A Niigata 11FB concrete pump in use appears to be weak in pumping, when the pressure on the pressure gauge slowly rises to 1/3 of the maximum pressure and then slowly drops to zero. The pump truck is provided with an electrical stroke switch (commonly known as a reed switch) at the end of the main hydraulic cylinder for pumping concrete. The commutation signal of the main hydraulic cylinder is controlled by a travel switch, and the electrical signal is transmitted to the main hydraulic cylinder through the electrical control system Commutation solenoid valve commutation; main hydraulic cylinder hydraulic pressure by the main safety valve control. The analysis of the causes of the failure may be due to: the main hydraulic pump failure; main safety valve malfunction, leakage; to the solenoid valve leakage; electrical stroke switch position improper; conduction circuit failure. The inspection found that the end of the main cylinder into the reed pipe pulled out too much to make the piston stroke shorter, the piston did not run to the front of the return operation, that is, unloading commutation, resulting in oil pressure can not be increased to a maximum value. After adjustment, the fault is removed. The adjustment steps are: ①open the fill valve, close the main hydraulic cylinder make up the oil, and then tightly close the needle valve; ② make the piston run several trips, then the engine speed of 1 000 r / min Left and right; ③ thinly coated with a layer of grease at the exit of the concrete cylinder; ④ each piston to do a maximum pressure test, the piston moved to the terminal, and the stop position of the piston coated with grease; ⑤ with 2 200 r / min engine speed suction, adjust the reed tube until the piston can be retracted in the end position about 50 mm (conversion action) prevail. Another Chutian brand HBT60 concrete pump in the normal work of a sudden gate action, pumping all disappear, the pressure gauge shows 0. The pump ram cylinder, concrete delivery cylinder all by the same main pump oil, hydraulic pressure by the main safety valve control, the main safety valve by the unloading solenoid valve control, unloading solenoid valve is a two-way four-way solenoid valve When the need to unload, the right power, solenoid valve in the right position, unloading through the overflow port. After analysis, the cause of the failure: ①main hydraulic pump failure; ② main safety valve, unloading solenoid valve poor work, leakage. Namely: First, the main safety valve spool with small particles on the cone debris, or cone valve back in the overflow process card issue, resulting in oil overflow, can not afford to build pressure, this failure occurred in the new purchase Equipment used in the run-in phase; second unloading solenoid valve in the course of the return card, or can not return to the left position, then just gently push the installation of the solenoid valve at both ends of the indicator bar, open or close the solenoid valve Switch, you can check whether the solenoid valve is working properly. If the circuit fails, the solenoid valve can not move, but at this time eager to pump, you can tighten the lock nut so that the working position of the solenoid valve left position, and then overhaul after the completion of work. If you need to stop pumping, loosen the lock nut so that it can work in the right position of the solenoid valve.