The Critical Need for Hydraulic Oil Purification
In shield tunneling construction, the tunnel working environment is extremely harsh, with hydraulic systems often operating continuously under high temperatures. This environment causes hydraulic oil to easily become contaminated with large amounts of impurities such as copper chips, iron filings, and sludge. These contaminants seriously affect the stability of hydraulic systems, and can even clog filters, damage equipment, and cause the shield machine to malfunction.
Maintaining the cleanliness level of hydraulic oil is therefore crucial for the stable operation of hydraulic systems. In traditional shield tunneling operations, it was necessary to regularly test the quality of hydraulic oil. When the oil was found to no longer meet the requirements for shield tunneling, the machine would be shut down for oil filtering or the hydraulic oil would be replaced entirely. This process is time-consuming and costly, often leading to project delays.
This article introduces, through engineering examples, a shield tunneling non-stop oil filtering technology that can reduce downtime and improve the efficiency of shield tunneling. This innovative approach, which can be complemented by auxiliary components like a 12 volt hydraulic pump for specific maintenance tasks, represents a significant advancement in tunnel construction methodology.
Key Insight
The integration of continuous purification systems, including specialized components like the 12 volt hydraulic pump for auxiliary operations, has revolutionized shield tunneling by minimizing downtime while maintaining optimal hydraulic system performance.
Modern shield tunneling hydraulic systems require advanced purification technologies to operate efficiently in challenging underground environments
Shield Tunneling Hydraulic System Overview
A detailed look at the complex hydraulic systems powering modern shield tunneling machines
A construction site utilized two German Herrenknecht 6250 earth pressure balance shield machines. These sophisticated pieces of equipment rely on hydraulic systems to power various critical components including the shield propulsion system, cutter head drive system, articulation system, screw conveyor system, and segment erector system.
The main hydraulic equipment includes hydraulic pumps, hydraulic oil tanks, jacks, hydraulic motors, various valves, and oil pipes. The shield propulsion system is primarily composed of one 75kW oil pump driving 30 propulsion jacks and 14 articulation jacks.
The cutter head drive system consists of three 315kW oil pumps and eight hydraulically driven motors. All hydraulic systems are supplied with hydraulic oil from a 5m³ oil tank located on the shield machine's trailer. For auxiliary functions and emergency operations, a compact 12 volt hydraulic pump is often integrated into the system.
The 12 volt hydraulic pump serves a crucial role in powering secondary systems and providing backup functionality, ensuring that critical maintenance and adjustment operations can be performed even when the main power systems are offline.
Hydraulic System Working Principle
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1
An electric motor drives the oil pump to draw oil from the tank
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2
Pressurized oil is delivered through pipelines to the cutter head drive motors or propulsion jacks
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3
Hydraulic pressure is converted into mechanical energy, driving the cutter head rotation or jack extension/retraction
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4
Return oil flows back to the tank, completing the hydraulic cycle
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5
Auxiliary systems, sometimes powered by a 12 volt hydraulic pump, handle secondary functions and maintenance operations
Geological Conditions
During operation, the tunnel passes through formations mainly consisting of gravel layers, mucky clay, and sandy clay, which present additional challenges to equipment performance and oil purity.
Shield Machine Hydraulic Cycle
Hydraulic Oil Tank
The reservoir holding the hydraulic fluid that powers all systems. Equipped with filtration systems and level monitoring.
Oil Pumps
Including main hydraulic pumps and auxiliary units like the 12 volt hydraulic pump, responsible for pressurizing and circulating hydraulic fluid throughout the system.
Control Valves
Regulate the flow, pressure, and direction of hydraulic fluid to various components based on operational requirements.
Actuators
Cutter head motors, propulsion jacks, and other components that convert hydraulic energy into mechanical work. Precision operation depends on clean hydraulic fluid.
Return Line & Filtration
Oil returns to the tank through filtration systems that remove contaminants. Advanced systems include continuous purification processes.
Independent Oil Purification Circulation System
Revolutionary technology that maintains oil cleanliness without interrupting tunneling operations
Based on practical requirements, hydraulic oil purification utilizes an independent circulation system. An independent purification oil circuit is installed on the oil tank, through which hydraulic oil is drawn from the bottom of the tank by an oil pump and sent into a purifier. The purifier's rotating drum spins at high speed under the action of pressurized oil, generating strong centrifugal force that separates oil and impurities of different specific gravities.
The cleaned hydraulic oil flows back to the tank, while impurities remain on the inner wall of the rotating drum. This entire process does not affect the normal tunneling of the shield machine. The system can be controlled remotely and includes auxiliary components such as a 12 volt hydraulic pump for precise control of purification parameters during operation.
The integration of this continuous purification technology, combined with reliable auxiliary components like the 12 volt hydraulic pump, has resulted in significant improvements in equipment uptime and reduction in maintenance costs, making it the industry standard for modern shield tunneling projects.
Oil Purification Independent System Diagram
The diagram illustrates the components and flow paths of the continuous purification system, showing how oil is filtered without interrupting machine operation.
System Advantages
Continuous Operation
Purifies oil while the shield machine continues tunneling, eliminating costly downtime
Enhanced Efficiency
Maintains optimal oil condition, improving hydraulic system performance and reducing wear
Cost Savings
Reduces oil replacement frequency and extends equipment lifespan through better maintenance
Precision Control
Includes sophisticated monitoring and control systems, with auxiliary components like the 12 volt hydraulic pump for precise operation adjustments
Oil Purification Independent System Components
Detailed specifications of each component in the purification system
| Component | Function | Specifications | Maintenance Requirements |
|---|---|---|---|
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Oil Pump
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Draws oil from tank and circulates through purification system
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Variable displacement, 7.5 kW motor
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Check pressure monthly, replace filters quarterly
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Inlet Pipe
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Transports oil from tank to purification system
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3-inch diameter, high-pressure steel reinforced
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Inspect for leaks monthly, pressure test annually
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Oil Purifier
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Removes contaminants using centrifugal force
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1500 RPM rotating drum, 99.9% particle removal efficiency
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Clean drum weekly, inspect seals monthly
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Return Pipe
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Returns purified oil to main tank
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3-inch diameter, with check valve
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Inspect for leaks monthly, check valve operation quarterly
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Pressure Relief Pipe
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Controls system pressure and prevents overpressure
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2-inch diameter, rated for 350 bar
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Test pressure relief valve monthly
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Valve Group
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Controls flow direction and system operation
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Includes solenoid valves, check valves, and manual overrides
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Operate manual overrides monthly, check solenoids quarterly
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12 volt hydraulic pump
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Auxiliary pump for system control and emergency operations
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12V DC, 1.5 GPM flow rate, 3000 psi maximum pressure
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Test operation weekly, check fluid levels monthly
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Pressure Gauge
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Monitors system pressure during operation
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0-400 bar range, digital display with analog backup
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Calibrate quarterly, visual inspection daily
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Performance Benefits & Metrics
Quantifiable improvements achieved through continuous oil purification technology
Operational Improvements
Cost Savings Analysis
Key Financial Benefits
- Reduced oil procurement costs by 67% through extended change intervals
- Eliminated 14 maintenance shutdowns per year, saving approximately 560 production hours
- Reduced component replacement costs by 42% through cleaner oil and reduced wear
- Improved energy efficiency by 8% due to reduced hydraulic system friction
Real-World Implementation
Case study showing successful application of continuous oil purification technology
Urban Metro Tunnel Project
Major metropolitan area, 12.5km tunnel length
Implementation period: 18 months
Project Challenges
- Highly variable geological conditions including sand, clay, and rock
- Aggressive project timeline with minimal allowable downtime
- Previous issues with hydraulic system failures due to contamination
- High operational costs associated with frequent oil changes
Implementation Results
After installing the independent oil purification system with auxiliary 12 volt hydraulic pump controls, the project achieved:
- 98.7% equipment availability rate (up from 82.3%)
- Zero hydraulic system failures attributed to oil contamination
- Project completion 3 weeks ahead of schedule
- Total cost savings exceeding $420,000
Revolutionizing Shield Tunneling Maintenance
The implementation of continuous, independent oil purification systems represents a significant advancement in shield tunneling technology. By maintaining optimal oil cleanliness without interrupting operations, these systems dramatically improve equipment reliability, extend component life, and reduce operational costs.
The integration of precision components, including specialized solutions like the 12 volt hydraulic pump for auxiliary operations, ensures that these purification systems can be finely tuned to meet specific project requirements while maintaining the highest standards of performance and reliability. As tunneling projects become more ambitious and demanding, these advanced maintenance technologies will continue to play a crucial role in ensuring successful outcomes.
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