When the stick cylinder of the long arm excavator is slowly and powerless during operation, we should check as follows.
1. Check whether the seal fails. First loosen the oil pipe in the low-pressure chamber, drain the hydraulic oil in the chamber, and then start the engine to inject pressure oil into the high-pressure chamber. No hydraulic oil flows out of the oil pipe in the low-pressure chamber, indicating that the piston seal of the stick cylinder is well sealed. If the seal fails, the hydraulic oil in the low-pressure chamber and the high-pressure chamber will be mutually channeled due to internal leakage.
2. Check whether the safety oil suction valve is normal. The safety oil suction valve is a two-way protection valve, which is installed on the actuator such as the hydraulic cylinder and the hydraulic motor. When a certain cavity of the hydraulic cylinder or the motor produces instantaneous high pressure, the high-pressure oil in the high-pressure cavity will open the relief valve in the safety oil suction valve to overflow. At the same time, the one-way valve of the safety oil suction valve in the negative pressure cavity will open to supplement the negative pressure by oil suction from the oil tank To protect the oil circuit.
Since two safety oil suction valves are installed on the working circuit of the stick cylinder, if one of the safety oil suction valves fails and becomes two-way through, or when the overflow pressure of the overflow valve is very low, the oil pressure in the oil chamber at this side cannot be established, and the pressure oil is directly discharged into the oil tank through the one-way valve or overflow valve, which makes the stick cylinder slow and weak or even unable to work. If the safety oil suction valve has this fault, the stick cylinder will automatically slow down after the operating handle is in the neutral position to stop, otherwise, the safety oil suction valve fault can be eliminated.
3. Check PPC valve and main control valve. PPC valve, also known as pilot control valve, is a proportional pressure control valve. It can output corresponding control pressure and flow according to the size of the stroke of the operating handle, so that there is corresponding movement of the main control valve core, so as to control the speed of the actuator. Each valve element in the main control valve controls the on-off of an oil circuit. If one of the valve elements is worn, stuck or even blocked, the oil pressure and flow of the corresponding actuator will be reduced, causing the actuator to act slowly or even without action.
Change the control oil pipe of stick cylinder circuit to PPC valve which works normally and test the machine, then the fault disappears.