Analysis of the Causes of the failure of Concrete Pump trucks to pump

Analysis of the reasons for the failure of concrete pump trucks to pump:

A SY5255 37m pump truck encountered a fault when returning to the mixing plant for car washing after the pumping was completed. The speed increase was normal, but the pump could not be pumped in either forward or reverse direction. The normal acceleration indicates that the PLC can detect the speed signal of the transfer case. Continue to check the pump point control Q2.0 and Q2.1. The normal lighting indicates that the electrical control signal is normal. The hydraulic control system should be the focus of inspection.

Check whether the coil of the DT1/DT2 solenoid valve is short-circuited or open-circuited, or whether there is a fault in the circuit from the solenoid valve to the PLC.

(2) Check if the DT1 solenoid valve is stuck, which causes the relief pressure of the relief valve to fail to be established. If the valve core of the DT2 solenoid valve is stuck in the middle position, it will lead to the loss of control of the forward and reverse pumps.

(3) Whether there is any fault with the main pump.

Inspection findings:

(1) Observe the pressure gauges of the forward and reverse pumps. If the pressure is 0, there is no pressure in the system.

(2) The DT1 solenoid valve was found to be energized normally. Later, when the valve core was manually pushed, the fault persisted.

(3) If it is suspected that the valve core of the relief valve is stuck, remove the top cover to take out the valve core. The valve core can move up and down smoothly and normally. Remove the spring and replace it with five coins. Install the valve core cover plate. If the fault persists during the test run, it indicates that the relief valve is functioning properly.

(4) Further detection was carried out, and it was found that all functions of the boom and piston retraction were abnormal. The speed could be automatically adjusted. At the same time, it was discovered that all three pressure gauges showed zero. It indicates that the fault should be in the pressure output section of the main pump.

(5) If the power supply to the pumping solenoid valve is normal, it indicates that the driving and pumping position detection should be normal. However, upon re-testing, if I2.5 is lit up, the proximity switch for the transfer case position detection is lit up, and the driving and pumping actions of the vehicle follow the operation actions of the cab normally, it indicates that there is no fault in the driving and pumping control circuits. The engine accelerates normally, and there is no pressure in the system. The position detection also shows no faults. Therefore, it is determined that the fault is a problem with the internal fork of the transfer case.

(6) After disassembling the transfer case, it was found that the splines and gears of the third main shaft were damaged. After replacement, the fault was completely eliminated.