Created on:2021-11-09 13:05

Working principle of QY20B truck crane hydraulic system

Working principle of QY20B truck crane hydraulic system

1. Introduction

One qyzob truck crane had the following faults during operation: at the beginning of slewing, the third gear pump of the triple gear pump suddenly broke its shaft four times, and the other two pumps worked well; Then, after replacing the new triple gear pump, continue to start the crane. It is found that the slewing mechanism fails and other mechanisms work normally. According to the hydraulic system schematic diagram of the crane, the hydraulic circuit of the third gear pump in the three gear pump on QY20B truck crane is analyzed to find out the causes of the fault and solve the problems of shaft breakage and rotation failure of the gear pump.

2. Working principle of QY20B truck crane hydraulic system

As shown in Figure F, the hydraulic system of QY20B truck crane is supplied with oil by a three gear pump, and the first pump 1 is supplied to telescopic hydraulic cylinder 17 and luffing hydraulic cylinder 18 or combined with the second pump 2 to supply winch motor 19; The second pump 2 supplies oil to the winch motor; The third pump 3 supplies the lower outrigger hydraulic cylinder or the upper slewing hydraulic motor, winch clutch hydraulic cylinder and winch brake hydraulic cylinder.

F2.jpg

The third pump supplies oil to the outrigger or rotary hydraulic motor 16 through the outrigger control valve 4. When the positioning control valve 5 is placed in the upper position and the distribution valve 7 and oil outlet valve 8 are in the middle position, the hydraulic oil discharged by the pump returns to the oil tank through the above valves in turn, and the third pump is in the low-pressure unloading state. When the distribution valve 7 in the outrigger control valve 4 is pulled, the pressure oil enters the outrigger horizontal hydraulic cylinder to extend or retract the four outriggers at the same time. When the distribution valve 7 is in the middle position and the oil outlet valve 8 is pulled, the pressure oil enters the four outrigger vertical hydraulic cylinders respectively through the rotary valve 9 to realize the vertical lifting action of the outrigger. After the outrigger is placed, place the positioning control valve 5 of the outrigger control valve 4 in the lower position. At this time, the oil discharged from the third unit pump supplies oil to the slewing hydraulic motor 16 through the first unit of pilot sequence valve 14 and multi-way valve 15, and supplies oil to the winch mechanism clutch and brake system through oil filter 13 and combination valve 12.

The hydraulic oil discharged from the third pump is depressurized through the oil filter 13 and the combination valve 12, filled with liquid 11 and supplied to the vertical lowering control valve 10. The oil pressure in the accumulator 11 is led to the upper chamber of the ejector rod of the pilot sequence valve 14. When the pressure in accumulator 11 is high and the sum of the inlet pressure of ejector rod and sequence valve 14 is greater than the set pressure of pilot sequence valve 14, pilot sequence valve 14 opens and the third combined pump supplies oil to swing hydraulic motor 16 through multi-way valve 15. When the pressure of accumulator 11 is lower than the set pressure of pilot sequence valve 14 and the hydraulic pressure at the inlet of pilot sequence valve 14 is lower than its set pressure, pilot sequence valve 14 is closed, and the oil circuit of the third combined pump and swing hydraulic motor is cut off to supply oil to accumulator 11 and its rear oil circuit.

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