Excavators often experience delayed front wheel steering during sharp turns while driving. According to KOTAI analysis, based on the working principle of the steering system, it can be determined that this fault is caused by a decrease in the volumetric efficiency of the hydraulic steering system and a low system pressure. Usually, the following methods can be used for inspection and exclusion.
1. Check for leaks on the exterior of the hydraulic steering system
The main symptoms of external oil leakage are: significant loss of hydraulic oil, decreased system pressure, unstable movement of the steering cylinder and motor, resulting in slow and weak steering, and even inability to turn. The main reasons for external leakage are: improper fitting of oil pipe joints, poor sealing, and pipeline rupture; Improper fitting, wear, aging or damage of seals; Excessive oil temperature increases leakage. When external oil leakage is discovered, timely maintenance should be carried out.
2. Check the hydraulic oil
The quality and quantity of hydraulic oil will directly affect the working state of the steering system. When the hydraulic oil is not clean or there are foreign objects in the oil tank, impurities entering the hydraulic system can cause damage to the seals or damage to the components, increasing internal leakage and resulting in slow steering. Therefore, it is necessary to carefully inspect the oil quality of hydraulic oil. If impurities appear in the oil, the hydraulic oil should be replaced in a timely manner and the entire hydraulic system should be cleaned.
3. Check if air has entered the hydraulic steering system
Even a small amount of air entering the hydraulic system can have a significant impact on the system, causing the steering cylinder to crawl and reducing the efficiency of the hydraulic system, resulting in sluggish steering. The ways in which air enters the hydraulic system include: loosening of the joint of the steering pump suction pipe or rupture of the oil pipe; Poor sealing of steering pump; The oil level in the fuel tank is too low, causing the suction pipe or return pipe to protrude from the liquid level; Poor quality of hydraulic oil. The inspection method is to start the engine and observe the oil tank while turning the steering wheel. If there are bubbles in the oil tank, it means that the hydraulic system has entered the air. At this point, it is necessary to identify the cause and eliminate it.
4. Check the steering cylinder
When the piston in the steering cylinder and the seal on the cylinder barrel are worn or damaged, the internal leakage will increase, causing the steering cylinder to move slowly. The inspection method is to remove the steering cylinder and replace it with another excavator with normal steering for testing. If the steering is good after replacement, it indicates that there is no problem with the steering cylinder; If the steering is still slow after replacement, it indicates that the problem lies in the sealing of the steering cylinder. At this time, the steering cylinder should be disassembled and inspected to check the damage of the piston and seals, as well as whether the cylinder barrel has been pulled, and then repaired.
5. Check the steering pump
If there is severe leakage in the steering pump, it can also cause the machine to turn slowly. One important reason for the leakage inside the steering pump is that the gap between the rotor and blade sides of the pump and the end face of the side plate is too large (the normal gap should be within 0.047mm, and the maximum should not exceed 0.100mm). The inspection method is to replace a new pump for comparative testing when the steering cylinder, central rotary joint, and steering gear are all in good condition; If the steering performance is good after replacement, it proves that the fault lies in the steering pump and a new pump should be replaced.
6. Check the central rotary joint
When the inner cylindrical surface or sealing ring at the central rotary joint of the excavator is severely worn, it will cause the entire oil and gas system passing through the rotary joint to interconnect at the sealing failure point, resulting in insensitive movements of all systems in the rotary joint. When the machine is turning, high-pressure oil leaks into the air circuit or other hydraulic pipelines (suspension, support legs, etc.), reducing the amount of hydraulic oil supplied to the steering cylinder and causing the steering cylinder to move slowly. The inspection method is to turn the manual air switch of the wheel brake upwards. If the gas sprayed from inside contains oil mist, it indicates that the central rotary joint has leaked oil into the air circuit due to severe wear. At this point, it is necessary to replace the sealing ring of the central rotary joint and repair the central rotary joint.
7. Check the steering gear motor
When the working surfaces of the stator and rotor of the steering motor or the working surface of the rotary valve are severely worn, it will reduce the actual amount of high-pressure oil entering the steering cylinder, resulting in slow steering action. If the performance of the steering cylinder and central rotary joint is intact, the steering wheel can be killed after the engine is turned off. If the front wheels of the machine can immediately deflect and the hand feel is not heavy, it indicates that there is a problem with the steering gear, which should be repaired or replaced immediately.
8. Check the single channel steady flow valve
When the hydraulic pressure of the hydraulic steering system is too low due to the weakening of the spring force of the one-way steady flow valve, it will cause the steering cylinder to work weakly, resulting in sluggish steering. To address this, the nylon plug on the remote control port of the single channel steady flow valve base can be removed and a pressure gauge can be installed; Then start the engine, turn the steering wheel to the left or right, and place obstacles on the side of the front wheels; At this point, observe the reading on the pressure gauge. If the pressure does not reach 7Mpa, the adjustment screw of the single channel steady flow valve should be properly inserted (the fixing nut needs to be loosened first), and the fault can be eliminated.
