Abstract: This article analyzes several common faults in the hydraulic suspension system of tractors, such as sudden inability to lift agricultural tools, hydraulic pump jamming, and continuous bursting of hydraulic pump housings in a short period of time.
Keywords: tractor hydraulic suspension system; Fault phenomenon; Reason for malfunction; Troubleshooting
1. The hanging agricultural tools suddenly couldn't be lifted
The John Deere 600 wheeled tractor suddenly couldn't lift the hanging plow while working in the field. At this point, check that the hydraulic pump is working properly and the hydraulic oil has entered the distributor, but the suspension plow cannot be lifted. During the process of pulling the slide valve handle lever up or down, there is no pressure and it cannot be positioned or reset.
1.1 Analysis of Fault Causes
Based on the above fault phenomena, it is analyzed that the fault may come from the distributor. So the distributor was removed from the car for inspection. When the distributor was disassembled and inspected, it was found that the lower seat of the slide valve spring and its fixing screw plug, slide valve spring, and boost valve had all fallen into the lower cover of the distributor (the detached parts were undoubtedly located after inspection). After counting the parts, it was found that the fixing screw plug and stop valve plate of the slide valve spring lower seat were missing, which may be the key to the fault.
When the stopper gasket is missing from the distributor (which may have been missed during distributor maintenance), the fixing screw plug of the slide valve spring seat is gradually loosened under the long-term indirect action of the spring until the fixing screw plug is loosened. Due to the detachment of slide valve components, they cannot be positioned, resulting in the suspension plow being unable to lift.
1.2 Troubleshooting
In response to the above fault causes, a fixed screw plug stop gasket was made, and all parts of the slide valve were cleaned. Then, the assembly was carried out according to the correct method, and the fixed screw plug stop gasket was locked firmly. Finally, the distributor assembly was reinstalled on the tractor. After conducting field trials on cultivated land, the results showed that the tractor's suspended plow can be raised and lowered smoothly, and can be positioned and automatically reset.
The following are the precautions to be taken when disassembling and assembling the distributor:
(1) If the boost valve pin is disassembled, it should be scrapped and cannot be reused.
(2) The "0" mark on the slide valve shoulder should be aligned with the direction of the return valve during assembly. Place one of the three small holes on the side of the upper two shoulders of the slide valve towards the direction of the return valve.
(3) Due to the varying lengths of the upper and lower seats of the slide valve spring, during assembly, the longer seat is the lower spring seat and the shorter seat is the upper spring seat.
2. Hydraulic pump stuck
A John Deere 600 wheeled tractor experienced the following phenomenon during plowing operations: while pressing the clutch pedal, the hydraulic pump transmission gear engagement lever was pulled to the engagement position (with the engine idling), and when the clutch pedal was released, the engine immediately shut down (a phenomenon that has not occurred before). This has been tested several times. Only by slightly increasing the throttle while releasing the clutch after the hydraulic pump transmission gear is engaged with the power, can the engine not stall. According to the driver's feedback, since the occurrence of the above phenomenon, the lifting speed of the hydraulic suspension plow has also become slower.
2.1 Analysis of Fault Causes
The inspection is as follows: Before disassembling the hydraulic pump, the hydraulic transmission part was first checked, but no suspicious areas were found; Then remove the hydraulic pump from the body, start the engine, and engage the transmission gear of the hydraulic pump while releasing the clutch pedal. As a result, the engine did not stall at idle, indicating that there was no jamming in the transmission part of the hydraulic pump. Obviously, the problem lies with the hydraulic pump itself.
Based on the above situation, a detailed inspection was conducted on the hydraulic pump: when rotating the hydraulic pump shaft, it was found that one position of the hydraulic pump was very heavy; Sometimes it's not possible to complete a full turn, and only after a few turns of the driving gear can it barely complete a full turn. After repeated rotation several times, it was found that gear jamming always occurred in a fixed position. After inspection, it was found that there were small pits and burrs on the tooth surface of one tooth on the driven gear; At the same time, similar defects were observed on the adjacent tooth surfaces of the defective tooth between the driving gear and the driven gear. As for the causes of tooth surface dents and burrs, they may be due to the presence of hard objects between the tooth surfaces.
2.2 Troubleshooting
Thoroughly repair, clean, and test the meshing and rotation of the burrs on the tooth surface until the main and driven gears of the hydraulic pump mesh and can rotate freely without any jamming. Then thoroughly clean and carefully assemble all parts of the hydraulic pump. After installation, the driving gear shaft can still rotate flexibly without any jamming phenomenon. After the entire tractor is reassembled and tested normally, the hydraulic pump transmission part is engaged, and the main clutch is released. The engine no longer stalls at idle speed, and the hydraulic suspension plow rises and falls relatively quickly.
3. Hydraulic pump casing exploded
During field operations, a John Deere 654 wheeled tractor experienced two consecutive explosions of the hydraulic pump housing in a short period of time.
3.1 Analysis of Fault Causes
Based on the above fault phenomena, it is analyzed that the reason why hydraulic pumps explode is generally due to the high working pressure maintained by the hydraulic system.
The reasons for high working pressure in hydraulic systems are:
(1) The safety valve is stuck in the closed position.
(2) Tractor drivers and maintenance workers adjust the pressure of the safety valve without authorization.
The opening pressure of the safety valve is matched with the carrying pressure of the hydraulic pump. The safety valve pressure has been adjusted at the factory and is generally not allowed to be adjusted arbitrarily. Based on the above fault phenomena, the safety valve was first inspected, and it was found that the depth of the safety valve support from the lower plane of the distributor housing (compared to similar models) was significantly smaller than the normal depth (the normal depth of the safety valve for similar models is 23 ± 0.2 mm), indicating that someone had adjusted the safety valve.
After the safety valve was adjusted without authorization, the working pressure maintained by the hydraulic system rose too high. At this time, the hydraulic pressure exceeded the pressure that the hydraulic pump could withstand, and the distributor safety valve could not unload in time, so the hydraulic pump exploded as a result.
3.2 Troubleshooting
If the tractor discovers insufficient pressure in the hydraulic system during operation, it should first check for leaks in the system and should not make unauthorized adjustments to the safety valve. Generally, the adjustment of the safety valve is carried out on a specialized test bench.
The handling methods for the above faults are as follows:
(1) Eliminate the oil leakage in the hydraulic system.
(2) First, remove the safety valve support, clean the distributor housing and safety valve support, and then adjust the external thread of the safety valve support to the normal position (i.e. the depth of the safety valve support from the lower plane of the distributor housing should reach 23 ± 0.2 mm).
After the above-mentioned faults of the tractor were handled in this way and tested, the above-mentioned faults of the tractor were eliminated.
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2025-05-05