13, and the pilot pump provides a stable pressure oil source to ensure that the rotary brake 8 is opened.Then, by pushing or pulling the pilot handle 3, the pilot pressure oil smoothly opens the spool of the hydraulic control valve 5, and the pressure oil flow of the main pump passes through the hydraulic control valve.Drive the rotation of rotary motor 7 to complete the rotation process.When not working, the pilot handle 3 in the middle, hydraulic control valve 5 spool by spring recovery in the middle, the oil in the main oil circuit will be low pressure from the P port through the main valve flow back to the tank.The system has the following characteristics:

First, hydraulic control valve 5 spool full cover and minimal spool tolerance can reduce internal leakage, and the precise fine tuning control range can be sensitive to control the executive components, the sensitive control range depends on the driving speed and load pressure and hydraulic pilot proportional control.

Two, hydraulic control valve with primary relief valve and secondary relief valve.Because a very important function of the relief valve is to protect the safety of the system.Primary relief valve 4**** the maximum pressure of the hydraulic system to ensure system safety.Under the normal operation of the system, the relief valve is closed, and the working pressure of the system is determined by the external load.When the system pressure reaches the set pressure of the valve, the relief valve opens to play the role of unloading.At the moment when the rotary mechanism starts or brakes, the pressure will rise rapidly or even reach the peak value, which leads to the phenomenon of unstable system work. The secondary relief valve 10,11 weakens the pressure peak value and ensures the stability of the system.