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Fault of excavator without rotation: It was found that there was no rotation movement, while other movements were normal.

When the operating handle is placed in the rotary position, the control oil reaches the control valve and pushes the rotary valve rod to feed the high-pressure oil provided by the rear working oil pump into the rotary motor; At the same time, the oil circuit that controls the oil return to the tank is cut off, increasing the pressure of the brake release valve, pushing its valve stem to allow another auxiliary pressure oil to enter the brake piston, opening the swing brake device, and causing the swing motor to act; The rotary motor outputs power through the small gear of the gearbox, which meshes with the rotary gear ring to generate a rotary motion.

Fault cause analysis and inspection:

From the working principle of the rotary mechanism, there are three reasons for the malfunction, namely the main working oil circuit, mechanical transmission, and control oil circuit.

(1) Inspection of the main working oil circuit

If the pressure of the swing main oil circuit is low, it will not be possible to generate swing action. Measure the pressure of the main working oil circuit system. There is an internal hexagonal oil plug at the pressure outlet of the rear working oil pump. Remove it and install a pressure gauge. Operate the rotary handle to accelerate the diesel engine. The measured pressure reaches 23.5MPa, which is the normal working pressure of the system. This indicates that all hydraulic components in the main working oil circuit are normal.

(2) Inspection of mechanical transmission part

The rotary motor outputs power through the small gear of the transmission, which rotates around the rotary gear ring. During this power output process, if the gears that mesh with each other are jammed, there will also be no rotation action.

Generally, abnormal gear engagement can cause abnormal noise. Currently, the driver has not heard any abnormal sound during operation, so mechanical transmission faults can be temporarily ruled out.

(3) Inspection of control oil circuit

Since all other actions of the excavator are normal, it indicates that the auxiliary oil pump that provides control oil pressure is working normally. There are three control oil circuits for the rotary action, namely the oil circuit that controls the rotary valve stem, brake release valve, and the oil circuit that enters the parking brake piston. The specific analysis is as follows.

When operating the rotary handle, there is a strong oil flu when touching the pressure oil pipe of the rotary motor, indicating that the main working pressure oil has reached the rotary motor, the rotary valve stem of the control valve can be opened normally, and the control oil circuit is working normally. Measure the oil pressure to the parking brake piston. Open the pipe joint of the oil circuit to the rotary motor, install the three-way joint and pressure gauge, and the measured pressure reaches 4MPa, indicating that the pressure of the oil circuit is normal.

Measure the oil pressure to the brake release valve. Open the pipe joint of the oil circuit to the rotary motor, install the three-way joint and pressure gauge, and the measured pressure is 0.4-0.6MPa. Obviously, this pressure is too low (normal working pressure should be 4MPa) to open the brake release valve, and the control oil from the other circuit cannot flow into the brake piston, let alone open the rotary brake device. Therefore, there is no action in the rotation. There are two reasons for the low pressure in this oil circuit. One is that the control valve leaks, causing the oil pressure entering the brake release valve to decrease. (Connect the pressure gauge to the pipe joint of the control oil pipe from the control valve to the brake release valve, and the measured oil pressure is only 0.4-0.6MPa, indicating that the judgment of the control valve leaking is correct.); The second reason is that the brake release valve leaks due to wear and tear, which increases the fit gap (after disassembly and inspection, the valve stem and valve hole fit well and there is no jamming phenomenon).

Troubleshooting: An In-Depth Guide to Diagnosing and Resolving Control Valve Malfunctions in Excavators

Excavators are complex pieces of machinery that rely heavily on their hydraulic systems to perform a variety of tasks, from digging and lifting to rotating and moving. One of the critical components in this hydraulic system is the control valve. The control valve regulates the flow and direction of hydraulic fluid, enabling precise control over the excavator’s movements. However, when a malfunction occurs, it can severely impact the performance and efficiency of the machine. This detailed guide delves into the process of troubleshooting a control valve malfunction, including the steps taken to diagnose the issue, the repair process, and the measures to prevent future problems.

Understanding the Role of Control Valves in Excavators

Control valves are essential for directing hydraulic fluid to different parts of the excavator. They are responsible for controlling the flow rate and pressure of the hydraulic fluid, which in turn controls the speed and force of the machine’s movements. The primary functions of control valves in an excavator include:

• Regulating Fluid Flow: Control valves manage the flow of hydraulic fluid to various actuators, such as cylinders and motors, which drive the excavator’s movements.
• Controlling Direction: By adjusting the direction of fluid flow, control valves determine the direction in which the machine’s components move.
• Maintaining Pressure: Control valves help maintain the necessary pressure levels within the hydraulic system to ensure efficient operation.

Given their critical role, any malfunction in the control valve can lead to significant operational issues, such as erratic movements, reduced power, and complete failure of specific functions.

Symptoms of Control Valve Malfunctions

Before diving into the troubleshooting process, it’s essential to recognize the common symptoms of control valve malfunctions. These symptoms can help in early detection and prompt action to prevent further damage to the excavator. Common signs of control valve issues include:

• Erratic Movements: Inconsistent or jerky movements of the excavator’s arm, bucket, or tracks.
• Loss of Power: Reduced force or speed in hydraulic functions, indicating a possible issue with fluid flow or pressure.
• Hydraulic Fluid Leaks: Visible leaks around the control valve area, suggesting seal or component failure.
• Unusual Noises: Hissing, whining, or knocking sounds from the hydraulic system, which could indicate fluid flow disruptions or air ingress.
• Pregrevanje: Excessive heat in the hydraulic system, often caused by restricted fluid flow or pressure imbalances.

Diagnosing the Control Valve Malfunction

The first step in troubleshooting a control valve malfunction is a thorough diagnosis. This involves a systematic approach to identify the root cause of the problem. Here’s a detailed breakdown of the diagnostic process:

1. Visual Inspection

Begin with a visual inspection of the control valve and the surrounding hydraulic components. Look for signs of wear, damage, or leaks. Pay close attention to the following:

• Seals and Gaskets: Check for any visible cracks, tears, or deterioration in seals and gaskets that might cause fluid leaks.
• Connections and Hoses: Inspect the hydraulic hoses and connections for signs of wear, damage, or loose fittings.
• Valve Body: Examine the control valve body for any signs of physical damage, such as cracks or corrosion.

2. Hydraulic Fluid Analysis

The condition of the hydraulic fluid can provide valuable insights into the health of the control valve and the entire hydraulic system. Perform the following checks:

• Nivo tekočine: Ensure that the hydraulic fluid level is within the recommended range. Low fluid levels can cause air to enter the system, leading to erratic movements and reduced performance.
• Kakovost tekočine: Check the color, viscosity, and presence of contaminants in the hydraulic fluid. Dark, cloudy, or contaminated fluid indicates the need for a fluid change and potential issues with the control valve.

3. Pressure Testing

Pressure testing the hydraulic system can help identify issues related to fluid flow and pressure regulation. Use a hydraulic pressure gauge to perform the following tests:

• System Pressure: Measure the overall system pressure to ensure it is within the manufacturer’s specifications. Deviations from the recommended pressure levels can indicate valve malfunctions.
• Pressure Drops: Check for any significant pressure drops across the control valve, which can suggest internal leaks or blockages.

4. Functional Testing

Conduct functional tests to observe the performance of the control valve under different operating conditions. These tests can help pinpoint specific issues:

• Actuator Response: Operate the excavator’s functions, such as lifting the arm, rotating the body, or moving the tracks, and observe the response. Slow, weak, or inconsistent movements can indicate control valve problems.
• Directional Control: Test the directional control by moving the actuators in various directions. Difficulty in changing direction or delayed responses can be signs of valve issues.

Identifying the Root Cause: Leakage in the Control Valve

In this case study, the primary symptom observed was erratic rotational movements of the excavator. Upon conducting the above diagnostic steps, it was determined that the main cause of the malfunction was leakage in the control valve. Here’s a detailed analysis of the findings:

1. Visual Inspection

During the visual inspection, hydraulic fluid leaks were detected around the control valve area. The seals and gaskets appeared worn and deteriorated, indicating a potential source of the leakage.

2. Hydraulic Fluid Analysis

The hydraulic fluid analysis revealed contamination with particles and moisture, which can accelerate wear and damage to the control valve components. The fluid’s color and viscosity suggested that it had not been changed according to the recommended maintenance schedule.

3. Pressure Testing

Pressure testing indicated significant pressure drops across the control valve, confirming internal leaks. The system pressure was also lower than the manufacturer’s specifications, further supporting the diagnosis of valve leakage.

4. Functional Testing

Functional testing showed inconsistent and weak rotational movements, which aligned with the symptoms of control valve leakage. The directional control was also affected, with delays and difficulties in changing directions.

Repairing the Control Valve

Given the complexity and critical role of the control valve, repairing it requires careful attention and expertise. Here’s a step-by-step guide to the repair process:

1. Removing the Control Valve

To access and repair the control valve, it is necessary to remove it from the excavator. This involves the following steps:

• Odklop hidravličnih vodov: Carefully disconnect the hydraulic lines connected to the control valve, ensuring to cap them to prevent fluid spillage and contamination.
• Odklop električnih priključkov: If the control valve has any electrical connections, disconnect them to facilitate removal.
• Removing Mounting Bolts: Remove the bolts or screws securing the control valve to the hydraulic system or frame.

2. Disassembling the Control Valve

Once the control valve is removed, disassemble it to inspect and replace the damaged components. This involves:

• Opening the Valve Housing: Carefully open the control valve housing, taking note of the arrangement and orientation of internal components.
• Inspecting Internal Components: Examine the internal components, such as seals, gaskets, and valve spools, for signs of wear, damage, or contamination.
• Cleaning and Replacing Parts: Clean all components thoroughly and replace any worn or damaged parts with new ones. Ensure that the replacement parts meet the manufacturer’s specifications.

3. Reassembling the Control Valve

After replacing the damaged components, reassemble the control valve with careful attention to detail:

• Reinstalling Internal Components: Reinstall the internal components in the correct order and orientation, ensuring proper alignment and fit.
• Sealing the Valve Housing: Securely close the valve housing, ensuring that all seals and gaskets are correctly positioned to prevent future leaks.

4. Reinstalling the Control Valve

With the control valve repaired and reassembled, reinstall it into the excavator:

• Mounting the Valve: Secure the control valve to the hydraulic system or frame using the mounting bolts or screws.
• Reconnecting Hydraulic Lines: Reconnect the hydraulic lines, ensuring that they are securely fastened and free from leaks.
• Reconnecting Electrical Connections: If applicable, reconnect any electrical connections.

5. Testing the Repaired Control Valve

After reinstalling the control valve, perform comprehensive tests to ensure that the repair was successful:

• Tlačno preskušanje: Conduct pressure tests to verify that the hydraulic system pressure is within the manufacturer’s specifications and that there are no significant pressure drops across the control valve.
• Funkcionalno testiranje: Operate the excavator’s functions to ensure smooth and consistent movements. Check for any signs of leaks or abnormalities.

Preventing Future Control Valve Malfunctions

To prevent future control valve malfunctions and ensure the longevity of the excavator’s hydraulic system, implement the following maintenance practices:

1. Regular Fluid Checks and Changes

Regularly check the hydraulic fluid level and quality, and change it according to the manufacturer’s recommendations. Using clean, high-quality hydraulic fluid helps prevent contamination and reduces wear on the control valve components.

2. Routine Inspection and Replacement of Seals and Gaskets

Inspect seals and gaskets regularly for signs of wear and deterioration. Replace them as needed to prevent leaks and maintain optimal pressure within the hydraulic system.

3. Regular Maintenance Schedule

Implement a regular maintenance schedule that includes checking the condition of the control valve, hydraulic lines, and other components. Timely maintenance helps identify and address potential issues before they lead to significant malfunctions.

4. Operator Training

Ensure that operators are trained in the correct use and maintenance of the excavator’s hydraulic system. Proper operation and handling can reduce the risk of damage and prolong the lifespan of the control valve and other components.

5. Using Genuine Parts

Always use genuine parts and components that meet the manufacturer’s specifications when repairing or replacing parts of the hydraulic system. This ensures compatibility and reliability, reducing the risk of future malfunctions.