Hydraulic System Fault Analysis and Troubleshooting for Bending Machines
Hydraulic system faults can be numerous and varied. Some are caused by the failure of a single hydraulic component, while others are the result of combined factors involving multiple components within the system. Some faults are due to improper selection or contamination of hydraulic oil, while others may be caused by mechanical, electrical, or external factors.
Some of these faults occur gradually over time, but many can be sudden and unexpected. Many users of hydraulic equipment neglect maintenance, only addressing issues after a breakdown occurs. In order to meet construction schedules or pursue economic benefits, they may even allow the equipment to operate with faults, significantly shortening its lifespan.
Troubleshooting hydraulic equipment often takes from less than half a day to several days. Users are concerned, and some may even consider purchasing new equipment. Hydraulic technology is a relatively new field and can be challenging to master.
So, how can maintenance personnel with limited knowledge of hydraulic technology quickly analyze and identify faults without specialized instruments?
Taking the "Multi-function Bending Machine Hydraulic System" as an example, this article discusses troubleshooting methods.
This machine is used for bending metal products with diameters ranging from 4.5 to 12mm. It consists of three parts: the main machine, the hydraulic station, and the electrical control cabinet.
During operation, common faults of this equipment include:
Firstly, a sudden increase in noise and a decrease in working pressure.
Observe whether there are bubbles in the compressor lubricant in the fuel tank. If there are, it is caused by air entering the system. If not, proceed to step 2.
By observing whether the compressor lubricant contains two types of bubbles - one is a layer of large bubbles on the surface (with little to no lubricant inside), and the other is small bubbles mixed in the lubricant.
The first type of air ingress can be caused by leaks in the hydraulic oil pump's inlet hose, damage to the hydraulic seal of the connector, or damage to the shaft seal of the hydraulic oil pump (the latter is more likely).
Solutions: Replace the inlet hose, replace the hydraulic seal of the connector, or replace the shaft seal of the hydraulic oil pump.
The second type of air ingress is caused by clogging of filter 1 or aging of the oil hose.
Solutions: Clean or replace filter 1 or replace the oil hose (make sure to use acid- and alkali-resistant hose). If the compressor lubricant is very dirty, it must be replaced with new oil of the same type and specification.Adjust speed control valves 6 and 5. When the system is loaded to its rated capacity, touch hydraulic pumps 2 and 3. If the temperature rises rapidly and vibration is abnormal, it indicates internal damage to the pumps.
Solution: Replace or repair the pumps.
Secondly, the system is silent and there is no working pressure.
First, observe whether the oil return at the system's oil return port is normal. If it is normal, listen for the sound of compressor lubricant flowing near speed control valves 5 and 6. If there is, identify which valve is causing the issue and eliminate it. If the oil return is abnormal, it indicates pump damage. Repair or replace the pump.
Lastly, the system is silent, and the working pressure is normal when the gear oil temperature is low but decreases when the temperature is high.
This common fault is difficult to diagnose and resolve using basic methods. It can be addressed using a segmented enumeration approach.
Firstly, analyze the hydraulic schematic diagram. The system is divided into three subsystems (each controlled by one hydraulic cylinder):
The subsystem controlled by electro-hydraulic directional valve 7 is supplied by pump 2.
The two subsystems controlled by electro-hydraulic directional valves 12 and 14 are supplied by pump 3.
Next, we will discuss these two parts.
Preparation criteria:
After the system operates at an abnormal temperature, a fault of decreased working pressure occurs. The system uses plate-mounted hydraulic directional valves (if the valves are bolted, this method can still be used for diagnosis).
According to the installation holes and oil inlet/outlet specifications of electro-hydraulic directional valves 4, 7, 12, and 14, process four blanking plates with a thickness of 12mm and install O-rings on the oil inlet/outlet sides.
First, discuss the subsystem controlled by electro-hydraulic directional valve 7.
Turn off the server and securely block electro-hydraulic directional valve 7 with the corresponding blanking plate to prevent oil leakage. Then, start pump 2 and check if the working pressure rises to the rated value.
If not, proceed to step 2.
If it does, it indicates leakage in the electro-hydraulic directional valve or hydraulic cylinder.
First, inspect the hydraulic cylinder. Method: Remove the modified blanking plate of electro-hydraulic directional valve 7, replace it with the valve, and disassemble the oil inlet of the non-rod chamber of hydraulic cylinder 9 (assuming the cylinder has been retracted). Start the hydraulic oil pump and energize 2YA to check for oil leakage from the disassembled hydraulic cylinder connection.
1) If there is leakage, it indicates damage to the hydraulic seal on the piston rod of hydraulic cylinder 9, which needs to be replaced.
2) If there is no leakage, it is undoubtedly caused by internal leakage in electro-hydraulic directional valve 7. Replace it with a new valve of the same model.
Replace speed control valve 6 with a new one of the same model. If the working pressure reaches the rated value, it indicates valve damage and needs to be replaced. Otherwise, it is caused by aging of hydraulic pump 2, which needs to be replaced with a new pump of the same model.
Then, check the two subsystems driven by pump 3.
Turn off the main machine and securely block electro-hydraulic directional valve 12 with the corresponding blanking plate to prevent oil leakage. Start pump 3 and check if the working pressure of the system is at the rated value.
If it is, refer to step 1 in the section on electro-hydraulic directional valve 7 for inspection.
If not, proceed to step 2 in this section.
Turn off the server and securely block electro-hydraulic directional valve 14 with the corresponding blanking plate to prevent oil leakage. At this time, the blanking plate at electro-hydraulic directional valve 12 remains in the system. Start pump 3 and check if the working pressure of the system is at the rated value.
If it is, refer to step 1 in the section on electro-hydraulic directional valve 7 for inspection.
If not, proceed to step 3 in this section.
Turn off the server and securely block electro-hydraulic directional valve 4 with the corresponding blanking plate to prevent oil leakage. Start pump 3 and check if the working pressure of the system is at the rated value.
If it is, it indicates damage to electro-hydraulic directional valve 4 and needs to be replaced.
If not, it is definitely due to aging of hydraulic pump 3, which needs to be replaced.
Note! After identifying the fault, be sure to remove all blanking plates and replace them with the corresponding electro-hydraulic directional valves to restore normal operation.
This method is basically applicable to the specific analysis of all simple and complex hydraulic system anomalies. It requires relatively low levels of hydraulic transmission system knowledge and technical expertise from maintenance personnel and has certain practical value.