Six common faults in the hydraulic circuit of ZL50 loader (1)

This article uses actual cases to talk about common faults in the hydraulic circuit of the ZL50 loader working device. We first look at the fault symptoms and then discuss the solutions.

Fault phenomenon 1: Neither the bucket nor the boom moves

Reason analysis:
1) Hydraulic pump failure can be determined by measuring the outlet pressure of the pump. Possible reasons include the pump shaft being twisted or damaged, the rotation not working properly or stuck, the bearings being rusted or stuck, serious leakage, the floating side plate being severely strained or roughened, etc.
2) The filter is clogged and accompanied by noise.
3) The suction pipe is broken or the pipe joint with the pump is loose.
4) There is too little oil in the fuel tank.
5) The fuel tank vent is blocked.
6) The main relief valve in the multi-way valve is damaged and fails.
Troubleshooting method: Check the hydraulic pump, find out the cause, and eliminate the hydraulic pump failure; clean or replace the filter screen: check the pipelines, joints, tank vents and main relief valve to eliminate the fault.

Fault phenomenon 2: Boom lifting is weak

Reason analysis:
The direct reason for the weak lifting of the boom is insufficient pressure in the rodless chamber of the boom hydraulic cylinder. The main reasons are: 1) There is serious leakage in the hydraulic pump or the filter is clogged, resulting in insufficient oil delivery by the hydraulic pump. 2) Serious internal and external leakage occurs in the hydraulic system. The causes of internal leakage include: the main safety valve pressure of the multi-way reversing valve is adjusted too low, or the main valve core is stuck in the open position by dirt (the spring of the main valve core of the pilot valve is very soft and is easily blocked by dirt. stuck); the boom reversing valve in the multi-way valve is stuck in the drain position, the gap between the valve core and the valve body hole is too large or the one-way valve in the valve is not tightly sealed; the sealing ring on the boom cylinder piston is damaged or Serious wear; the boom cylinder barrel is severely worn or strained; the gap between the flow control valve core and the valve body is too large; the oil temperature is too high.
Troubleshooting:
1) Check the filter, clean or replace it if it is clogged; check and eliminate the cause of excessive oil temperature, and replace it if the oil deteriorates.
2) Check whether the main safety valve is stuck. If it is stuck, just disassemble and clean the main valve core so that it can move freely. If the fault cannot be eliminated, operate the multi-way reversing valve, rotate the adjusting nut of the main safety valve, and observe the system pressure response. If the pressure can be adjusted to the specified value, the fault is basically eliminated.
3) Check whether the hydraulic cylinder piston sealing ring has lost its sealing effect: retract the boom cylinder to the bottom, then remove the high-pressure hose from the outlet joint of the rodless cavity, and continue to operate the boom reversing valve to retract the boom cylinder piston rod further. Since the piston rod has reached its bottom and can no longer move, the pressure continues to increase. Then observe whether there is oil flowing out of the oil outlet. If only a small amount of oil flows out, it means that the sealing ring has not failed. If there is a large oil flow (more than 30mL/min), it means that the sealing ring has failed and should be replaced.
4) Based on the usage time of the multi-way valve, it can be analyzed whether the gap between the valve core and the valve body hole is too large. The normal gap is 0.01mm, and the limit value during repair is 0.04mm. Disassemble and clean the slide valve to eliminate sticking.
5) Check the gap between the flow control valve valve core and the valve body hole. The normal value is 0.015 ~ 0.025mm, and the maximum value does not exceed 0. 04mm. If the gap is too large, the valve should be replaced. Check the sealing of the one-way valve in the valve. If the sealing is poor, grind the valve seat and replace the valve core. Check the spring and replace it if it is deformed, soft or broken.
6) If the above possible causes are eliminated and the fault still exists, the hydraulic pump must be disassembled and inspected. For the CBG gear pump commonly used in this machine, mainly check the end clearance of the pump, and secondly check the meshing clearance between the two gears and the radial clearance between the gear and the shell. If the gap is too large, it means that the leakage is too large and therefore sufficient pressure oil cannot be generated. At this time, the main pump should be replaced. The two end faces of the gear pump are sealed by two steel side plates plated with copper alloy. If the copper alloy on the side plates falls off or is severely worn, the hydraulic pump will not be able to deliver enough pressure oil. The hydraulic pump should also be replaced at this time. Disease stir-fry
7) If the boom lift is weak but the bucket retracts normally, it means that the hydraulic pump, filter, flow distribution valve, main safety valve and oil temperature are normal. Just verify and troubleshoot other aspects.

Due to the limited number of words, this article will introduce two fault analyses. We will see you in the next article. In addition, if your loader needs to purchase relevant loader accessories during maintenance and repair, you can contact us. If you need to buy a new loader or a second-hand loader, you can also contact us. CCMIE provides comprehensive loader sales services.